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Evaldsson, Martin
Publications (10 of 11) Show all publications
Evaldsson, M., Zozoulenko, I. V., Xu, H. & Heinzel, T. (2008). Edge disorder induced Anderson localization and conduction gap in graphene nanoribbons. Physical Review B. Condensed Matter and Materials Physics, 78(16), 161407
Open this publication in new window or tab >>Edge disorder induced Anderson localization and conduction gap in graphene nanoribbons
2008 (English)In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 78, no 16, p. 161407-Article in journal (Refereed) Published
Abstract [en]

We study the effect of the edge disorder on the conductance of the graphene nanoribbons (GNRs).We find that only very modest edge disorder is sufficient to induce the conduction energy gap inthe otherwise metallic GNRs and to lift any difference in the conductance between nanoribbonsof different edge geometry. We relate the formation of the conduction gap to the pronounced edgedisorder induced Anderson-type localization which leads to the strongly enhanced density of states atthe edges, formation of surface-like states and to blocking of conductive paths through the ribbons.

Place, publisher, year, edition, pages
American Physical Society, 2008
National Category
Physical Sciences
Identifiers
urn:nbn:se:liu:diva-14778 (URN)10.1103/PhysRevB.78.161407 (DOI)
Available from: 2008-09-24 Created: 2008-09-24 Last updated: 2017-12-13Bibliographically approved
Xu, H., Heinzel, T., Evaldsson, M. & Zozoulenko, I. V. (2008). Magnetic barriers in graphene nanoribbons: Theoretical study of transport properties. Physical Review B. Condensed Matter and Materials Physics, 77(24), 245401-
Open this publication in new window or tab >>Magnetic barriers in graphene nanoribbons: Theoretical study of transport properties
2008 (English)In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 77, no 24, p. 245401-Article in journal (Refereed) Published
Abstract [en]

A theoretical study of the transport properties of zigzag and armchair graphene nanoribbons with a magnetic barrier on top is presented. The magnetic barrier modifies the energy spectrum of the nanoribbons locally, which results in an energy shift of the conductance steps toward higher energies. The magnetic barrier also induces Fabry–Pérot-type oscillations, provided the edges of the barrier are sufficiently sharp. The lowest propagating state present in zigzag and metallic armchair nanoribbons prevents confinement of the charge carriers by the magnetic barrier. Disordered edges in nanoribbons tend to localize the lowest propagating state, which get delocalized in the magnetic barrier region. Thus, in sharp contrast to the case of two-dimensional graphene, the charge carriers in graphene nanoribbons cannot be confined by magnetic barriers. We also present a method based on the Green's function technique for the calculation of the magnetosubband structure, Bloch states and magnetoconductance of the graphene nanoribbons in a perpendicular magnetic field. Utilization of this method greatly facilitates the conductance calculations, because, in contrast to existing methods, the present method does not require self-consistent calculations for the surface Green's function.

National Category
Physical Sciences
Identifiers
urn:nbn:se:liu:diva-14777 (URN)10.1103/PhysRevB.77.245401 (DOI)
Available from: 2008-09-24 Created: 2008-09-24 Last updated: 2017-12-13
Evaldsson, M. (2008). Quantum transport and spin effects in lateral semiconductor nanostructures and graphene. (Doctoral dissertation). Linköping: Linköping University Electronic Press
Open this publication in new window or tab >>Quantum transport and spin effects in lateral semiconductor nanostructures and graphene
2008 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

This thesis studies electron spin phenomena in lateral semi-conductor quantum dots/anti-dots and electron conductance in graphene nanoribbons by numerical modelling. In paper I we have investigated spin-dependent transport through open quantum dots, i.e., dots strongly coupled to their leads, within the Hubbard model. Results in this model were found consistent with experimental data and suggest that spin-degeneracy is lifted inside the dot – even at zero magnetic field.

