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  • 101.
    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.
    Olovsson, Weine
    Linköping University, Faculty of Science & Engineering. Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics.
    Abrikosov, Igor
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, Faculty of Science & Engineering.
    Origin of the core-level binding energy shifts in Au nanoclusters2017In: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 95, no 24, article id 245402Article in journal (Refereed)
    Abstract [en]

    We investigate the shifts of the core-level binding energies in small gold nanoclusters by using ab initio density-functional-theory calculations. The shift of the 4f states is calculated for magic-number nanoclusters in a wide range of sizes and morphologies. We find a nonmonotonous behavior of the core-level shift in nanoclusters depending on the size. We demonstrate that there are three main contributions to the Au 4f shifts, which depend sensitively on the interatomic distances, coordination, and quantum confinement. They are identified and explained by the change of the on-site electrostatic potential.

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  • 102.
    Tasnadi, Ferenc
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, Faculty of Science & Engineering.
    Bock, Florian
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, Faculty of Science & Engineering.
    Ponomareva, Alena V
    NUST MISIS, Russia.
    Bykov, Maxim
    Univ Bayreuth, Germany.
    Khandarkhaeva, Saiana
    Univ Bayreuth, Germany; Univ Bayreuth, Germany.
    Dubrovinsky, Leonid
    Univ Bayreuth, Germany.
    Abrikosov, Igor
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, Faculty of Science & Engineering. NUST MISIS, Russia.
    Thermodynamic and electronic properties of ReN2 polymorphs at high pressure2021In: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 104, no 17, article id 184103Article in journal (Refereed)
    Abstract [en]

    The high-pressure synthesis of rhenium nitride pernitride with a crystal structure that is unusual for transition metal dinitrides and high values of hardness and bulk modulus attracted significant attention to this system. We investigate the thermodynamic and electronic properties of the P2(1)/c phase of ReN2 and compare them with two other polytypes, the C2/m and P4/mbm phases, suggested in the literature. Our calculations of the formation enthalpy at zero temperature show that the former phase is the most stable of the three up to a pressure p = 170 GPa, followed by the stabilization of the P4/mbm phase at higher pressure. The theoretical prediction is confirmed by diamond anvil cell synthesis of the P4/mbm ReN2 at approximate to 175 GPa. Considering the effects of finite temperature in the quasiharmonic approximation at p = 100 GPa we demonstrate that the P2(1)/c phase has the lowest free energy of formation at least up to 1000 K. Our analysis of the pressure dependence of the electronic structure of rhenium nitride pernitride shows the presence of two electronic topological transitions around 18 GPa, when the Fermi surface changes its topology due to the appearance of an electron pocket at the high-symmetry Y-2 point of the Brillouin zone while the disruption of the neck takes place slightly off from the Gamma-A line.

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  • 103.
    Thore, Andreas
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, Faculty of Science & Engineering.
    Dahlqvist, Martin
    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.
    Rosén, Johanna
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, Faculty of Science & Engineering.
    Magnetic exchange interactions and critical temperature of the nanolaminate Mn2GaC from first-principles supercell methods2016In: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 93, no 5Article in journal (Refereed)
    Abstract [en]

    In this work, we employ and critically evaluate a first-principles approach based on supercell calculations for predicting the magnetic critical order-disorder temperature 𝑇𝑐 . As a model material we use the recently discovered nanolaminate Mn2GaC.

    First, we derive the exchange interaction parameters 𝐽𝑖𝑗 between pairs of Mn atoms on sites 𝑖 and 𝑗 of the bilinear Heisenberg Hamiltonian using the novel magnetic direct cluster averaging method (MDCA), and then compare the 𝐽’s from the MDCA calculations to the same parameters calculated using the Connolly-Williams method. We show that the two methods yield closely matching results, but observe that the MDCA method is computationally less effective when applied to highly ordered phases such as Mn2GaC.

    Secondly, Monte Carlo simulations are used to derive the magnetic energy, specific heat, and 𝑇𝑐 . For Mn2GaC, we find 𝑇𝑐 = 660 K. The uncertainty in the calculated 𝑇𝑐 caused by possible uncertainties in the 𝐽’s is discussed and exemplified in our case by an analysis of the impact of the statistical uncertainties of the MDCA-derived 𝐽’s, resulting in a 𝑇𝑐 distribution with a standard deviation of 133 K.

