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Spin polarization in open quantum dots
Linköping University, Department of Science and Technology. Linköping University, The Institute of Technology.
Linköping University, Department of Science and Technology. Linköping University, The Institute of Technology.
2006 (English)In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 73, no 3, 035319- p.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.

Place, publisher, year, edition, pages
2006. Vol. 73, no 3, 035319- p.
Keyword [en]
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: urn:nbn:se:liu:diva-13472DOI: 10.1103/PhysRevB.73.035319OAI: oai:DiVA.org:liu-13472DiVA: diva2:20827
Available from: 2005-11-24 Created: 2005-11-24 Last updated: 2017-12-13Bibliographically approved
In thesis
1. Spin splitting in open quantum dots and related systems
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. 42 p.
Series
Linköping Studies in Science and Technology. Thesis, ISSN 0280-7971 ; 1210
Keyword
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
2. Quantum transport and spin effects in lateral semiconductor nanostructures and graphene
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. 66 p.
Series
Linköping Studies in Science and Technology. Dissertations, ISSN 0345-7524 ; 1202
Keyword
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

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Evaldsson, MartinZozoulenko, Igor V.

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