Similar systems were also studied with electron-electron effects incorporated via Density Functional Theory (DFT) in the Local Spin Density Approximation (LSDA) in paper II and III. In paper II we found a significant spin-polarisation in the dot at low electron densities. As the electron density increases the spin polarisation in the dot gradually diminishes. These findings are consistent with available experimental observations. Notably, the polarisation is qualitatively different from the one found in the Hubbard model.

Paper III investigates spin polarisation in a quantum wire with a realistic external potential due to split gates and a random distribution of charged donors. At low electron densities we recover spin polarisation and a metalinsulator transition when electrons are localised to electron lakes due to ragged potential profile from the donors. In paper IV we propose a spin-filter device based on resonant backscattering of edge states against a quantum anti-dot embedded in a quantum wire. A magnetic field is applied and the spin up/spin down states are separated through Zeeman splitting. Their respective resonant states may be tuned so that the device can be used to filter either spin in a controlled way.

Paper V analyses the details of low energy electron transport through a magnetic barrier in a quantum wire. At sufficiently large magnetisation of the barrier the conductance is pinched off completely. Furthermore, if the barrier is sharp we find a resonant reflection close to the pinch off point. This feature is due to interference between a propagating edge state and quasibond state inside the magnetic barrier.

Paper VI adapts an efficient numerical method for computing the surface Green’s function in photonic crystals to graphene nanoribbons (GNR). The method is used to investigate magnetic barriers in GNR. In contrast to quantum wires, magnetic barriers in GNRs cannot pinch-off the lowest propagating state. The method is further applied to study edge dislocation defects for realistically sized GNRs in paper VII. In this study we conclude that even modest edge dislocations are sufficient to explain both the energy gap in narrow GNRs, and the lack of dependance on the edge structure for electronic properties in the GNRs.

Place, publisher, year, edition, pages
Linköping: Linköping University Electronic Press, 2008. p. 66
Series
Linköping Studies in Science and Technology. Dissertations, ISSN 0345-7524 ; 1202
Keywords
Electronic transport, Spin related phenomena, Quantum dots, Quantum wires, Two-dimensional electron gas, 2DEG, Graphene
National Category
Other Physics Topics Physical Sciences
Identifiers
urn:nbn:se:liu:diva-12410 (URN)978-91-7393-835-8 (ISBN)
Public defence
2008-09-19, K3, Kåkenhus, Campus Norrköping, Linköpings universitet, Norrköping, 10:15 (English)
Opponent
Supervisors
Available from: 2008-09-24 Created: 2008-09-03 Last updated: 2009-03-10Bibliographically approved
Evaldsson, M., Ihnatsenka, S. & Zozoulenko, I. V. (2008). Spin polarization in modulation-doped GaAs quantum wires. Physical Review B. Condensed Matter and Materials Physics, 77(16), 165306-1-165306-7, Article ID 165306.
Open this publication in new window or tab >>Spin polarization in modulation-doped GaAs quantum wires
2008 (English)In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 77, no 16, p. 165306-1-165306-7, article id 165306Article in journal (Refereed) Published
Abstract [en]

We study spin polarization in a split-gate quantum wire focusing on the effect of a realistic smooth potential due to remote donors. Electron interaction and spin effects are included within the density functional theory in the local spin density approximation. We find that depending on the electron density, the spin polarization exhibits qualitatively different features. For the case of relatively high electron density, when the Fermi energy EF exceeds a characteristic strength of a long-range impurity potential Vdonors, the density spin polarization inside the wire is practically negligible and the wire conductance is spin-degenerate. When the density is decreased such that EF approaches Vdonors, the electron density and conductance quickly become spin polarized. With further decrease of the density the electrons are trapped inside the lakes (droplets) formed by the impurity potential and the wire conductance approaches the pinch-off regime. We discuss the limitations of the density functional theory in the local spin density approximation in this regime and compare the obtained results with available experimental data.

