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  • 201.
    Ivády, Viktor
    et al.
    Linköping University, Faculty of Science & Engineering. Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Hungarian Academic Science, Hungary.
    Klimov, Paul V.
    University of Chicago, IL 60637 USA.
    Miao, Kevin C.
    University of Chicago, IL 60637 USA.
    Falk, Abram L.
    University of Chicago, IL 60637 USA; IBM TJ Watson Research Centre, NY 10598 USA.
    Christle, David J.
    University of Chicago, IL 60637 USA.
    Szasz, Krisztian
    Hungarian Academic Science, Hungary.
    Abrikosov, Igor
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, Faculty of Science & Engineering. National University of Science and Technology MISIS, Russia.
    Awschalom, David D.
    University of Chicago, IL 60637 USA.
    Gali, Adam
    Hungarian Academic Science, Hungary; Budapest University of Technology and Econ, Hungary.
    High-Fidelity Bidirectional Nuclear Qubit Initialization in SiC2016In: Physical Review Letters, ISSN 0031-9007, E-ISSN 1079-7114, Vol. 117, no 22, article id 220503Article in journal (Refereed)
    Abstract [en]

    Dynamic nuclear polarization (DNP) is an attractive method for initializing nuclear spins that are strongly coupled to optically active electron spins because it functions at room temperature and does not require strong magnetic fields. In this Letter, we theoretically demonstrate that DNP, with near-unity polarization efficiency, can be generally realized in weakly coupled electron spin-nuclear spin systems. Furthermore, we theoretically and experimentally show that the nuclear spin polarization can be reversed by magnetic field variations as small as 0.8 Gauss. This mechanism offers new avenues for DNP-based sensors and radio-frequency free control of nuclear qubits.

  • 202.
    Mosyagin, Igor
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, Faculty of Science & Engineering.
    Hellman, Olle
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, Faculty of Science & Engineering.
    Olovsson, Weine
    Linköping University, Department of Physics, Chemistry and Biology. Linköping University, Faculty of Science & Engineering.
    Simak, Sergey
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, Faculty of Science & Engineering.
    Abrikosov, Igor
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, Faculty of Science & Engineering. NUST MISIS, Russia.
    Highly Efficient Free Energy Calculations of the Fe Equation of State Using Temperature-Dependent Effective Potential Method2016In: Journal of Physical Chemistry A, ISSN 1089-5639, E-ISSN 1520-5215, Vol. 120, no 43, p. 8761-8768Article in journal (Refereed)
    Abstract [en]

    Free energy calculations at finite temperature based on ab initio molecular dynamics (AIMD) simulations have become possible, but they are still highly computationally demanding. Besides, achieving simultaneously high accuracy of the calculated results and efficiency of the computational algorithm is still a challenge. In this work we describe an efficient algorithm to determine accurate free energies of solids in simulations using the recently proposed temperature-dependent effective potential method (TDEP). We provide a detailed analysis of numerical approximations employed in the TDEP algorithm. We show that for a model system considered in this work, hcp Fe, the obtained thermal equation of state at 2000 K is in excellent agreement with the results of standard calculations within the quasiharmonic approximation.

  • 203.
    Shulumba, Nina
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Nanostructured Materials. Linköping University, Faculty of Science & Engineering. University of Saarland, Germany.
    Raza, Zamaan
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, Faculty of Science & Engineering.
    Hellman, Olle
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, Faculty of Science & Engineering. Division of Engineering and Applied Science, California Institute of Technology, Pasadena, California, USA.
    Janzén, Erik
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, Faculty of Science & Engineering.
    Abrikosov, Igor
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, Faculty of Science & Engineering. Materials Modeling and Development Laboratory, NUST “MISIS”, Moscow, Russia; LACOMAS Laboratory, Tomsk State University, Tomsk, Russia.
    Odén, Magnus
    Linköping University, Department of Physics, Chemistry and Biology, Nanostructured Materials. Linköping University, Faculty of Science & Engineering.
    Impact of anharmonic effects on the phase stability, thermal transport, and electronic properties of AlN2016In: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 94, no 10, article id 104305Article in journal (Refereed)
    Abstract [en]

    Wurtzite aluminium nitride is a technologically important wide band gap semiconductor with an unusually high thermal conductivity, used in optical applications and as a heatsink substrate. Many of its properties depend on an accurate description of its lattice dynamics, which have thus far only been captured in the quasiharmonic approximation. In this work, we demonstrate that anharmonicity has a considerable impact on its phase stability and transport properties, since anharmonicity is much stronger in the rocksalt phase. We compute a pressure-temperature phase diagram of AlN, demonstrating that the rocksalt phase is stabilised by increasing temperature, with respect to the wurtzite phase. We demonstrate that including anharmonicity, we can recover the thermal conductivity of the wurtzite phase (320 Wm−1K−1 under ambient conditions), and compute the hitherto unknown thermal conductivity of the rocksalt phase (96 Wm−1K−1). We also show that the electronic band gap decreases with temperature. These findings provide further evidence that anharmonic effects cannot be ignored in high temperature applications.

  • 204.
    Morchutt, Claudius
    et al.
    Max Planck Institute Solid State Research, Germany; Ecole Polytech Federal Lausanne, Switzerland.
    Björk, Jonas
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, Faculty of Science & Engineering.
    Strasser, Carola
    Max Planck Institute Solid State Research, Germany.
    Starke, Ulrich
    Max Planck Institute Solid State Research, Germany.
    Gutzler, Rico
    Max Planck Institute Solid State Research, Germany.
    Kern, Klaus
    Max Planck Institute Solid State Research, Germany; Ecole Polytech Federal Lausanne, Switzerland.
    Interplay of Chemical and Electronic Structure on the Single-Molecule Level in 2D Polymerization2016In: ACS NANO, ISSN 1936-0851, Vol. 10, no 12, p. 11511-11518Article in journal (Refereed)
    Abstract [en]

    Single layers of covalently linked organic materials in the form of two-dimensional (2D) polymers constitute structures complementary to inorganic 2D materials. The electronic properties of 2D polymers may be manipulated through a deliberate choice of the organic precursors. Here we address the changes in electronic CO structure-from precursor molecule to oligomer by scanning tunneling spectroscopy and ultraviolet photoelectron spectroscopy. For this purpose, we introduce the polymerization reaction of 1,3,5-tris(4-carboxyphenyl)benzene via decarboxylation on Cu(111), which is thoroughly characterized by scanning tunneling microscopy, X-ray photoelectron spectroscopy, and density functional theory calculations. We present a comprehensive study of a contamination-free on-surface coupling scheme and study how dehydrogenation, decarboxylation, and polymerization affect the electronic structure on the molecular level.

  • 205.
    Nilsson, Johan O.
    et al.
    KTH Royal Institute Technology, Sweden.
    Yu Vekilova, Olga
    KTH Royal Institute Technology, Sweden.
    Hellman, Olle
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, Faculty of Science & Engineering.
    Klarbring, Johan
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, Faculty of Science & Engineering.
    Simak, Sergey
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, Faculty of Science & Engineering.
    Skorodumova, Natalia V.
    KTH Royal Institute Technology, Sweden; Uppsala University, Sweden.
    Ionic conductivity in Gd-doped CeO2: Ab initio color-diffusion nonequilibrium molecular dynamics study2016In: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 93, no 2, p. 024102-Article in journal (Refereed)
    Abstract [en]

    A first-principles nonequilibrium molecular dynamics (NEMD) study employing the color-diffusion algorithm has been conducted to obtain the bulk ionic conductivity and the diffusion constant of gadolinium-doped cerium oxide (GDC) in the 850-1150 K temperature range. Being a slow process, ionic diffusion in solids usually requires simulation times that are prohibitively long for ab initio equilibrium molecular dynamics. The use of the color-diffusion algorithm allowed us to substantially speed up the oxygen-ion diffusion. The key parameters of the method, such as field direction and strength as well as color-charge distribution, have been investigated and their optimized values for the considered system have been determined. The calculated ionic conductivity and diffusion constants are in good agreement with available experimental data.

  • 206.
    Klarbring, Johan
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, Faculty of Science & Engineering.
    Vekilova, Olga Yu.
    KTH Royal Institute Technology, Sweden; Uppsala University, Sweden.
    Nilsson, Johan O.
    KTH Royal Institute Technology, Sweden.
    Skorodumova, Natalia V.
    KTH Royal Institute Technology, Sweden; Uppsala University, Sweden.
    Simak, Sergey
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, Faculty of Science & Engineering.
    Ionic conductivity in Sm-doped ceria from first-principles non-equilibrium molecular dynamics2016In: Solid State Ionics, ISSN 0167-2738, E-ISSN 1872-7689, Vol. 296, p. 47-53Article in journal (Refereed)
    Abstract [en]

    Sm-doped ceria is a prospective electrolyte material for intermediate-temperature solid-oxide fuel cells (IT-SOFC). Equilibrium ab initio molecular dynamics (AIMD) studies of oxygen ion diffusion in this material are currently impractical due to the rareness of diffusive events on the accessible timescale. To overcome this issue we have performed ab initio non-equilibrium molecular dynamics calculations of Sm-doped ceria using the color diffusion algorithm. Applying an external force field we have been able to increase the frequency of diffusive events over the simulation time, while keeping the physical mechanism of diffusion intact. We have investigated the temperature dependence of the maximum strength of the applied external field that could be used while maintaining the response of the system in a linear regime. This allows one to obtain the diffusivity at zero field. The bulk ionic conductivity has been calculated and found to match the experimental data well. We have also compared the description of the diffusion process by our method to previous findings and show that the migration mechanism and site preference of oxygen vacancies with respect to the Sm dopants is well reproduced. (C) 2016 Elsevier B.V. All rights reserved.

  • 207.
    Delange, Pascal
    et al.
    University of Paris Saclay, France.
    Ayral, Thomas
    CEA, France.
    Simak, Sergey
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, Faculty of Science & Engineering.
    Ferrero, Michel
    University of Paris Saclay, France; Coll France, France.
    Parcollet, Olivier
    CEA, France.
    Biermann, Silke
    University of Paris Saclay, France; Coll France, France.
    Pourovskii, Leonid
    University of Paris Saclay, France; Coll France, France; National University of Science and Technology MISIS, Russia.
    Large effects of subtle electronic correlations on the energetics of vacancies in alpha-Fe2016In: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 94, no 10, p. 100102-Article in journal (Refereed)
    Abstract [en]

    We study the effect of electronic Coulomb correlations on the vacancy formation energy in paramagnetic alpha-Fe within ab initio dynamical mean-field theory. The calculated value for the formation energy is substantially lower than in standard density-functional calculations and in excellent agreement with experiment. The reduction is caused by an enhancement of electronic correlations at the nearest neighbors of the vacancy. This effect is explained by subtle changes in the corresponding spectral function of the d electrons. The local lattice relaxations around the vacancy are substantially increased by many-body effects.

