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Spin splitting in open quantum dots and related systems
Linköping University, Department of Science and Technology. Linköping University, The Institute of Technology.
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 [en]
mesoscopic systems, 2DEG, ballistic transport, quantum dots, spin-polarised transport in quantum dots, spontanueous spin-splitting
National Category
Condensed Matter Physics
Identifiers
URN: urn:nbn:se:liu:diva-4939ISBN: 91-85457-69-8 (print)OAI: oai:DiVA.org:liu-4939DiVA: diva2:20828
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
List of papers
1. Spin splitting in open quantum dots
Open this publication in new window or tab >>Spin splitting in open quantum dots
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2004 (English)In: Europhysics letters, ISSN 0295-5075, Vol. 68, no 2, 261-267 p.Article in journal (Refereed) Published
Abstract [en]

We demonstrate that the magnetoconductance of small lateral quantum dots in the strongly coupled regime (i.e. when the leads can support one or more propagating modes) shows a pronounced splitting of the conductance peaks and dips which persists over a wide range of magnetic fields (from zero field to the edge-state regime) and is virtually independent of the magnetic field strength. Our numerical analysis of the conductance based on the Hubbard Hamiltonian demonstrates that this is essentially a many-body/spin effect that can be traced to a splitting of degenerate levels in the corresponding closed dot. The above effect in open dots can be regarded as a counterpart of the Coulomb-blockade effect in weakly coupled dots, with the difference, however, that the splitting of the peaks originates from interactions between electrons of opposite spin.

National Category
Engineering and Technology
Identifiers
urn:nbn:se:liu:diva-13470 (URN)10.1209/epl/i2004-10189-2 (DOI)
Available from: 2005-11-24 Created: 2005-11-24 Last updated: 2009-02-11Bibliographically approved
2. Quantum antidot as a controllable spin injector and spin filter
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, Vol. 85, no 15, 3136-3138 p.Article 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: 2009-06-09Bibliographically approved
3. Spin polarization in open quantum dots
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, 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.

Keyword
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: 2009-02-19Bibliographically approved

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Evaldsson, Martin

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