Place, publisher, year, edition, pages
American Physical Society, 2008
National Category
Physical Sciences
Identifiers
urn:nbn:se:liu:diva-11757 (URN)10.1103/PhysRevB.77.165306 (DOI)
Note

Original publication: M. Evaldsson, S. Ihnatsenka, and I. V. Zozoulenko, Spin polarization in modulation-doped GaAs quantum wires, 2008, Physical Review B, (77), 165306. http://dx.doi.org/10.1103/PhysRevB.77.165306. Copyright: The America Physical Society, http://prb.aps.org/

Available from: 2008-05-08 Created: 2008-05-08 Last updated: 2018-09-06Bibliographically approved
Xu, H., Heinzel, T., Evaldsson, M., Ihnatsenka, S. & Zozoulenko, I. (2007). Resonant reflection at magnetic barriers in quantum wires. Physical Review B. Condensed Matter and Materials Physics, 75(20), 205301-
Open this publication in new window or tab >>Resonant reflection at magnetic barriers in quantum wires
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2007 (English)In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 75, no 20, p. 205301-Article in journal (Refereed) Published
Abstract [en]

The conductance of a quantum wire containing a single magnetic barrier is studied numerically by means of the recursive Green's function technique. For sufficiently strong and localized barriers, Fano-type reflection resonances are observed close to the pinch-off regime. They are attributed to a magnetoelectric vortex-type quasibound state inside the magnetic barrier that interferes with an extended mode outside. We, furthermore, show that disorder can substantially modify the residual conductance around the pinch-off regime.

National Category
Physical Sciences
Identifiers
urn:nbn:se:liu:diva-14775 (URN)10.1103/PhysRevB.75.205301 (DOI)
Available from: 2008-09-24 Created: 2008-09-24 Last updated: 2017-12-13
Evaldsson, M. & Zozoulenko, I. V. (2006). Spin polarization in open quantum dots. Physical Review B. Condensed Matter and Materials Physics, 73(3), 035319-
Open this publication in new window or tab >>Spin polarization in open quantum dots
2006 (English)In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 73, no 3, p. 035319-Article in journal (Refereed) Published
Abstract [en]

We investigate coherent transport through open lateral quantum dots using recursive Green's function technique, incorporating exchange-correlation effects within the density functional theory (DFT) in the local spin-density approximation. At low electron densities the current is spin polarized and electron density in the dot shows a strong spin polarization. As the electron density increases the spin polarization in the dot gradually diminishes. These findings are consistent with available experimental observations. Results of our DFT-based modeling indicate that utilization of the simplified approaches that use phenomenological parameters and/or model Hamiltonians might not be always reliable for theoretical predictions as well as interpretations of the experiments.

Keywords
spin polarised transport, semiconductor quantum dots, Green's function methods, exchange interactions (electron), density functional theory, electronic density of states
National Category
Physical Sciences
Identifiers
urn:nbn:se:liu:diva-13472 (URN)10.1103/PhysRevB.73.035319 (DOI)
Available from: 2005-11-24 Created: 2005-11-24 Last updated: 2017-12-13Bibliographically approved
Zozoulenko, I. & Evaldsson, M. (2005). Quantum antidot as a controllable spin injector and spin filter. In: International Conference on the Physics of Semiconductors,2004 (pp. 1395). Melville, New York: American Institute of Physics
Open this publication in new window or tab >>Quantum antidot as a controllable spin injector and spin filter
2005 (English)In: International Conference on the Physics of Semiconductors,2004, Melville, New York: American Institute of Physics , 2005, p. 1395-Conference paper, Published paper (Refereed)
Place, publisher, year, edition, pages
Melville, New York: American Institute of Physics, 2005
National Category
Engineering and Technology
Identifiers
urn:nbn:se:liu:diva-32316 (URN)18207 (Local ID)18207 (Archive number)18207 (OAI)
Available from: 2009-10-09 Created: 2009-10-09
Evaldsson, M., Zozoulenko, I., Ciorga, M., Zawadzki, P. & Sachrajda, A. (2005). Spin Splitting in open quantum dots. In: International Conference on the Physics of Semiconductors,2004 (pp. 1413). Melville, New York: American Institute of Physics
Open this publication in new window or tab >>Spin Splitting in open quantum dots
Show others...
2005 (English)In: International Conference on the Physics of Semiconductors,2004, Melville, New York: American Institute of Physics , 2005, p. 1413-Conference paper, Published paper (Refereed)
Place, publisher, year, edition, pages
Melville, New York: American Institute of Physics, 2005
National Category
Engineering and Technology
Identifiers
urn:nbn:se:liu:diva-32315 (URN)18206 (Local ID)18206 (Archive number)18206 (OAI)
Available from: 2009-10-09 Created: 2009-10-09
Evaldsson, M. (2005). Spin splitting in open quantum dots and related systems. (Licentiate dissertation). : Institutionen för teknik och naturvetenskap
Open this publication in new window or tab >>Spin splitting in open quantum dots and related systems
2005 (English)Licentiate thesis, comprehensive summary (Other academic)
Abstract [en]