  • 208.
    Edström, Daniel
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, Faculty of Science & Engineering.
    Sangiovanni, Davide
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, Faculty of Science & Engineering.
    Hultman, Lars
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, Faculty of Science & Engineering.
    Petrov, Ivan
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, Faculty of Science & Engineering. University of Illinois, IL 61801 USA; University of Illinois, IL 61801 USA.
    Greene, Joseph E
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, Faculty of Science & Engineering. University of Illinois, USA.
    Chirita, Valeriu
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, Faculty of Science & Engineering.
    Large-scale molecular dynamics simulations of TiN/TiN(001) epitaxial film growth2016In: Journal of Vacuum Science & Technology. A. Vacuum, Surfaces, and Films, ISSN 0734-2101, E-ISSN 1520-8559, Vol. 34, no 4, p. 041509-1-041509-9Article in journal (Refereed)
    Abstract [en]

    Large-scale classical molecular dynamics simulations of epitaxial TiN/TiN(001) thin film growth at 1200K are carried out using incident flux ratios N/Ti -1, 2, and 4. The films are analyzed as a function of composition, island size distribution, island edge orientation, and vacancy formation. Results show that N/Ti-1 films are globally understoichiometric with dispersed Ti-rich surface regions which serve as traps to nucleate 111-oriented islands, leading to local epitaxial breakdown. Films grown with N/Ti=2 are approximately stoichiometric and the growth mode is closer to layer-by-layer, while N/Ti-4 films are stoichiometric with N-rich surfaces. As N/Ti is increased from 1 to 4, island edges are increasingly polar, i. e., 110-oriented, and N-terminated to accommodate the excess N flux, some of which is lost by reflection of incident N atoms. N vacancies are produced in the surface layer during film deposition with N/Ti-1 due to the formation and subsequent desorption of N-2 molecules composed of a N adatom and a N surface atom, as well as itinerant Ti adatoms pulling up N surface atoms. The N vacancy concentration is significantly reduced as N/Ti is increased to 2; with N/Ti-4, Ti vacancies dominate. Overall, our results show that an insufficient N/Ti ratio leads to surface roughening via nucleation of small dispersed 111 islands, whereas high N/Ti ratios result in surface roughening due to more rapid upper-layer nucleation and mound formation. The growth mode of N/Ti-2 films, which have smoother surfaces, is closer to layer-by-layer. (C) 2016 American Vacuum Society.

  • 209.
    Shulumba, Nina
    et al.
    Linköping University, Department of Physics, Chemistry and Biology. Linköping University, Faculty of Science & Engineering. University of Saarland, Germany.
    Hellman, Olle
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, Faculty of Science & Engineering. CALTECH, CA 91125 USA.
    Raza, Zamaan
    Linköping University, Department of Physics, Chemistry and Biology. Linköping University, Faculty of Science & Engineering.
    Alling, Björn
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, Faculty of Science & Engineering. Max Planck Institute Eisenforsch GmbH, Germany.
    Barrirero, Jenifer
    Linköping University, Department of Physics, Chemistry and Biology. Linköping University, Faculty of Science & Engineering. University of Saarland, Germany.
    Muecklich, Frank
    University of Saarland, Germany.
    Abrikosov, Igor
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, Faculty of Science & Engineering. NUST MISIS, Russia.
    Odén, Magnus
    Linköping University, Department of Physics, Chemistry and Biology, Nanostructured Materials. Linköping University, Faculty of Science & Engineering.
    Lattice Vibrations Change the Solid Solubility of an Alloy at High Temperatures2016In: Physical Review Letters, ISSN 0031-9007, E-ISSN 1079-7114, Vol. 117, no 20, article id 205502Article in journal (Refereed)
    Abstract [en]

    We develop a method to accurately and efficiently determine the vibrational free energy as a function of temperature and volume for substitutional alloys from first principles. Taking Ti1-xAlxN alloy as a model system, we calculate the isostructural phase diagram by finding the global minimum of the free energy corresponding to the true equilibrium state of the system. We demonstrate that the vibrational contribution including anharmonicity and temperature dependence of the mixing enthalpy have a decisive impact on the calculated phase diagram of a Ti1-xAlxN alloy, lowering the maximum temperature for the miscibility gap from 6560 to 2860 K. Our local chemical composition measurements on thermally aged Ti0.5Al0.5N alloys agree with the calculated phase diagram.

  • 210.
    Beličev, P.P.
    et al.
    University of Belgrade, Serbia.
    Gligorić, G.
    University of Belgrade, Serbia.
    Radosavljević, A.
    University of Belgrade, Serbia.
    Maluckov, A.
    University of Belgrade, Serbia.
    Stepić, M.
    University of Belgrade, Serbia.
    Johansson, Magnus
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, Faculty of Science & Engineering.
    Light Localization in Nonlinear Binary Two-Dimensional Lieb Lattices2016In: Abstract Book of RIAO-OPTILAS 2016 / [ed] Moraga, P. and Saavedra, C, Concepción - Chile: CEFOP-UdeC , 2016, p. 80-80Conference paper (Refereed)
    Abstract [en]

    Light localization in photonic lattices (PLs) is a well-known phenomenon which has been investigated during decades. It has been shown that light localization in the linear regime can be achieved by designing PLs with specific geometries, instead of embedding defects or disorder in otherwise periodic lattices [1]. These geometries provide conditions necessary for destructive wave interference, leading to formation of a perfectly flat (dispersionless) energy band. Eigenvectors associated to the flat-band (FB) eigenfrequencies are entirely degenerate and compact states (FB modes) and any superposition of them is nondiffracting. One of the simplest FB lattice patterns is the two-dimensional (2D) Lieb lattice [2,3] in which the primitive cell contains three sites. By appropriate spatial repetition of this fundamental block, it is possible to achieve a FB in the energy spectrum. Light confinement in PLs can also be a consequence of the interplay between nonlinearity and diffraction when these effects cancel each other, leading to formation of solitons. Recently, it has been reported that nonlinearity and “binarism” in quasi-one-dimensional FB systems can increase the range of existence and stability of FB ring modes [4].

    We model a 2D binary Lieb lattice with nonlinearity of Kerr type and analyse numerically and analytically the existence, stability and dynamical properties of various localized modes found to emerge in spectrum. From the derived dispersion relation we found that binarism does not affect the FB. However, due to the presence of additional periodicity, new gaps occur in the energy spectrum above and below the FB and their widths depend on the ratio between coupling constants. Like in the uniform Lieb lattice, we found eigenmodes in the form of a staggered four-peak “ring” structure, but only under certain conditions which require a particular relation between the field amplitudes in neighbouring sites. In the nonlinear regime, ring modes survive in the uniform Lieb lattice but lose their stability moving away from the FB. On the other hand, nonlinearity destroys the existence of ring solutions in the binary Lieb lattice, leading to a new class of stable localized solutions which can be found in minigaps. As in previous kagome and ladder binary nonlinear strips [4], it is shown that the binarism increases the existence range of stable nonlinear localized solutions.

    References

    [1] R. A. Vicencio, M. Johansson, Physical Review A 87, 061803(R) (2013).

    [2] R. A. Vicencio et al., Physical Review Letters 114, 245503 (2015).

    [3] D. Leykam, O. Bahat-Treidel, A. S. Desyatnikov, Physical Review A 86, 031805(R) (2012).

    [4] P. P. Beličev et al., Physical Review E 92, 052916 (2015).

  • 211.
    Faber, Felix A.
    et al.
    Department of Chemistry, University of Basel, Switzerland.
    Lindmaa, Alexander
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, Faculty of Science & Engineering.
    von Lilienfeld, O. Anatole
    Department of Chemistry, University of Basel, Switzerland.
    Armiento, Rickard
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, Faculty of Science & Engineering.
    Machine Learning Energies of 2 Million Elpasolite (AB2D6) Crystals2016In: Physical Review Letters, ISSN 0031-9007, E-ISSN 1079-7114, ISSN 031-9007, Vol. 117, no 13, article id 135502Article in journal (Refereed)
    Abstract [en]

    Elpasolite is the predominant quaternary crystal structure (AlNaK2F6 prototype) reported in the Inorganic Crystal Structure Database. We develop a machine learning model to calculate density functional theory quality formation energies of all ∼2×106 pristine ABC2D6 elpasolite crystals that can be made up from main-group elements (up to bismuth). Our model’s accuracy can be improved systematically, reaching a mean absolute error of 0.1  eV/atom for a training set consisting of 10×103 crystals. Important bonding trends are revealed: fluoride is best suited to fit the coordination of the D site, which lowers the formation energy whereas the opposite is found for carbon. The bonding contribution of the elements A and B is very small on average. Low formation energies result from A and B being late elements from group II, C being a late (group I) element, and D being fluoride. Out of 2×106 crystals, 90 unique structures are predicted to be on the convex hull—among which is NFAl2Ca6, with a peculiar stoichiometry and a negative atomic oxidation state for Al.

  • 212.
    Leonov, I.
    et al.
    University of Augsburg, Germany; National University of Science and Technology MISIS, Russia.
    Pourovskii, L.
    National University of Science and Technology MISIS, Russia; University of Paris Saclay, France; Coll France, France.
    Georges, A.
    University of Paris Saclay, France; Coll France, France; University of Geneva, Switzerland.
    Abrikosov, Igor
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, Faculty of Science & Engineering. National University of Science and Technology MISIS, Russia.
    Magnetic collapse and the behavior of transition metal oxides at high pressure2016In: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 94, no 15, p. 155135-Article in journal (Refereed)
    Abstract [en]

    We report a detail theoretical study of the electronic structure and phase stability of transition metal oxides MnO, FeO, CoO, and NiO in their paramagnetic cubic B1 structure by employing dynamical mean-field theory of correlated electrons combined with ab initio band-structure methods. Our calculations reveal that under pressure these materials exhibit a Mott insulator-metal transition (IMT) which is accompanied by a simultaneous collapse of local magnetic moments and lattice volume, implying a complex interplay between chemical bonding and electronic correlations. Moreover, our results for the transition pressure show a monotonous decrease from similar to 145 to 40 GPa, upon moving from MnO to CoO. In contrast to that, in NiO, magnetic collapse is found to occur at a remarkably higher pressure of similar to 429 GPa. We provide a unified picture of such a behavior and suggest that it is primarily a localized to itinerant moment behavior transition at the IMT that gives rise to magnetic collapse in transition metal oxides.

  • 213.
    Potapkin, V.
    et al.
    Forschungszentrum Julich, Germany.
    Dubrovinsky, L.
    University of Bayreuth, Germany.
    Sergueev, I.
    DESY, Germany.
    Ekholm, Marcus
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, Faculty of Science & Engineering.
    Kantor, I.
    European Synchrotron Radiat Facil, France.
    Bessas, D.
    European Synchrotron Radiat Facil, France.
    Bykova, E.
    University of Bayreuth, Germany.
    Prakapenka, V.
    University of Chicago, IL 60437 USA.
    Hermann, R. P.
    Forschungszentrum Julich, Germany; Oak Ridge National Lab, TN 37831 USA.
    Rueffer, R.
    European Synchrotron Radiat Facil, France.
    Cerantola, V.
    University of Bayreuth, Germany.
    Jönsson, Johan
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, Faculty of Science & Engineering.
    Olovsson, W.
    Linköping University, Department of Physics, Chemistry and Biology. Linköping University, Faculty of Science & Engineering.
    Mankovsky, S.
    University of Munich, Germany.
    Ebert, H.
    University of Munich, Germany.
    Abrikosov, Igor
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, Faculty of Science & Engineering. National University of Science and Technology MISIS, Russia; Tomsk State University, Russia.
    Magnetic interactions in NiO at ultrahigh pressure2016In: PHYSICAL REVIEW B, ISSN 2469-9950, Vol. 93, no 20, p. 201110-Article in journal (Refereed)
    Abstract [en]

    Magnetic properties of NiO have been studied in the multimegabar pressure range by nuclear forward scattering of synchrotron radiation using the 67.4 keV Mossbauer transition of Ni-61. The observed magnetic hyperfine splitting confirms the antiferromagnetic state of NiO up to 280 GPa, the highest pressure where magnetism has been observed so far, in any material. Remarkably, the hyperfine field increases from 8.47 T at ambient pressure to similar to 24 T at the highest pressure, ruling out the possibility of a magnetic collapse. A joint x-ray diffraction and extended x-ray-absorption fine structure investigation reveals that NiO remains in a distorted sodium chloride structure in the entire studied pressure range. Ab initio calculations support the experimental observations, and further indicate a complete absence of Mott transition in NiO up to at least 280 GPa.