  • 104.
    Tidholm, Johan
    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.
    Shulumba, Nina
    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.
    Tasnadi, Ferenc
    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.
    Temperature dependence of the Kohn anomaly in bcc Nb from first-principles self-consistent phonon calculations2020In: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 101, no 11, article id 115119Article in journal (Refereed)
    Abstract [en]

    Using ab initio calculations, we have analyzed the influence of anharmonic effects on the electronic structure and the phonon-dispersion relations of body-centered-cubic (bcc) niobium (Nb) and investigated the temperature dependence of the Kohn anomaly in this metal. A comparison of the results obtained in the framework of the temperature-dependent effective potential method with those derived within the quasiharmonic approximation demonstrates the importance of the explicit treatment of the finite-temperature effects upon the theoretical description of bcc Nb lattice dynamics. In agreement with experimental results, the inclusion of anharmonic vibrations in our calculations leads to the disappearance of the Kohn anomaly for the acoustic mode in a vicinity of the Gamma point with increasing temperature. Moreover, the calculated phonon self-energy indicates that the origin of the temperature dependence is related to the change of the electronic structure. We have calculated the temperature dependence of the electronic spectral function and analyzed the Fermi surface of Nb. A significant temperature-induced smearing of the electronic states has been identified as the origin of the disappearance of the Kohn anomaly in Nb at elevated temperature.

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  • 105.
    Trybel, Florian
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, Faculty of Science & Engineering. Univ Bayreuth, Germany.
    Meier, Thomas
    Univ Bayreuth, Germany; Ctr High Pressure Sci & Technol Adv Res HPSTAR, Peoples R China.
    Wang, Biao
    Univ Bayreuth, Germany; Univ Oxford, England.
    Steinle-Neumann, Gerd
    Univ Bayreuth, Germany.
    Absence of proton tunneling during the hydrogen-bond symmetrization in delta-AlOOH2021In: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 104, no 10, article id 104311Article in journal (Refereed)
    Abstract [en]

    delta-AlOOH is of significant crystallochemical interest due to a subtle structural transition near 10 GPa from a P2(1) nm to a Pnnm structure, the nature and origin of hydrogen disorder, the symmetrization of the O-H center dot center dot center dot O hydrogen bond and their interplay. We perform a series of density functional theory-based simulations in combination with high-pressure nuclear magnetic resonance (NMR) experiments on delta-AlOOH up to 40 GPa with the goal to better characterize the hydrogen potential and therefore the nature of hydrogen disorder. Simulations predict a phase transition in agreement with our NMR experiments at 10 - 11 GPa and hydrogen bond symmetrization at 14.7 GPa. Calculated hydrogen potentials do not show any double-well character and there is no evidence for proton tunneling in our NMR data.

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  • 106.
    Tureson, Nina
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, Faculty of Science & Engineering.
    Marteau, Marc
    Univ Poitiers, France.
    Cabioch, Thierry
    Univ Poitiers, France.
    Van Nong, Ngo
    Tech Univ Denmark, Denmark.
    Jensen, Jens
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, Faculty of Science & Engineering.
    Lu, Jun
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, Faculty of Science & Engineering.
    Greczynski, Grzegorz
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, Faculty of Science & Engineering.
    Fournier, Daniele
    Sorbonne Univ, France.
    Singh, Niraj
    Indian Inst Technol Mandi, India.
    Soni, Ajay
    Indian Inst Technol Mandi, India.
    Belliard, Laurent
    Sorbonne Univ, France.
    Eklund, Per
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, Faculty of Science & Engineering.
    Le Febvrier, Arnaud
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, Faculty of Science & Engineering.
    Effect of ion-implantation-induced defects and Mg dopants on the thermoelectric properties of ScN2018In: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 98, no 20, article id 205307Article in journal (Refereed)
    Abstract [en]

    For applications in energy harvesting and environmentally friendly cooling, and for power sources in remote or portable applications, it is desired to enhance the efficiency of thermoelectric materials. One strategy consists of reducing the thermal conductivity while increasing or retaining the thermoelectric power factor. An approach to achieve this is doping to enhance the Seebeck coefficient and electrical conductivity, while simultaneously introducing defects in the materials to increase phonon scattering. Here, we use Mg ion implantation to induce defects in epitaxial ScN (111) films. The films were implanted with Mg+ ions with different concentration profiles along the thickness of the film, incorporating 0.35 to 2.2 at. % of Mg in ScN. Implantation at high temperature (600 degrees C), with few defects due to the temperature, does not substantially affect the thermal conductivity compared to a reference ScN. Samples implanted at room temperature, in contrast, exhibited a reduction of the thermal conductivity by a factor of 3. The sample doped with 2.2 at. % of Mg also showed an increased power factor after implantation. This paper thus shows the effect of ion-induced defects on thermal conductivity of ScN films. High-temperature implantation allows the defects to be annealed out during implantation, while the defects are retained for room-temperature implanted samples, allowing for a drastic reduction in thermal conductivity.