This thesis addresses electron spin phenomena in semi-conductor quantum dots/anti-dots from a computational perspective. In the first paper (paper I) we have studied spin-dependent transport through open quantum dots, i.e., dots strongly coupled to their leads, within the Hubbard model. Results in this model were found consistent with experimental data and suggest that spin-degeneracy is lifted inside the dot – even at zero magnetic field.

Similar systems were also studied with electron-electron effects incorporated via Density Functional Theory (DFT) in paper III. Within DFT we found a significant spin-polarisation in the dot at low electron densities. As the electron density increases the spin polarisation in the dot gradually diminishes. These findings are consistent with available experimental observations. Notably, the polarisation is qualitatively different from the one found in the Hubbard model – this indicates that the simplified approach to electronelectron interaction in the Hubbard model might not always be reliable.

In paper II we propose a spin-filter device based on resonant backscattering of edge states against a quantum anti-dot embedded in a quantum wire. A magnetic field is applied and the spin up/spin down states are separated through Zeeman splitting. Their respective resonant states may be tuned so that the device can be used to filter either spin in a controlled way.

Place, publisher, year, edition, pages
Institutionen för teknik och naturvetenskap, 2005. p. 42
Series
Linköping Studies in Science and Technology. Thesis, ISSN 0280-7971 ; 1210
Keywords
mesoscopic systems, 2DEG, ballistic transport, quantum dots, spin-polarised transport in quantum dots, spontanueous spin-splitting
National Category
Condensed Matter Physics
Identifiers
urn:nbn:se:liu:diva-4939 (URN)91-85457-69-8 (ISBN)
Presentation
2005-12-12, K3, Täppan, Campus Norrköping, Linköpings universitet, Norrköping, 10:15 (English)
Opponent
Supervisors
Note
Report code: LIU-Tek-Lic 2005:65Available from: 2005-11-24 Created: 2005-11-24
Zozoulenko, I. V. & Evaldsson, M. (2004). Quantum antidot as a controllable spin injector and spin filter. Applied Physics Letters, 85(15), 3136-3138
Open this publication in new window or tab >>Quantum antidot as a controllable spin injector and spin filter
2004 (English)In: Applied Physics Letters, ISSN 0003-6951, E-ISSN 1077-3118, Vol. 85, no 15, p. 3136-3138Article in journal (Refereed) Published
Abstract [en]

We propose a device based on an antidot embedded in a narrow quantum wire in the edge-state regime, that can be used to inject and/or control spin-polarized current. The operational principle of the device is based on the effect of resonant backscattering from one edge state into another through localized quasibound states, combined with the effect of Zeeman splitting of the quasibound states in sufficiently high magnetic field. We outline the device geometry, present detailed quantum-mechanical transport calculations, and suggest a possible scheme to test the device performance and functionality.

National Category
Physical Sciences
Identifiers
urn:nbn:se:liu:diva-13471 (URN)10.1063/1.1804249 (DOI)
Available from: 2005-11-24 Created: 2005-11-24 Last updated: 2017-12-13Bibliographically approved
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