  • 214.
    Dahlqvist, Martin
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, Faculty of Science & Engineering.
    Ingason, Arni Sigurdur
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, Faculty of Science & Engineering.
    Alling, Björn
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, Faculty of Science & Engineering.
    Magnus, F.
    Uppsala University, Sweden.
    Thore, Andreas
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, Faculty of Science & Engineering.
    Petruhins, Andrejs
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, Faculty of Science & Engineering.
    Mockuté, Aurelija
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, Faculty of Science & Engineering.
    Arnalds, U. B.
    University of Iceland, Iceland.
    Sahlberg, M.
    Uppsala University, Sweden.
    Hjorvarsson, B.
    Uppsala University, Sweden.
    Abrikosov, Igor
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, Faculty of Science & Engineering. National University of Science and Technology MISIS, Russia; Tomsk State University, Russia.
    Rosén, Johanna
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, Faculty of Science & Engineering.
    Magnetically driven anisotropic structural changes in the atomic laminate Mn2GaC2016In: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 93, no 1, p. 014410-Article in journal (Refereed)
    Abstract [en]

    Inherently layered magnetic materials, such as magnetic M(n+1)AX(n) (MAX) phases, offer an intriguing perspective for use in spintronics applications and as ideal model systems for fundamental studies of complex magnetic phenomena. The MAX phase composition M(n+1)AX(n) consists of M(n+1)AX(n) blocks separated by atomically thin A-layers where M is a transition metal, A an A-group element, X refers to carbon and/or nitrogen, and n is typically 1, 2, or 3. Here, we show that the recently discovered magnetic Mn2GaC MAX phase displays structural changes linked to the magnetic anisotropy, and a rich magnetic phase diagram which can be manipulated through temperature and magnetic field. Using first-principles calculations and Monte Carlo simulations, an essentially one-dimensional (1D) interlayer plethora of two-dimensioanl (2D) Mn-C-Mn trilayers with robust intralayer ferromagnetic spin coupling was revealed. The complex transitions between them were observed to induce magnetically driven anisotropic structural changes. The magnetic behavior as well as structural changes dependent on the temperature and applied magnetic field are explained by the large number of low energy, i.e., close to degenerate, collinear and noncollinear spin configurations that become accessible to the system with a change in volume. These results indicate that the magnetic state can be directly controlled by an applied pressure or through the introduction of stress and show promise for the use of Mn2GaC MAX phases in future magnetoelectric and magnetocaloric applications.

  • 215.
    Sangiovanni, Davide
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, Faculty of Science & Engineering.
    Tasnadi, Ferenc
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, Faculty of Science & Engineering.
    Hultman, Lars
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, Faculty of Science & Engineering.
    Petrov, Ivan
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, Faculty of Science & Engineering. University of Illinois, USA.
    Greene, Joseph E
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, Faculty of Science & Engineering. University of Illinois, USA.
    Chirita, Valeriu
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, Faculty of Science & Engineering.
    N and Ti adatom dynamics on stoichiometric polar TiN(111) surfaces2016In: Surface Science, ISSN 0039-6028, E-ISSN 1879-2758, Vol. 649, p. 72-79Article in journal (Refereed)
    Abstract [en]

    We use molecular dynamics (MD) based on the modified embedded atom method (MEAM) to determine diffusion coefficients and migration pathways for Ti and N adatoms (Ti-ad and N-ad) on TiN(111). The reliability of the classical model-potential is verified by comparison with density functional theory (DFT) results at 0 K. MD simulations carried out at temperatures between 600 and 1800 K show that both Ti-ad and N-ad favor fcc surface sites and migrate among them by passing through metastable hcp positions. We find that N-ad species are considerably more mobile than Ti-ad on TiN(111); contrary to our previous results on TiN(001). In addition, we show that lattice vibrations at finite temperatures strongly modify the potential energy landscape and result in smaller adatom migration energies, E-a = 1.03 for Ti-ad and 0.61 eV for N-ad, compared to 0 K values E-aOK = 1.55 (Ti-ad) and 0.79 eV (N-ad). We also demonstrate that the inclusion of dipole corrections, neglected in previous DFT calculations, is necessary in order to obtain the correct formation energies for polar surfaces such as TiN(111). (C) 2016 Elsevier B.V. All rights reserved.

  • 216.
    Pilch, Iris
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, Faculty of Science & Engineering.
    Caillault, L.
    University of Paris 11, France.
    Minea, T.
    University of Paris 11, France.
    Helmersson, Ulf
    Linköping University, Department of Physics, Chemistry and Biology, Plasma and Coating Physics. Linköping University, Faculty of Science & Engineering.
    Tal, Alexey
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, Faculty of Science & Engineering. National University of Science and Technology MISIS, Russia.
    Abrikosov, Igor
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, Faculty of Science & Engineering. National University of Science and Technology MISIS, Russia.
    Münger, Peter
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, Faculty of Science & Engineering.
    Brenning, Nils
    Linköping University, Department of Physics, Chemistry and Biology, Plasma and Coating Physics. Linköping University, Faculty of Science & Engineering. KTH Royal Institute Technology, Sweden.
    Nanoparticle growth by collection of ions: orbital motion limited theory and collision-enhanced collection2016In: Journal of Physics D: Applied Physics, ISSN 0022-3727, E-ISSN 1361-6463, Vol. 49, no 39, p. 395208-Article in journal (Refereed)
    Abstract [en]

    The growth of nanoparticles in plasma is modeled for situations where the growth is mainly due to the collection of ions of the growth material. The model is based on the classical orbit motion limited (OML) theory with the addition of a collision-enhanced collection (CEC) of ions. The limits for this type of model are assessed with respect to three processes that are not included: evaporation of the growth material, electron field emission, and thermionic emission of electrons. It is found that both evaporation and thermionic emission can be disregarded below a temperature that depends on the nanoparticle material and on the plasma parameters; for copper in our high-density plasma this limit is about 1200 K. Electron field emission can be disregarded above a critical nanoparticle radius, in our case around 1.4 nm. The model is benchmarked, with good agreement, to the growth of copper nanoparticles from a radius of 5 nm-20 nm in a pulsed power hollow cathode discharge. Ion collection by collisions contributes with approximately 10% of the total current to particle growth, in spite of the fact that the collision mean free path is four orders of magnitude longer than the nanoparticle radius.

  • 217.
    Ohlin, Kjell
    et al.
    Ohlin Labs, Sweden.
    Berggren, Karl-Fredrik
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, Faculty of Science & Engineering.
    Patterns beyond Faraday waves: observation of parametric crossover from Faraday instabilities to the formation of vortex lattices in open dual fluid strata2016In: European journal of physics, ISSN 0143-0807, E-ISSN 1361-6404, Vol. 37, no 4, p. 045803-Article in journal (Refereed)
    Abstract [en]

    Faraday first characterised the behaviour of a fluid in a container subjected to vertical periodic oscillations. His study pertaining to hydrodynamic instability, the Faraday instability, has catalysed a myriad of experimental, theoretical, and numerical studies shedding light on the mechanisms responsible for the transition of a system at rest to a new state of well-ordered vibrational patterns at fixed frequencies. Here we study dual strata in a shallow vessel containing distilled water and high-viscosity lubrication oil on top of it. At elevated driving power, beyond the Faraday instability, the top stratum is found to freeze into a rigid pattern with maxima and minima. At the same time there is a dynamic crossover into a new state in the form of a lattice of recirculating vortices in the lower layer containing the water. Instrumentation and the physics behind are analysed in a phenomenological way together with a basic heuristic modelling of the wave field. The study, which is based on relatively low-budget equipment, stems from related art projects that have evolved over the years. The study is of value within basic research as well as in education, especially as more advanced collective project work in e.g. engineering physics, where it invites further studies of pattern formation, the emergence of vortex lattices and complexity.

  • 218.
    Bosak, A.
    et al.
    European Synchrotron Radiat Facil, France.
    Krisch, M.
    European Synchrotron Radiat Facil, France.
    Chumakov, A.
    European Synchrotron Radiat Facil, France.
    Abrikosov, Igor
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, Faculty of Science & Engineering. National University of Science and Technology MISIS, Russia.
    Dubrovinsky, L.
    University of Bayreuth, Germany.
    Possible artifacts in inferring seismic properties from X-ray data2016In: Physics of the Earth and Planetary Interiors, ISSN 0031-9201, E-ISSN 1872-7395, Vol. 260, p. 14-19Article in journal (Refereed)
    Abstract [en]

    We consider the experimental and computational artifacts relevant for the extraction of aggregate elastic properties of polycrystalline materials with particular emphasis on the derivation of seismic velocities. We use the case of iron as an example, and show that the improper use of definitions and neglecting the crystalline anisotropy can result in unexpectedly large errors up to a few percent. (C) 2016 Elsevier B.V. All rights reserved.

  • 219.
    Rastgoo-Lahrood, Atena
    et al.
    Technical University of Munich, Germany; Deutsch Museum, Germany; Nanosyst Initiat Munich, Germany; Centre Nanosci, Germany.
    Björk, Jonas
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, Faculty of Science & Engineering.
    Lischka, Matthias
    Technical University of Munich, Germany; Deutsch Museum, Germany; Nanosyst Initiat Munich, Germany; Centre Nanosci, Germany.
    Eichhorn, Johanna
    Technical University of Munich, Germany; Deutsch Museum, Germany; Nanosyst Initiat Munich, Germany; Centre Nanosci, Germany.
    Kloft, Stephan
    Technical University of Munich, Germany; Deutsch Museum, Germany; Nanosyst Initiat Munich, Germany; Centre Nanosci, Germany.
    Fritton, Massimo
    Technical University of Munich, Germany; Deutsch Museum, Germany; Nanosyst Initiat Munich, Germany; Centre Nanosci, Germany.
    Strunskus, Thomas
    University of Kiel, Germany.
    Samanta, Debabrata
    University of Siegen, Germany.
    Schmittel, Michael
    University of Siegen, Germany.
    Heckl, Wolfgang M.
    Technical University of Munich, Germany; Deutsch Museum, Germany; Nanosyst Initiat Munich, Germany; Centre Nanosci, Germany.
    Lackinger, Markus
    Technical University of Munich, Germany; Deutsch Museum, Germany; Nanosyst Initiat Munich, Germany; Centre Nanosci, Germany.
    Post-Synthetic Decoupling of On-Surface-Synthesized Covalent Nanostructures from Ag(111)2016In: Angewandte Chemie International Edition, ISSN 1433-7851, E-ISSN 1521-3773, Vol. 55, no 27, p. 7650-7654Article in journal (Refereed)
    Abstract [en]

    The on-surface synthesis of covalent organic nanosheets driven by reactive metal surfaces leads to strongly adsorbed organic nanostructures, which conceals their intrinsic properties. Hence, reducing the electronic coupling between the organic networks and commonly used metal surfaces is an important step towards characterization of the true material. We demonstrate that post-synthetic exposure to iodine vapor leads to the intercalation of an iodine monolayer between covalent polyphenylene networks and Ag(111) surfaces. The experimentally observed changes from surface-bound to detached nanosheets are reproduced by DFT simulations. These findings suggest that the intercalation of iodine provides a material that shows geometric and electronic properties substantially closer to those of the freestanding network.