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  • 107.
    Xu, Bin
    et al.
    Soochow Univ, Peoples R China; Univ Arkansas, AR 72701 USA; Univ Arkansas, AR 72701 USA.
    Hellman, Olle
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, Faculty of Science & Engineering.
    Bellaiche, L.
    Univ Arkansas, AR 72701 USA.
    Order-disorder transition in the prototypical antiferroelectric PbZrO32019In: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 100, no 2, article id 020102Article in journal (Refereed)
    Abstract [en]

    The prototypical antiferroelectric PbZrO3 has several unsettled questions, such as the nature of the antiferroelectric transition, a possible intermediate phase, and the microscopic origin of the Pbam ground state. Using first-principles calculations, we show that no phonon becomes truly soft at the cubic-to-Pbam transition temperature, and the order-disorder character of this transition is clearly demonstrated based on molecular dynamics simulations and potential energy surfaces. The out-of-phase octahedral tilting is an important degree of freedom, which can collaborate with other phonon distortions and form a complex energy landscape with multiple minima Candidates of the possible intermediate phase are suggested based on the calculated kinetic barriers between energy minima, and the development of a first-principles-based effective Hamiltonian. The use of this latter scheme further reveals that specific bilinear interactions between local dipoles and octahedral tiltings play a major role in the formation of the Pbam ground state, which contrasts with most of the previous explanations.

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  • 108.
    Yang, Jinpeng
    et al.
    Yangzhou Univ, Peoples R China; Inst Mol Sci, Japan.
    Meissner, Matthias
    Inst Mol Sci, Japan.
    Yamaguchi, Takuma
    Inst Mol Sci, Japan.
    Xi, Bin
    Yangzhou Univ, Peoples R China.
    Takahashi, Keishi
    Chiba Univ, Japan.
    Abdullah, Shed
    Chiba Univ, Japan.
    Liu, Xianjie
    Linköping University, Department of Science and Technology, Laboratory of Organic Electronics. Linköping University, Faculty of Science & Engineering.
    Yoshida, Hiroyuki
    Chiba Univ, Japan.
    Fahlman, Mats
    Linköping University, Department of Science and Technology, Laboratory of Organic Electronics. Linköping University, Faculty of Science & Engineering.
    Kera, Satoshi
    Inst Mol Sci, Japan.
    Temperature-dependent band structure evolution determined by surface geometry in organic halide perovskite single crystals2020In: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 102, no 24, article id 245101Article in journal (Refereed)
    Abstract [en]

    Organic halide perovskites have attracted much attention due to their potential applications in optoelectronic devices. Since the generally higher flexibility compared to their inorganic counterparts, their structures are prone to be more sensitive toward external effects, where the fundamental understanding of their band structure evolutions is still inconclusive. In this study, different electronic structure evolutions of perovskite single crystals are found via angle-resolved photoelectron spectroscopy: (i) Unchanged top valence band (VB) dispersions under different temperatures can be found in the CH3NH3PbI3. (ii) Phase transitions induced the evolution of top VB dispersions, and even a top VB splitting with Rashba effects can be observed in the CH3NH3PbBr3. Combined with low-energy electron diffraction, metastable atom electron spectroscopy, and density functional theory calculation, we confirm that different band structure evolutions observed in these two perovskite single crystals originated from the cleaved top surface layers, where the different surface geometries with CH3NH3+-I in CH3NH3PbI3 and Pb-Br in CH3NH3PbBr3 are responsible for finding band dispersion change and appearance of the Rashba-type splitting. Such findings suggest that the top surface layer in organic halide perovskites should be carefully considered to create functional interfaces for developing perovskite devices.

  • 109.
    Zhao, Q.X.
    et al.
    Physical Electronics and Photonics, Department of Physics, Chalmers University of Technology and University of Göteborg, Sweden.
    Willander, M.
    Physical Electronics and Photonics, Department of Physics, Chalmers University of Technology and University of Göteborg, Sweden.
    Bergman, Peder
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials.
    Holtz, Per-Olof
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials.
    Lu, W.
    National Laboratory for Infrared Physics, Shanghai Institute of Technical Physics, Chinese Academy of Sciences, Shanghai China.
    Shen, S.C.
    National Laboratory for Infrared Physics, Shanghai Institute of Technical Physics, Chinese Academy of Sciences, Shanghai China.
    Dynamic properties of radiative recombination in p-type d-doped layers in GaAs2001In: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 63, article id 125337Article in journal (Refereed)
    Abstract [en]

     We present an optical study of thin Zn-doped GaAs layers embedded in bulk GaAs, grown by metal-organic vapor-phase-epitaxy by means of stationary and time-resolved optical spectroscopy. The concentration of the Zn acceptors was aimed at 2×1020/cm3 in 4-nm-wide doping regions. The intensity of the optical radiative transition (so called the F emission) appearing in photoluminescence spectra was found to be related to holes confined at doping regions. The F emission shows a strong dependence on excitation intensity and temperature. The energy position varies from 1.46 to 1.49 eV as the excitation density changes from about 40 mW/cm2 to 23 W/cm2. The dynamic properties of the F-emission band have been studied by time-resolved spectroscopy. The F emission shows a nonexponential decay character. The decay time of the F emission exhibits a strong dependence on the detection energy within the F-emission band. The decay time becomes longer as the detection energy is redshifted.

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