  • 220.
    Tal, Alexey
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, Faculty of Science & Engineering. National University of Science and Technology MISIS, Russia.
    Katsnelson, Mikhail I.
    Radboud University of Nijmegen, Netherlands; Ural Federal University, Russia.
    Ekholm, Marcus
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, Faculty of Science & Engineering.
    Jönsson, Johan
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, Faculty of Science & Engineering.
    Dubrovinsky, Leonid
    University of Bayreuth, Germany.
    Dubrovinskaia, Natalia
    University of Bayreuth, Germany.
    Abrikosov, Igor
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, Faculty of Science & Engineering. National University of Science and Technology MISIS, Russia.
    Pressure-induced crossing of the core levels in 5d metals2016In: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 93, no 20, p. 205150-Article in journal (Refereed)
    Abstract [en]

    A pressure-induced interaction between core electrons, the core-level crossing (CLC) transition, has been observed in hcp Os at P approximate to 400 GPa [L. Dubrovinsky et al., Nature (London) 525, 226 (2015)]. By carrying out a systematic theoretical study for all metals of the 5d series (Hf, Ta, W, Re, Os, Ir, Pt, Au) we have found that the CLC transition is a general effect for this series of metals. While in Pt it occurs at approximate to 1500 GPa, at a pressure substantially higher than in Os, in Ir it occurs already at 80 GPa. Moreover, we predict that in Re the CLC transition may take place already at ambient pressure. We explain the effect of the CLC and analyze the shift of the transition pressure across the series within the Thomas-Fermi model. In particular, we show that the effect has many common features with the atomic collapse in rare-earth elements.

  • 221.
    Tellander, Felix B. A.
    et al.
    Department of Astronomy and Theoretical Physics, Lund Univer-sity, SE- 223 62 Lund, Sweden.
    Ulander, Johan E. M.
    Department of Mathematical Sciences, Chalmers University of Technology, SE-412 96 Gothenburg, Sweden.
    Irina I., Yakimenko
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics.
    Berggren, Karl-Fredrik
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics.
    Probability Current and a Simulation of Particle Separation2016In: Journal of Young Investigators, Vol. 31, p. 1-6Article in journal (Refereed)
    Abstract [en]

    The structure of scattered wave fields and currents is of interest in a variety of fields within physics such as quantum mechanics and optics. Traditionally two-dimensional structures have been investigated; here we focus on three-dimensional structures. We make a generic study of three dimensional quantum box cavities, and our main objective is to visualize the probability current. Visualizations are achieved for complex linear combinations of wave functions with different excitations and with boundary conditions: Dirichlet, Neumann, and mixed. By using different boundary conditions, the results reported here are relevant to many different wave analogues such as microwave billiards and acoustic cavities. Visualization was mainly done through animated images, but a chaotic state was visualized by 3D printing. Our results suggest that if the state of excitation is the same in the different boundary conditions, the current is the same, except at the boundaries of the box. Application to sort nanoparticles in acoustic cavities is considered.

  • 222.
    Yakimenko, Irina I.
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, Faculty of Science & Engineering.
    Berggren, Karl-Fredrik
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, Faculty of Science & Engineering.
    Probing dopants in wide semiconductorquantum point contacts2016In: Journal of Physics: Condensed Matter, ISSN 0953-8984, E-ISSN 1361-648X, Vol. 28, no 10, p. 1-10, article id 105801Article in journal (Refereed)
    Abstract [en]

    Effects of randomly distributed impurities on conductance, spin polarization and electronlocalization in realistic gated semiconductor quantum point contacts (QPCs) have beensimulated numerically. To this end density functional theory in the local spin-densityapproximation has been used. In the case when the donor layer is embedded far from thetwo-dimensional electron gas (2DEG) the electrostatic confinement potential exhibits theconventional parabolic form, and thus the usual ballistic transport phenomena take place bothin the devices with split gates alone and with an additional metallic gate on the top.In the opposite case, i.e. when the randomly distributed donors are placed not far away fromthe 2DEG layer, there are drastic changes like the localization of electrons in the vicinity ofconfinement potential minima which give rise to fluctuations in conductance and resonances.The conductance as a function of the voltage applied to the top gate for asymmetricallycharged split gates has been calculated. In this case resonances in conductance caused byrandomly distributed donors are shifted and decrease in amplitude while the anomaliescaused by interaction effects remain unmodified. It has been also shown that for a wide QPCthe polarization can appear in the form of stripes. The importance of partial ionization ofthe random donors and the possibility of short range order among the ionized donors areemphasized. The motivation for this work is to critically evaluate the nature of impurities andhow to guide the design of high-mobility devices.

  • 223.
    Karimov, A. R.
    et al.
    Russian Academic Science, Russia; National Research Nucl University of MEPhI, Russia.
    Yu, M. Y.
    Zhejiang University, Peoples R China; Ruhr University of Bochum, Germany.
    Stenflo, Lennart
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, Faculty of Science & Engineering.
    Properties and evolution of anisotropic structures in collisionless plasmas2016In: Journal of Plasma Physics, ISSN 0022-3778, E-ISSN 1469-7807, Vol. 82, article id 905820502Article in journal (Refereed)
    Abstract [en]

    A new class of exact electrostatic solutions of the Vlasov-Maxwell equations based on the Jeanss theorem is proposed for studying the evolution and properties of two-dimensional anisotropic plasmas that are far from thermodynamic equilibrium. In particular, the free expansion of a slab of electron-ion plasma into vacuum is investigated.

  • 224.
    Jason, Peter
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, Faculty of Science & Engineering.
    Johansson, Magnus
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, Faculty of Science & Engineering.
    Quantum signatures of charge flipping vortices in the Bose-Hubbard trimer2016In: PHYSICAL REVIEW E, ISSN 2470-0045, Vol. 94, no 5, article id 052215Article in journal (Refereed)
    Abstract [en]

    In this work we study quantum signatures of charge flipping vortices, found in the classical discrete nonlinear Schrodinger trimer, by use of the Bose-Hubbard model. We are able to identify such signatures in the quantum energy eigenstates, for instance when comparing the site amplitudes of the classical charge flipping vortices with the probability distribution over different particle configurations. It is also discussed how to construct quantum states that correspond to the classical charge flipping vortices and which effects can lead to deviations between the classical and quantum dynamics. We also examine properties of certain coherent states: classical-like quantum states that can be used to derive the classical model. Several quantum signatures are identified when studying the dynamics of these coherent states, for example, when comparing the average number of particles on a site with the classical site amplitude, when comparing the quantum and classical currents and topological charge, and when studying the evolution of the quantum probability amplitudes. The flipping of the quantum currents are found to be an especially robust feature of these states.

  • 225.
    Johansson, Magnus
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, Faculty of Science & Engineering.
    Quantum signatures of charge-flipping vortices in the Bose-Hubbard trimer2016Conference paper (Other academic)
  • 226.
    Jason, Peter
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, Faculty of Science & Engineering.
    Johansson, Magnus
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, Faculty of Science & Engineering.
    Quantum Signatures Of Charge-Flipping Vortices In The Bose-HubbardTrimer2016In: Abstract Book of RIAO-OPTILAS 2016 / [ed] Moraga, P. and Saavedra, C, Concepción - Chile: CEFOP-UdeC , 2016, p. 99-99Conference paper (Refereed)
    Abstract [en]

    In this work we study quantum signatures of charge flipping vortices[1], found in the classical discrete nonlinear Schrödinger trimer[2], by use of the Bose-Hubbard model. We are able to identify such signatures in the quantum energy eigenstates, for instance when comparing the site amplitudes of the classical charge flipping vortices with the probability distribution over different particle configurations. It is also discussed how to construct quantum states that correspond to the classical charge flipping vortices, and which effects that can lead to deviations between the classical and quantum dynamics.

    We also examine properties of certain coherent states: classical-like quantum states that can be used to derive the classical model. Several quantum signatures are identified when studying the dynamics of these coherent states, for example when comparing the average number of particles on a site with the classical site amplitude, when comparing the quantum and classical currents and topological charge, and when studying the evolution of the quantum probability amplitudes. The flipping of the quantum currents are found to be an especially robust feature of these states.

    References

    [1] A.S. Desyatnikov, M.R. Dennis, A. Ferrando, Physical Review A 83, 063822 (2011)

    [2] P. Jason, M. Johansson, Physical Review E 91, 022910 (2015).

  • 227.
    Abrikosov, Igor
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, Faculty of Science & Engineering. National University of Science and Technology MISIS, Russia.
    Ponomareva, A. V.
    National University of Science and Technology MISIS, Russia.
    Steneteg, Peter
    Linköping University, Department of Science and Technology, Media and Information Technology. Linköping University, Faculty of Science & Engineering.
    Barannikova, S. A.
    National University of Science and Technology MISIS, Russia; National Research Tomsk State University, Russia; SB RAS, Russia.
    Alling, Björn
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, Faculty of Science & Engineering.
    Recent progress in simulations of the paramagnetic state of magnetic materials2016In: Current opinion in solid state & materials science, ISSN 1359-0286, E-ISSN 1879-0348, Vol. 20, no 2, p. 85-106Article, review/survey (Refereed)
    Abstract [en]

    We review recent developments in the field of first-principles simulations of magnetic materials above the magnetic order disorder transition temperature, focusing mainly on 3d-transition metals, their alloys and compounds. We review theoretical tools, which allow for a description of a system with local moments, which survive, but become disordered in the paramagnetic state, focusing on their advantages and limitations. We discuss applications of these theories for calculations of thermodynamic and mechanical properties of paramagnetic materials. The presented examples include, among others, simulations of phase stability of Fe, Fe-Cr and Fe-Mn alloys, formation energies of vacancies, substitutional and interstitial impurities, as well as their interactions in Fe, calculations of equations of state and elastic moduli for 3d-transition metal alloys and compounds, like CrN and steels. The examples underline the need for a proper treatment of magnetic disorder in these systems. (C) 2015 Elsevier Ltd. All rights reserved.

  • 228.
    Finzel, Kati
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, Faculty of Science & Engineering.
    Reinvestigation of the ideal atomic shell structure and its application in orbital-free density functional theory2016In: Theoretical Chemistry accounts, ISSN 1432-881X, E-ISSN 1432-2234, Vol. 135, no 4, p. 87-Article in journal (Refereed)
    Abstract [en]

    It is shown how to determine the ideal shell radii solely as a function of the nuclear charge. With the help of those ideal shell radii, an approximation to the Pauli potential for atoms in their groundstate can be constructed. The so-called SSB-ideal potential (shell structure-based) yields self-consistent orbital-free electron densities with proper atomic shell structure from Hohenberg-Kohn variational principle.

  • 229.
    Nilsson, Johan O.
    et al.
    KTH Royal Institute Technology, Sweden.
    Leetmaa, Mikael
    Uppsala University, Sweden.
    Vekilova, Olga Yu.
    KTH Royal Institute Technology, Sweden.
    Simak, Sergey
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, Faculty of Science & Engineering.
    Skorodumova, Natalia V.
    KTH Royal Institute Technology, Sweden; Uppsala University, Sweden.
    Statistical error in simulations of Poisson processes: Example of diffusion in solids2016In: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 94, no 8, article id 085206Article in journal (Refereed)
    Abstract [en]

    Simulations of diffusion in solids often produce poor statistics of diffusion events. We present an analytical expression for the statistical error in ion conductivity obtained in such simulations. The error expression is not restricted to any computational method in particular, but valid in the context of simulation of Poisson processes in general. This analytical error expression is verified numerically for the case of Gd-doped ceria by running a large number of kinetic Monte Carlo calculations.

  • 230.
    Skripnyak, V. A.
    et al.
    National Research Tomsk State University, Russia; SB RAS, Russia.
    Emelyanova, E. S.
    National Research Tomsk State University, Russia.
    Sergeev, M. V.
    National Research Tomsk State University, Russia.
    Skripnyak, Natalia
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, Faculty of Science & Engineering. National Research Tomsk State University, Russia.
    Zinovieva, O. S.
    SB RAS, Russia.
    Strength and Plasticity of Fe-Cr Alloys2016In: ADVANCED MATERIALS WITH HIERARCHICAL STRUCTURE FOR NEW TECHNOLOGIES AND RELIABLE STRUCTURES 2016, AMER INST PHYSICS , 2016, Vol. 1783, article id 020208Conference paper (Refereed)
    Abstract [en]

    High-chromium steels are attractive as promising structural materials for applications in nuclear facilities. Using the multilevel modeling, yield stress values of precipitation-hardened Fe-Cr steels are predicted in the temperature range up to 1115 K and pressures up to 10 GPa. The adiabatic curve obtained demonstrates a good correlation with the experimental data for a Fe-Cr-Ni alloy in the pressure range up to 10 GPa.

  • 231.
    Alling, Björn
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, Faculty of Science & Engineering. Max Planck Institute Eisenforsch GmbH, Germany.
    Koermann, F.
    Max Planck Institute Eisenforsch GmbH, Germany; Delft University of Technology, Netherlands.
    Grabowski, B.
    Max Planck Institute Eisenforsch GmbH, Germany.
    Glensk, A.
    Max Planck Institute Eisenforsch GmbH, Germany.
    Abrikosov, Igor
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, Faculty of Science & Engineering. National University of Science and Technology MISIS, Russia.
    Neugebauer, J.
    Max Planck Institute Eisenforsch GmbH, Germany.
    Strong impact of lattice vibrations on electronic and magnetic properties of paramagnetic Fe revealed by disordered local moments molecular dynamics2016In: PHYSICAL REVIEW B, ISSN 2469-9950, Vol. 93, no 22, article id 224411Article in journal (Refereed)
    Abstract [en]

    We study the impact of lattice vibrations on magnetic and electronic properties of paramagnetic bcc and fcc iron at finite temperature, employing the disordered local moments molecular dynamics (DLM-MD) method. Vibrations strongly affect the distribution of local magnetic moments at finite temperature, which in turn correlates with the local atomic volumes. Without the explicit consideration of atomic vibrations, the mean local magnetic moment and mean field derived magnetic entropy of paramagnetic bcc Fe are larger compared to paramagnetic fcc Fe, which would indicate that the magnetic contribution stabilizes the bcc phase at high temperatures. In the present study we show that this assumption is not valid when the coupling between vibrations and magnetism is taken into account. At the gamma-delta transition temperature (1662 K), the lattice distortions cause very similar magnetic moments of both bcc and fcc structures and hence magnetic entropy contributions. This finding can be traced back to the electronic densities of states, which also become increasingly similar between bcc and fcc Fe with increasing temperature. Given the sensitive interplay of the different physical excitation mechanisms, our results illustrate the need for an explicit consideration of vibrational disorder and its impact on electronic and magnetic properties to understand paramagnetic Fe. Furthermore, they suggest that at the gamma-delta transition temperature electronic and magnetic contributions to the Gibbs free energy are extremely similar in bcc and fcc Fe.

  • 232.
    Tholander, Christopher
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, Faculty of Science & Engineering.
    Andersson, C. B. A.
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, Faculty of Science & Engineering.
    Armiento, Rickard
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, Faculty of Science & Engineering.
    Tasnadi, Ferenc
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, Faculty of Science & Engineering.
    Alling, Björn
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, Faculty of Science & Engineering. Max Planck Institute Eisenforsch GmbH, Germany.
    Strong piezoelectric response in stable TiZnN2, ZrZnN2, and HfZnN2 found by ab initio high-throughput approach2016In: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 120, no 22, article id 225102Article in journal (Refereed)
    Abstract [en]

    The phase diagrams of the Ti-Zn-N, Zr-Zn-N, and Hf-Zn-N systems are determined using large-scale high-throughput density functional calculations. Thermodynamically stable ordered phases of TiZnN2, ZrZnN2, and HfZnN2 have been found to be promising candidates in piezoelectric devices/applications for energy harvesting. The identified stable phase of TiZnN2 is an ordered wurtzite superstructure, and the stable phases of ZrZnN2 and HfZnN2 have a layered structure with alternating tetrahedral ZnN and octahedral (Zr, Hf)N layers. All of the TMZnN2 (TM = Ti, Zn, Hf) structures exhibit electronic bandgaps and large piezoelectric constants, d(33)(TiZnN2) = 14.21; d(24)(ZrZnN2) = -26.15, and d(24)(HfZnN2) = -21.99 pC/N. The strong piezoelectric responses and their thermodynamical stability make materials with these phases promising candidates for piezoelectric applications. Published by AIP Publishing.

  • 233.
    Nuala, M.Caffrey
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, Faculty of Science & Engineering.
    Johansson, Leif I
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, Faculty of Science & Engineering.
    Xia, Chao
    Linköping University, Department of Physics, Chemistry and Biology. Linköping University, Faculty of Science & Engineering.
    Armiento, Rickard
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, Faculty of Science & Engineering.
    Abrikosov, Igor
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, Faculty of Science & Engineering. NUST MISIS, Russia; Tomsk State University, Russia.
    Jacobi, Chariya
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, Faculty of Science & Engineering.
    Structural and electronic properties of Li-intercalated graphene on SiC(0001)2016In: Physical Review B: covering condensed matter and materials physics, ISSN 2469-9950, Vol. 93, no 19, p. 195421-1-195421-9Article in journal (Refereed)
    Abstract [en]

    We investigate the structural and electronic properties of Li-intercalated monolayer graphene on SiC(0001) using combined angle-resolved photoemission spectroscopy and first-principles density functional theory. Li intercalates at room temperature both at the interface between the buffer layer and SiC and between the two carbon layers. The graphene is strongly n-doped due to charge transfer from the Li atoms and two pi bands are visible at the (K) over bar point. After heating the sample to 300 degrees C, these pi bands become sharp and have a distinctly different dispersion to that of Bernal-stacked bilayer graphene. We suggest that the Li atoms intercalate between the two carbon layers with an ordered structure, similar to that of bulk LiC6. An AA stacking of these two layers becomes energetically favourable. The pi bands around the (K) over bar point closely resemble the calculated band structure of a C6LiC6 system, where the intercalated Li atoms impose a superpotential on the graphene electronic structure that opens gaps at the Dirac points of the two pi cones.

  • 234.
    Olovsson, Weine
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, Faculty of Science & Engineering.
    Alling, Björn
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, Faculty of Science & Engineering. Max-Planck-Institut für Eisenforschung GmbH, D-402 37 Düsseldorf, Germany.
    Magnuson, Martin
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, Faculty of Science & Engineering.
    Structure and Bonding in Amorphous Cr1−xCx Nanocomposite Thin Films: X‐ray Absorption Spectra and First-Principles Calculations2016In: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 120, no 23, p. 12890-12899Article in journal (Refereed)
    Abstract [en]

    The local structure and chemical bonding in two-phase amorphous Cr1−xCx nanocomposite thin films are investigated by Cr K-edge (1s) X-ray absorption near-edge structure (XANES) and extended X-ray absorption fine structure (EXAFS) spectroscopies in comparison to theory. By utilizing the computationally efficient stochastic quenching (SQ) technique, we reveal the complexity of different Cr-sites in the transition metal carbides, highlighting the need for large scale averaging to obtain theoretical XANES and EXAFS spectra for comparison with measurements. As shown in this work, it is advantageous to use ab initio theory as an assessment to correctly model and fit experimental spectra and investigate the trends of bond lengths and coordination numbers in complex amorphous materials. With sufficient total carbon content (≥30 at. %), we find that the short-range coordination in the amorphous carbide phase exhibit similarities to that of a Cr7C3 ± y structure, while excessive carbons assemble in the amorphous carbon phase.

  • 235.
    Stenflo, Lennart
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, Faculty of Science & Engineering.
    Brodin, G.
    Umeå University, Sweden.
    Temperature effects on large amplitude electron plasma oscillations2016In: Physics of Plasmas, ISSN 1070-664X, E-ISSN 1089-7674, Vol. 23, no 7, article id 074501Article in journal (Refereed)
    Abstract [en]

    We present a very simple model equation that can describe one-dimensional large amplitude electron plasma oscillations. Published by AIP Publishing.

  • 236.
    Karimov, A. R.
    et al.
    National Research Nucl University of MEPhI, Russia; Russian Academic Science, Russia.
    Shatokhin, V. L.
    National Research Nucl University of MEPhI, Russia.
    Yu, M. Y.
    Institute Fus Theory and Simulat, Peoples R China; Ruhr University, Germany.
    Stenflo, Lennart
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, Faculty of Science & Engineering. Umeå University, Sweden.
    The processes of nonequilibrium exchange in rotating plasma flows2016In: II CONFERENCE ON PLASMA and LASER RESEARCH AND TECHNOLOGIES, IOP PUBLISHING LTD , 2016, Vol. 747, article id UNSP 012077Conference paper (Refereed)
    Abstract [en]

    The mechanisms of energy/momentum exchange in rotating and compressing plasma flows have been discussed. It has been shown that such flows are capable of transforming the energy of different degrees of freedom into the energy of one degree owing to the interaction of the coupled nonlinear radial, axial and azimuthal electron-ion oscillations. These processes may lead to the additional acceleration of the flow in azimuthal or axial direction so they might be instrumental for the creation of space thrusters employing pulse transformations for propulsion.

  • 237.
    Mozafari, Elham
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, Faculty of Science & Engineering.
    Theoretical Description of the Electron-Lattice Interaction in Molecular and Magnetic Crystals2016Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Electron-lattice interactions are often considered not to play a major role in material's properties as they are assumed to be small, the second-order effects. However, this study shows the importance of taking these effects into account in the simulations. My results demonstrate the impact of the electron-lattice interaction on the physics of the material and our understanding from it. One way to study these effects is to add them as perturbations to the unperturbed Hamiltonians in numerical simulations. The main objective of this thesis is to study electron-lattice interactions in molecular and magnetic crystals. It is devoted to developing numerical techniques considering model Hamiltonians and first-principles calculations to include the effect of lattice vibrations in the simulations of the above mentioned classes of materials.

    In particular, I study the effect of adding the non-local electron-phonon coupling on top of the Holstein Hamiltonian to study the polaron stability and polaron dynamics in molecular crystals. The numerical calculations are based on the semi-empirical Holstein-Peierls model in which both intra (Holstein) and inter (Peierls) molecular electron-phonon interactions are taken into account. I study the effect of different parameters including intra and intermolecular electron-phonon coupling strengths and their vibrational frequencies, the transfer integral and the electric field on polaron stability. I found that in an ordered two dimensional molecular lattice the polaron is stable for only a limited range of parameter sets with the polaron formation energies lying in the range between 50 to 100 meV. Using the stable polaron solutions, I applied an electric field to the system and I observed that the polaron is dynamically stable and mobile for only a limited set of parameters. Adding disorder to the system will result in even more restricted parameter set space for which the polaron is stable and moves adiabatically with a constant velocity. In order to study the effect of temperature on polaron dynamics, I include a random force in Newtonian equations of motion in a one dimensional molecular lattice. I found that there is a critical temperature above which the polaron destabilizes and becomes delocalized.

    Moreover, I study the role of lattice vibrations coupled to magnetic degrees of freedom in finite temperature paramagnetic state of magnetic materials. Calculating the properties of paramagnetic materials at elevated temperatures is a cumbersome task. In this thesis, I present a new method which allows us to couple lattice vibrations and magnetic disorder above the magnetic transition temperature and treat them on the same footing. The method is based on the combination of disordered local moments model and ab initio molecular dynamics (DLM-MD). I employ the method to study different physical properties of some model systems such as CrN and NiO in which the interaction between the magnetic and lattice degrees of freedom is very strong making them very good candidates for such a study.

    I calculate the formation energies and study the effect of nitrogen defects on the electronic structure of paramagnetic CrN at high temperatures. Using this method I also study the temperature dependent elastic properties of paramagnetic CrN. The results highlight the importance of taking into account the magnetic excitations and lattice vibrations in the studies of magnetic materials at finite temperatures. A combination of DLM-MD with another numerical technique namely temperature dependent effective potential (TDEP) method is used to study the vibrational free energy and phase stability of CrN. We found that the combination of magnetic and vibrational contributions to the free energy shifts down the phase boundary between the cubic paramagnetic and orthorhombic antiferromagnetic phases of CrN towards the experimental value.

    I used the stress-strain relation to study the temperature-dependent elastic properties of paramagnetic materials within DLM-MD with CrN as my model system. The results from a combinimation of DLM-MD with another newly developed method, symmetry imposed force constants (SIFC) in conjunction with TDEP is also presented as comparison to DLM-MD results.I also apply DLM-MD method to study the electronic structure of NiO in its paramagnetic state at finite temperatures. I found that lattice vibrations have a prominent impact on the electronic structure of paramagnetic NiO at high temperatures and should be included for the proper description of the density of states.

    In summary, I believe that the proposed techniques give reliable results and allow us to include the effects from electron-lattice interaction in simulations of materials.

    List of papers
    1. Polaron stability in molecular crystals
    Open this publication in new window or tab >>Polaron stability in molecular crystals
    2012 (English)In: Physics Letters A, ISSN 0375-9601, E-ISSN 1873-2429, Vol. 376, no 22, p. 1807-1811Article in journal (Refereed) Published
    Abstract [en]

    A semi-empirical Peierls-Holstein model is applied to studies of the stability of polarons in two-dimensional molecular crystal systems. Calculations for a broad range of intra- and inter-molecular parameters within this model were performed in order to obtain detailed knowledge concerning the stability of the polaron solution with respect to a rigid lattice band solution. For realistic values of the parameters the polaron solution is stable with a polaron energy in the range 50-100 meV. A metastable polaron solution is also identified. The polarons that result from our model are highly localized and it is questionable if adiabatic polaron transport can occur in the system.

    Place, publisher, year, edition, pages
    Elsevier, 2012
    National Category
    Engineering and Technology
    Identifiers
    urn:nbn:se:liu:diva-78584 (URN)10.1016/j.physleta.2012.04.007 (DOI)000304338100010 ()
    Note
    Funding Agencies|Swedish Research Council (VR)||Available from: 2012-06-15 Created: 2012-06-15 Last updated: 2017-12-07
    2. Polaron dynamics in a two-dimensional Holstein-Peierls system
    Open this publication in new window or tab >>Polaron dynamics in a two-dimensional Holstein-Peierls system
    2013 (English)In: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 138, no 18, p. 184104-Article in journal (Refereed) Published
    Abstract [en]

    A semiclassical model for studying charge transport in a two-dimensional molecular lattice is presented and applied to both a well ordered system and a system with disorder. The model includes both intra- and inter-molecular electron-lattice interactions and the focus of the studies is to describe the dynamics of a charge carrier in the system. In particular, we study the dynamics of the system in which the polaron solution is dynamically stable. It is found that the parameter space for which the polaron is moving through the system is quite restricted and that the polaron is immobile for large electron-phonon coupling and weak intermolecular electron interactions and dynamically unstable and disassociates into a delocalized electronic state decoupled from the lattice for small electron-phonon coupling and strong intermolecular electron interactions. Disorder further limits the parameter space in which the polaron is mobile.

    National Category
    Engineering and Technology
    Identifiers
    urn:nbn:se:liu:diva-88110 (URN)10.1063/1.4803691 (DOI)000319290800009 ()23676026 (PubMedID)
    Note

    Funding Agencies|Swedish Research Council (VR)||

    Available from: 2013-01-30 Created: 2013-01-30 Last updated: 2017-12-06Bibliographically approved
    3. Role of N defects in paramagnetic CrN at finite temperatures from first principles
    Open this publication in new window or tab >>Role of N defects in paramagnetic CrN at finite temperatures from first principles
    2015 (English)In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 91, no 9, p. 094101-Article in journal (Refereed) Published
    Abstract [en]

    Simulations of defects in paramagnetic materials at high temperature constitute a formidable challenge to solid-state theory due to the interaction of magnetic disorder, vibrations, and structural relaxations. CrN is a material where these effects are particularly large due to a strong magnetolattice coupling and a tendency for deviations from the nominal 1: 1 stoichiometry. In this work, we present a first-principles study of nitrogen vacancies and nitrogen interstitials in CrN at elevated temperature. We report on formation energetics, the geometry of interstitial nitrogen dimers, and the impact on the electronic structure caused by the defects. We find a vacancy formation energy of 2.28 eV with a small effect of temperature, i.e., a formation energy for N interstitial in the form of a less than 111 greater than -oriented split bond of 3.77 eV with an increase to 3.97 at 1000 K. Vacancies are found to add three electrons, while split-bond interstitial adds one electron to the conduction band. The band gap of defect-free CrN is smeared out due to vibrations, although it is difficult to draw a conclusion about the exact temperature at which the band gap closes from our calculations. However, it is clear that at 900 K there is a nonzero density of electronic states at the Fermi level. At 300 K, our results indicate a border case where the band gap is about to close.

    Place, publisher, year, edition, pages
    American Physical Society, 2015
    National Category
    Physical Sciences Electrical Engineering, Electronic Engineering, Information Engineering
    Identifiers
    urn:nbn:se:liu:diva-116954 (URN)10.1103/PhysRevB.91.094101 (DOI)000350994400001 ()
    Note

    Funding Agencies|Swedish Research Council (VR) [621-2011-4426]; Ministry of Education and Science of the Russian Federation [14.Y26.31.0005]; Tomsk State University Academic D. I. Mendeleev Fund Program; VR [621-2011-4417]

    Available from: 2015-04-13 Created: 2015-04-10 Last updated: 2017-12-04
    4. Finite-temperature elastic constants of paramagnetic materials within the disordered local moment picture from ab initio molecular dynamics calculations
    Open this publication in new window or tab >>Finite-temperature elastic constants of paramagnetic materials within the disordered local moment picture from ab initio molecular dynamics calculations
    Show others...
    2016 (English)In: Physical Review B, ISSN 2469-9950, Vol. 94, no 5, article id 054111Article in journal (Refereed) Published
    Abstract [en]

    We present a theoretical scheme to calculate the elastic constants of magnetic materials in the high-temperature paramagnetic state. Our approach is based on a combination of disordered local moments picture and ab initio molecular dynamics (DLM-MD). Moreover, we investigate a possibility to enhance the efficiency of the simulations of elastic properties using the recently introduced method: symmetry imposed force constant temperature-dependent effective potential (SIFC-TDEP). We have chosen cubic paramagnetic CrN as a model system. This is done due to its technological importance and its demonstrated strong coupling between magnetic and lattice degrees of freedom. We have studied the temperature-dependent single-crystal and polycrystalline elastic constants of paramagentic CrN up to 1200 K. The obtained results at T = 300 K agree well with the experimental values of polycrystalline elastic constants as well as the Poisson ratio at room temperature. We observe that the Young’s modulus is strongly dependent on temperature, decreasing by 14% from T = 300 K to 1200 K. In addition we have studied the elastic anisotropy of CrN as a function of temperature and we observe that CrN becomes substantially more isotropic as the temperature increases. We demonstrate that the use of Birch law may lead to substantial errors for calculations of temperature induced changes of elastic moduli. The proposed methodology can be used for accurate predictions of mechanical properties of magnetic materials at temperatures above their magnetic order-disorder phase transition.

    Place, publisher, year, edition, pages
    AMER PHYSICAL SOC, 2016
    National Category
    Physical Sciences Condensed Matter Physics
    Identifiers
    urn:nbn:se:liu:diva-130779 (URN)10.1103/PhysRevB.94.054111 (DOI)000381475300002 ()
    Note

    Funding agencies. Swedish Research Council (VR) [621-2011-4426, 621-2011-4417, 330-2014-6336]; Swedish Foundation for Strategic Research (SSF) program SRL [10-0026]; Ministry of Education and Science of the Russian Federation [K2-2016-013, 14.Y26.31.0005]; Marie Sklodowska

    Available from: 2016-08-23 Created: 2016-08-23 Last updated: 2016-09-26Bibliographically approved
    5. Vibrational free energy and phase stability of paramagnetic and antiferromagnetic CrN from ab initio molecular dynamics
    Open this publication in new window or tab >>Vibrational free energy and phase stability of paramagnetic and antiferromagnetic CrN from ab initio molecular dynamics
    Show others...
    2014 (English)In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 89, no 17, p. 174108-Article in journal (Refereed) Published
    Abstract [en]

    We present a theoretical first-principles method to calculate the free energy of a magnetic system in its high-temperature paramagnetic phase, including vibrational, electronic, and magnetic contributions. The method for calculating free energies is based on ab initio molecular dynamics and combines a treatment of disordered magnetism using disordered local moments molecular dynamics with the temperature-dependent effective potential method to obtain the vibrational contribution to the free energy. We illustrate the applicability of the method by obtaining the anharmonic free energy for the paramagnetic cubic and the antiferromagnetic orthorhombic phases of chromium nitride. The influence of lattice dynamics on the transition between the two phases is demonstrated by constructing the temperature-pressure phase diagram.

    Place, publisher, year, edition, pages
    American Physical Society, 2014
    National Category
    Physical Sciences
    Identifiers
    urn:nbn:se:liu:diva-110985 (URN)10.1103/PhysRevB.89.174108 (DOI)000341308600001 ()
    Note

    Funding Agencies|Erasmus Mundus Joint European Doctoral Programme DocMASE; SECO Tools AB; Swedish Research Council [621-2011-4426, 621-2011-4417]; Swedish Foundation for Strategic Research (SSF) programs SRL [10-0026]; project Designed Multicomponent Coatings (MultiFilms); Knut and Alice Wallenberg Foundation (KAW)

    Available from: 2014-10-01 Created: 2014-10-01 Last updated: 2017-12-05Bibliographically approved
  • 238.
    Jason, Peter
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, Faculty of Science & Engineering.
    Theoretical studies of Bose-Hubbard and discrete nonlinear Schrödinger models: Localization, vortices, and quantum-classical correspondence2016Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    This thesis is mainly concerned with theoretical studies of two types of models:  quantum mechanical Bose-Hubbard models and (semi-)classical discrete nonlinear Schrödinger (DNLS) models.

    Bose-Hubbard models have in the last few decades been widely used to describe Bose-Einstein condensates placed in periodic optical potentials, a hot research topic with promising future applications within quantum computations and quantum simulations. The Bose-Hubbard model, in its simplest form, describes the competition between tunneling of particles between neighboring potential wells (`sites') and their on-site interactions (can be either repulsive or attractive). We will also consider extensions of the basic models, with additional interactions and tunneling processes.

    While Bose-Hubbard models describe the behavior of a collection of particles in a lattice, the DNLS description is in terms of a classical field on each site. DNLS models can also be applicable for Bose-Einstein condensates in periodic potentials, but in the limit of many bosons per site, where quantum fluctuations are negligible and a description in terms of average values is valid. The particle interactions of the Bose-Hubbard models become  nonlinearities in the DNLS models, so that the DNLS model, in its simplest form, describes a competition between on-site nonlinearity and tunneling to neighboring sites. DNLS models are however also applicable for several other physical systems, most notably for nonlinear waveguide arrays, another rapidly evolving research field.

    The research presented in this thesis can be roughly divided into two parts:

    1) We have studied certain families of solutions to the DNLS model.

    First, we have considered charge flipping vortices in DNLS trimers and hexamers. Vortices represent a rotational flow of energy, and a charge flipping vortex is one where the rotational direction (repeatedly) changes. We have found that charge flipping vortices indeed exist in these systems, and that they belong to continuous families of solutions located between two stationary solutions.

    Second, we have studied discrete breathers, which are spatially localized and time-periodic solutions, in a DNLS models with the geometry of a ring coupled to an additional, central site. We found under which parameter values these solutions exist, and also studied the properties of their continuous solution families. We found that these families undergo different bifurcations, and that, for example, the discrete breathers which have a peak on one and two (neighboring) sites, respectively, belong to the same family below a critical value of the ring-to-central-site coupling, but to separate families for values above it.

    2) Since Bose-Hubbard models can be approximated with DNLS models in the limit of a large number of bosons per site, we studied signatures of certain classical solutions and structures of DNLS models in the corresponding Bose-Hubbard models.

    These studies have partly focused on quantum lattice compactons. The corresponding classical lattice compactons are solutions to an extended DNLS model, and consist of a cluster of excited sites, with the rest of the sites exactly zero (generally localized solutions have nonzero `tails'). We find that only one-site classical lattice compactons remain compact for the Bose-Hubbard model, while for several-site classical compactons there are nonzero probabilities to find particles spread out over more sites in the quantum model. We have furthermore studied the dynamics, with emphasize on mobility, of quantum states that correspond to the classical lattice compactons. The main result is that it indeed is possible to see signatures of the  classical compactons' good mobility, but that it is then necessary to give the quantum state a `hard kick' (corresponding to a large phase gradient). Otherwise, the time scales for quantum fluctuations and for the compacton to travel one site become of the same order.

    We have also studied the quantum signatures of a certain type of instability (oscillatory) which a specific solution to the DNLS trimer experiences in a parameter regime. We have been able to identify signatures in the quantum energy spectrum, where in the unstable parameter regime the relevant eigenstates undergo many avoided crossings, giving a strong mixing between the eigenstates. We also introduced several measures, which either drop or increase significantly in the regime of instability.

    Finally, we have studied quantum signatures of the charge flipping vortices mentioned above, and found several such, for example when considering the correlation of currents between different sites.

    List of papers
    1. Exact localized eigenstates for an extended Bose-Hubbard model with pair-correlated hopping
    Open this publication in new window or tab >>Exact localized eigenstates for an extended Bose-Hubbard model with pair-correlated hopping
    2012 (English)In: Physical Review A. Atomic, Molecular, and Optical Physics, ISSN 1050-2947, E-ISSN 1094-1622, Vol. 85, no 1, p. 016603(R)-Article in journal (Refereed) Published
    Abstract [en]

    We show that a Bose-Hubbard model extended with pair-correlated hopping has exact eigenstates, quantum lattice compactons, with complete single-site localization. These appear at parameter values where the one-particle tunneling is exactly canceled by nonlocal pair correlations, and correspond in a classical limit to compact solutions of an extended discrete nonlinear Schrödinger model. Classical compactons at other parameter values, as well as multisite compactons, generically get delocalized by quantum effects, but strong localization appears asymptotically for increasing particle number.

    Place, publisher, year, edition, pages
    American Physical Society, 2012
    National Category
    Atom and Molecular Physics and Optics
    Identifiers
    urn:nbn:se:liu:diva-73926 (URN)10.1103/PhysRevA.85.011603 (DOI)000298861100001 ()
    Note
    Funding agencies|Swedish Research Council||Available from: 2012-01-16 Created: 2012-01-16 Last updated: 2017-12-08
    2. Quantum signatures of an oscillatory instability in the Bose-Hubbard trimer
    Open this publication in new window or tab >>Quantum signatures of an oscillatory instability in the Bose-Hubbard trimer
    2012 (English)In: Physical Review E. Statistical, Nonlinear, and Soft Matter Physics, ISSN 1539-3755, E-ISSN 1550-2376, Vol. 86, no 1, p. 016214-Article in journal (Refereed) Published
    Abstract [en]

    We study the Bose-Hubbard model for three sites in a symmetric, triangular configuration and search for quantum signatures of the classical regime of oscillatory instabilities, known to appear through Hamiltonian Hopf bifurcations for the "single-depleted-well" family of stationary states in the discrete nonlinear Schrodinger equation. In the regimes of classical stability, single quantum eigenstates with properties analogous to those of the classical stationary states can be identified already for rather small particle numbers. On the other hand, in the instability regime the interaction with other eigenstates through avoided crossings leads to strong mixing, and no single eigenstate with classical-like properties can be seen. We compare the quantum dynamics resulting from initial conditions taken as perturbed quantum eigenstates and SU(3) coherent states, respectively, in a quantum-semiclassical transitional regime of 10-100 particles. While the perturbed quantum eigenstates do not show a classical-like behavior in the instability regime, a coherent state behaves analogously to a perturbed classical stationary state, and exhibits initially resonant oscillations with oscillation frequencies well described by classical internal-mode oscillations.

    Place, publisher, year, edition, pages
    American Physical Society, 2012
    National Category
    Engineering and Technology
    Identifiers
    urn:nbn:se:liu:diva-79982 (URN)10.1103/PhysRevE.86.016214 (DOI)000306470900001 ()
    Note

    Funding Agencies|Swedish Research Council||Swedish Institute||

    Available from: 2012-08-17 Created: 2012-08-17 Last updated: 2017-12-07
    3. Quantum dynamics of lattice states with compact support in an extended Bose-Hubbard model
    Open this publication in new window or tab >>Quantum dynamics of lattice states with compact support in an extended Bose-Hubbard model
    2013 (English)In: Physical Review A. Atomic, Molecular, and Optical Physics, ISSN 1050-2947, E-ISSN 1094-1622, Vol. 88, no 3, p. 033605-Article in journal (Refereed) Published
    Abstract [en]

    We study the dynamical properties, with special emphasis on mobility, of quantum lattice compactons (QLCs) in a one-dimensional Bose-Hubbard model extended with pair-correlated hopping. These are quantum counterparts of classical lattice compactons (localized solutions with exact zero amplitude outside a given region) of an extended discrete nonlinear Schrödinger equation, which can be derived in the classical limit from the extended Bose-Hubbard model. While an exact one-site QLC eigenstate corresponds to a classical one-site compacton, the compact support of classical several-site compactons is destroyed by quantum fluctuations. We show that it is possible to reproduce the stability exchange regions of the one-site and two-site localized solutions in the classical model with properly chosen quantum states. Quantum dynamical simulations are performed for two different types of initial conditions: “localized ground states” which are localized wave packets built from superpositions of compactonlike eigenstates, and SU(4) coherent states corresponding to classical two-site compactons. Clear signatures of the mobility of classical lattice compactons are seen, but this crucially depends on the magnitude of the applied phase gradient. For small phase gradients, which classically correspond to a slow coherent motion, the quantum time scale is of the same order as the time scale of the translational motion, and the classical mobility is therefore destroyed by quantum fluctuations. For a large phase instead, corresponding to fast classical motion, the time scales separate so that a mobile, localized, coherent quantum state can be translated many sites for particle numbers already of the order of 10.

    Place, publisher, year, edition, pages
    American Physical Society, 2013
    National Category
    Engineering and Technology
    Identifiers
    urn:nbn:se:liu:diva-98144 (URN)10.1103/PhysRevA.88.033605 (DOI)000323942100007 ()
    Note

    Funding Agencies|Swedish Research Council||

    Available from: 2013-09-30 Created: 2013-09-30 Last updated: 2017-12-06
    4. Charge flipping vortices in the discrete nonlinear Schrodinger trimer and hexamer
    Open this publication in new window or tab >>Charge flipping vortices in the discrete nonlinear Schrodinger trimer and hexamer
    2015 (English)In: Physical Review E. Statistical, Nonlinear, and Soft Matter Physics, ISSN 1539-3755, E-ISSN 1550-2376, Vol. 91, no 2, p. 022910-Article in journal (Refereed) Published
    Abstract [en]

    We examine the existence and properties of charge flipping vortices (CFVs), vortices which periodically flip the topological charge, in three-site (trimer) and six-site (hexamer) discrete nonlinear Schrodinger lattices. We demonstrate numerically that CFVs exist as exact quasiperiodic solutions in continuous families which connect two different stationary solutions without topological charge, and that it is possible to interpret the dynamics of certain CFVs as the result of perturbations of these stationary solutions. The CFVs are calculated with high numerical accuracy and we may therefore accurately determine many of their properties, such as their energy and linear stability, and the CFVs are found to be stable over large parameter regimes. We also show that, like in earlier studies for lattices with a multiple of four sites, trimer and hexamer CFVs can be obtained by perturbing stationary constant amplitude vortices with certain linear eigenmodes. However, in contrast to the former case where the perturbation could be infinitesimal, the magnitude of the perturbations for trimers and hexamers must overcome a quite large threshold value. These CFVs may be interpreted as exact quasiperiodic CFVs, with a small perturbation applied. The concept of a charge flipping energy barrier is introduced and discussed.

    Place, publisher, year, edition, pages
    American Physical Society, 2015
    National Category
    Physical Sciences
    Identifiers
    urn:nbn:se:liu:diva-117256 (URN)10.1103/PhysRevE.91.022910 (DOI)000351205700005 ()
    Note

    Funding Agencies|Swedish Research Council

    Available from: 2015-04-22 Created: 2015-04-21 Last updated: 2017-12-04
    5. Discrete breathers for a discrete nonlinear Schrodinger ring coupled to a central site
    Open this publication in new window or tab >>Discrete breathers for a discrete nonlinear Schrodinger ring coupled to a central site
    2016 (English)In: Physical Review E. Statistical, Nonlinear, and Soft Matter Physics: Statistical Physics, Plasmas, Fluids, and Related Interdisciplinary Topics, ISSN 1063-651X, E-ISSN 1095-3787, Vol. 93, no 1, p. 012219-Article in journal (Refereed) Published
    Abstract [en]

    We examine the existence and properties of certain discrete breathers for a discrete nonlinear Schrodinger model where all but one site are placed in a ring and coupled to the additional central site. The discrete breathers we focus on are stationary solutions mainly localized on one or a few of the ring sites and possibly also the central site. By numerical methods, we trace out and study the continuous families the discrete breathers belong to. Our main result is the discovery of a split bifurcation at a critical value of the coupling between neighboring ring sites. Below this critical value, families form closed loops in a certain parameter space, implying that discrete breathers with and without central-site occupation belong to the same family. Above the split bifurcation the families split up into several separate ones, which bifurcate with solutions with constant ring amplitudes. For symmetry reasons, the families have different properties below the split bifurcation for even and odd numbers of sites. It is also determined under which conditions the discrete breathers are linearly stable. The dynamics of some simpler initial conditions that approximate the discrete breathers are also studied and the parameter regimes where the dynamics remain localized close to the initially excited ring site are related to the linear stability of the exact discrete breathers.

    Place, publisher, year, edition, pages
    AMER PHYSICAL SOC, 2016
    National Category
    Physical Sciences
    Identifiers
    urn:nbn:se:liu:diva-125683 (URN)10.1103/PhysRevE.93.012219 (DOI)000369333600003 ()26871085 (PubMedID)
    Available from: 2016-03-01 Created: 2016-02-29 Last updated: 2017-11-30
  • 239.
    Björk, Jonas
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Chemistry. Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, Faculty of Science & Engineering. Linköping University.
    Thermodynamics of an Electrocyclic Ring-Closure Reaction on Au(111)2016In: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 120, no 38, p. 21716-21721Article in journal (Refereed)
    Abstract [en]

    We have computationally studied the effects of temperature on the reaction pathway of an electrocyclic ring-closure reaction on the Au(111) surface, particularly focusing on thermodynamic aspects of the reaction. The electrocyclic ring closure is accompanied by a series of dehydrogenation steps, and while it is found that temperature, in terms of vibrational entropy and enthalpy, has a reducing effect on most energy barriers, it does not alter the qualitative appreciation of the reaction kinetics. However, it is found that the way the abstracted hydrogen atoms are treated is crucial for the thermodynamics of the reaction. The overall reaction is highly endothermic but becomes thermodynamically favorable due to the entropy gain of the hydrogen byproducts, which desorb associatively from the surface as H2. The study provides new outlooks for the theoretical treatment of reactions related to on-surface synthesis, anticipated to be instructive for future studies.

  • 240.
    Dewandre, Antoine
    et al.
    University of Liege, Belgium.
    Hellman, Olle
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, Faculty of Science & Engineering. CALTECH, CA 91125 USA.
    Bhattacharya, Sandip
    Ruhr University of Bochum, Germany.
    Romero, Aldo H.
    West Virginia University, WV 26506 USA; Benemerita University of Autonoma Puebla, Mexico.
    Madsen, Georg K. H.
    TU Wien, Austria.
    Verstraete, Matthieu J.
    University of Liege, Belgium.
    Two-Step Phase Transition in SnSe and the Origins of its High Power Factor from First Principles2016In: PHYSICAL REVIEW LETTERS, ISSN 0031-9007, Vol. 117, no 27, article id 276601Article in journal (Refereed)
    Abstract [en]

    The interest in improving the thermoelectric response of bulk materials has received a boost after it has been recognized that layered materials, in particular SnSe, show a very large thermoelectric figure of merit. This result has received great attention while it is now possible to conceive other similar materials or experimental methods to improve this value. Before we can now think of engineering this material it is important we understand the basic mechanism that explains this unusual behavior, where very low thermal conductivity and a high thermopower result from a delicate balance between the crystal and electronic structure. In this Letter, we present a complete temperature evolution of the Seebeck coefficient as the material undergoes a soft crystal transformation and its consequences on other properties within SnSe by means of first-principles calculations. Our results are able to explain the full range of considered experimental temperatures.

  • 241.
    Alling, Björn
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, Faculty of Science & Engineering.
    Högberg, Hans
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, Faculty of Science & Engineering.
    Armiento, Rickard
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, Faculty of Science & Engineering.
    Rosén, Johanna
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, Faculty of Science & Engineering.
    Hultman, Lars
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, Faculty of Science & Engineering.
    A theoretical investigation of mixing thermodynamics, age-hardening potential, and electronic structure of ternary (M1-xMxB2)-M-1-B-2 alloys with AlB2 type structure2015In: Scientific Reports, ISSN 2045-2322, E-ISSN 2045-2322, Vol. 5Article in journal (Refereed)
    Abstract [en]

    Transition metal diborides are ceramic materials with potential applications as hard protective thin films and electrical contact materials. We investigate the possibility to obtain age hardening through isostructural clustering, including spinodal decomposition, or ordering-induced precipitation in ternary diboride alloys. By means of first-principles mixing thermodynamics calculations, 45 ternary (M1-xMxB2)-M-1-B-2 alloys comprising (MB2)-B-i (M-i = Mg, Al, Sc, Y, Ti, Zr, Hf, V, Nb, Ta) with AlB2 type structure are studied. In particular Al1-xTixB2 is found to be of interest for coherent isostructural decomposition with a strong driving force for phase separation, while having almost concentration independent a and c lattice parameters. The results are explained by revealing the nature of the electronic structure in these alloys, and in particular, the origin of the pseudogap at E-F in TiB2, ZrB2, and HfB2.

  • 242.
    Mendonca, J. T.
    et al.
    Institute Super Tecn, Portugal.
    Stenflo, Lennart
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, Faculty of Science & Engineering.
    Acoustic-gravity waves in the atmosphere: from Zakharov equations to wave-kinetics2015In: Physica Scripta, ISSN 0031-8949, E-ISSN 1402-4896, Vol. 90, no 5, p. 055001-Article in journal (Refereed)
    Abstract [en]

    We develop a wave-kinetic description of acoustic-gravity (AG) waves in the atmosphere. In our paper the high frequency spectrum of waves is described as a gas of quasi-particles. Starting from the Zakharov-type of equations, where coupling between fast and slow density perturbations is considered, we derive the corresponding wave-kinetic equations, written in terms of an appropriate Wigner function. This provides an alternative description for the nonlinear interaction between the two dispersion branches of the AG waves.

  • 243.
    Shulumba, Nina
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Nanostructured Materials. Linköping University, Faculty of Science & Engineering. University of Saarland, Germany.
    Hellman, Olle
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, Faculty of Science & Engineering. Division of Engineering and Applied Science, California Institute of Technology, Pasadena, California, USA.
    Raza, Zamaan
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, Faculty of Science & Engineering.
    Alling, Björn
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, Faculty of Science & Engineering. Max-Planck-Institut für Eisenforschung GmbH, Düsseldorf, Germany.
    Barrirero, Jennifer
    Linköping University, Department of Physics, Chemistry and Biology. Linköping University, Faculty of Science & Engineering. Functional Materials, Saarland University, Campus D3 3, Saarbrücken, Germany.
    Mücklich, Frank
    Functional Materials, Saarland University, Campus D3 3, Saarbrücken, Germany.
    Abrikosov, Igor
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, Faculty of Science & Engineering. Materials Modeling and Development Laboratory, NUST “MISIS”, Moscow, Russia / LACOMAS Laboratory, Tomsk State University, Tomsk, Russia.
    Odén, Magnus
    Linköping University, Department of Physics, Chemistry and Biology, Nanostructured Materials. Linköping University, Faculty of Science & Engineering.
    Anharmonicity changes the solid solubility of an alloy at high temperatures2015Manuscript (preprint) (Other academic)
    Abstract [en]

    We have developed a method to accurately and efficiently determine the vibrational free energy as a function of temperature and volume for substitutional alloys from first principles. Taking Ti1−xAlxN alloy as a model system, we calculate the isostructural phase diagram by finding the global minimum of the free energy, corresponding to the true equilibrium state of the system. We demonstrate that the anharmonic contribution and temperature dependence of the mixing enthalpy have a decisive impact on the calculated phase diagram of a Ti1−xAlxN alloy, lowering the maximum temperature for the miscibility gap from 6560 K to 2860 K. Our local chemical composition measurements on thermally aged Ti0.5Al0.5N alloys agree with the calculated phase diagram.

  • 244.
    Johansson, Magnus
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, Faculty of Science & Engineering.
    Jason, Peter
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, Faculty of Science & Engineering.
    Breather mobility and the Peierls-Nabarro potential: brief review and recent progress2015In: Quodons in Mica: nonlinear localized travelling excitations in crystals / [ed] Juan F. R. Archilla, Noé Jiménez, Victor J. Sánchez-Morcillo, Luis M. García-Raffi, Cham: Springer, 2015, p. 147-178Chapter in book (Refereed)
    Abstract [en]

    The question whether a nonlinear localized mode (discrete soliton/breather) can be mobile in a lattice has a standard interpretation in terms of the Peierls-Nabarro (PN) potential barrier. For the most commonly studied cases, the PN barrier for strongly localized solutions becomes large, rendering these essentially immobile. Several ways to improve the mobility by reducing the PN-barrier have been proposed during the last decade, and the first part gives a brief review of such scenarios in 1D and 2D. We then proceed to discuss two recently discovered novel mobility scenarios. The first example is the 2D Kagome lattice, where the existence of a highly degenerate, flat linear band allows for a very small PN-barrier and mobility of highly localized modes in a small-power regime. The second example is a 1D waveguide array in an active medium with intrinsic (saturable) gain and damping, where exponentially localized, travelling discrete dissipative solitons may exist as stable attractors. Finally, using the framework of an extended Bose-Hubbard model, we show that while quantum fluctuations destroy the mobility of slowly moving, strongly localized classical modes, coherent mobility of rapidly moving states survives even in a strongly quantum regime

  • 245.
    Yu Nikonov, A.
    et al.
    National Research Tomsk State University, Russia; Institute Strength Phys and Mat Science SB RAS, Russia.
    Zharmukhambetova, A. M.
    National Research Tomsk State University, Russia.
    Skripnyak, N. V.
    National Research Tomsk State University, Russia.
    Ponomareva, A. V.
    National Research University of Technology MISIS, Russia.
    Abrikosov, Igor
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, Faculty of Science & Engineering. National Research Tomsk State University, Russia; National Research University of Technology MISIS, Russia.
    Barannikova, S. A.
    National Research Tomsk State University, Russia; Institute Strength Phys and Mat Science SB RAS, Russia.
    Dmitriev, A. I.
    National Research Tomsk State University, Russia; Institute Strength Phys and Mat Science SB RAS, Russia; National Research Tomsk Polytech University, Russia.
    Calculation of Mechanical Properties of BCC Ti-Nb Alloys2015In: INTERNATIONAL CONFERENCE ON ADVANCED MATERIALS WITH HIERARCHICAL STRUCTURE FOR NEW TECHNOLOGIES AND RELIABLE STRUCTURES 2015, AMER INST PHYSICS , 2015, Vol. 1683, no 020165Conference paper (Refereed)
    Abstract [en]

    We have calculated mechanical properties of bcc Ti-Nb alloys in the framework of the first-principles approach using the exact muffin-tin orbital method. The results obtained quantitatively correlate well with known experimental data and can be used in order to design new materials based on of Ti alloys intended for various applications, e.g. for bio-medical applications.

  • 246.
    Sernelius, Bo E.
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, Faculty of Science & Engineering.
    Casimir effects in systems containing 2D layers such as graphene and 2D electron gases2015In: Journal of Physics: Condensed Matter, ISSN 0953-8984, E-ISSN 1361-648X, Vol. 27, no 21, p. 214017-Article in journal (Refereed)
    Abstract [en]

    We present a variety of methods to derive the Casimir interaction in planar systems containing2D layers. Examples where this can be of use is graphene, graphene-like layers and 2Delectron gases. We present results for two free standing layers and for one layer above asubstrate. The results can easily be extended to systems with a larger number of layers.

  • 247.
    Puglisi, Donatella
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, The Institute of Technology.
    Eriksson, Jens
    Linköping University, Department of Physics, Chemistry and Biology, Applied Sensor Science. Linköping University, The Institute of Technology.
    Bur, Christian
    Linköping University, Department of Physics, Chemistry and Biology, Applied Sensor Science. Linköping University, The Institute of Technology. Saarland University, Lab for Measurement Technology, Germany.
    Schuetze, Andreas
    Saarland University, Germany.
    Lloyd Spetz, Anita
    Linköping University, Department of Physics, Chemistry and Biology, Applied Sensor Science. Linköping University, The Institute of Technology.
    Andersson, Mike
    Linköping University, Department of Physics, Chemistry and Biology, Applied Sensor Science. Linköping University, The Institute of Technology.