Tailoring semiconductor spintronics devices [Elektronische Ressource] : tools for the creation and control of spins in two-dimensional electron gases / Matthias Scheid
156 Pages
English
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Tailoring semiconductor spintronics devices [Elektronische Ressource] : tools for the creation and control of spins in two-dimensional electron gases / Matthias Scheid

Downloading requires you to have access to the YouScribe library
Learn all about the services we offer
156 Pages
English

Description

In recent years the research field of semiconduc-tor spintronics has attracted considerable atten-tion. This interest was fueled by the prospect of spin-based devices, which could possess en-hanced functionalities compared to conventional charge-based microelectronics. However, in or-der to realize the building blocks for semiconduc-tor spintronics devices a number of fundamental obstacles have to be overcome. To this end, this thesis discusses several spin- related phenomena in two-dimensional electron gases, which can either be exploited as sources for spin currents/accumulations or which can be used for the efficient control of those spins. To Matthias Scheidbe specific, it deals with coherent electron trans-port through wire geometries in the presence of Tailoring semiconductor spin-orbit interaction and/or magnetic fields. For the numerical calculations a powerful quantum spintronics devices: transport code was used. The topics investigated in this thesis include spin ratchets, the phenom- Tools for the creation and enon of current-induced spin accumulation and finally quantum interference spin phenomena in control of spins in two-disordered systems.

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Published 01 January 2010
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In recent years the research field of semiconduc-
tor spintronics has attracted considerable atten-
tion. This interest was fueled by the prospect
of spin-based devices, which could possess en-
hanced functionalities compared to conventional
charge-based microelectronics. However, in or-
der to realize the building blocks for semiconduc-
tor spintronics devices a number of fundamental
obstacles have to be overcome.
To this end, this thesis discusses several spin-
related phenomena in two-dimensional electron
gases, which can either be exploited as sources
for spin currents/accumulations or which can be
used for the efficient control of those spins. To Matthias Scheid
be specific, it deals with coherent electron trans-
port through wire geometries in the presence of
Tailoring semiconductor spin-orbit interaction and/or magnetic fields. For
the numerical calculations a powerful quantum spintronics devices: transport code was used. The topics investigated
in this thesis include spin ratchets, the phenom- Tools for the creation and enon of current-induced spin accumulation and
finally quantum interference spin phenomena in control of spins in two-
disordered systems.
dimensional electron gases
1 2
ISBN 978-3-86845-047-7
Matthias Scheid Dissertationsreihe Physik - Band 12Matthias Scheid
Tailoring semiconductor
spintronics devices:
Tools for the creation and
control of spins in two-
dimensional electron gasesTailoring semiconductor spintronics devices:
Tools for the creation and control
of spins in two-dimensional electron gases
Dissertation zur Erlangung des Doktorgrades der Naturwissenschaften (Dr. rer. nat.)
der naturwissenschaftlichen Fakultät II - Physik der Universität Regensburg
vorgelegt von
Matthias Scheid
aus Regensburg
September 2009
Die Arbeit wurde von Prof. Dr. Klaus Richter angeleitet.
Das Promotionsgesuch wurde am 24.09.2009 eingereicht.
Das Kolloquium fand am 03.02.2010 statt.
Prüfungsausschuss: Vorsitzender: Prof. Dr. Christian Back
1. Gutachter: Prof. Dr. Klaus Richter
2. Gutachter: Prof. Dr. Milena Grifoni
weiterer Prüfer: Prof. Dr. Ingo Morgenstern
Dissertationsreihe der Fakultät für Physik der Universität Regensburg,
Band 12
Herausgegeben vom Präsidium des Alumnivereins der Physikalischen Fakultät:
Klaus Richter, Andreas Schäfer, Werner Wegscheider, Dieter WeissMatthias Scheid
Tailoring semiconductor
spintronics devices:
Tools for the creation and
control of spins in two-
dimensional electron gasesBibliografische Informationen der Deutschen Bibliothek.
Die Deutsche Bibliothek verzeichnet diese Publikation
in der Deutschen Nationalbibliografie. Detailierte bibliografische Daten
sind im Internet über http://dnb.ddb.de abrufbar.
1. Auflage 2010
© 2010 Universitätsverlag, Regensburg
Leibnitzstraße 13, 93055 Regensburg
Konzeption: Thomas Geiger
Umschlagentwurf: Franz Stadler, Designcooperative Nittenau eG
Layout: Matthias Scheid
Druck: Docupoint, Magdeburg
ISBN: 978-3-86845-047-7
Alle Rechte vorbehalten. Ohne ausdrückliche Genehmigung des Verlags ist es
nicht gestattet, dieses Buch oder Teile daraus auf fototechnischem oder
elektronischem Weg zu vervielfältigen.
Weitere Informationen zum Verlagsprogramm erhalten Sie unter:
www.univerlag-regensburg.deTailoring semiconductor spintronics devices:
Tools for the creation and control
of spins in two-dimensional electron gases
Dissertation zur Erlangung des Doktorgrades der Naturwissenschaften (Dr. rer. nat.)
der naturwissenschaftlichen Fakultät II - Physik der Universität Regensburg
vorgelegt von
Matthias Scheid
aus Regensburg
September 2009
Die Arbeit wurde von Prof. Dr. Klaus Richter angeleitet.
Das Promotionsgesuch wurde am 24.09.2009 eingereicht.
Das Kolloquium fand am 03.02.2010 statt.
Prüfungsausschuss: Vorsitzender: Prof. Dr. Christian Back
1. Gutachter: Prof. Dr. Klaus Richter
2. Gutachter: Prof. Dr. Milena Grifoni
weiterer Prüfer: Prof. Dr. Ingo Morgenstern
Dissertationsreihe der Fakultät für Physik der Universität Regensburg,
Band 12
Herausgegeben vom Präsidium des Alumnivereins der Physikalischen Fakultät:
Klaus Richter, Andreas Schäfer, Werner Wegscheider, Dieter WeissPromotionsgesuch eingereicht am: 24.09.2009
Die Arbeit wurde angeleitet von: Prof. Dr. Klaus Richter
Prüfungsausschuss: Vorsitzender: Prof. Dr. Christian Back
1. Gutachter: Prof. Dr. Klaus Richter
2. Gutachter: Prof. Dr. Milena Grifoni
weiterer Prüfer: Prof. Dr. Ingo MorgensternContents
1 Introduction 1
2 Spin dependent transport in nanostructures 7
2.1 Two-dimensional electron gases . . . . . . . . . . . . . . . . . . . . . . 9
2.1.1 Magnetic fields . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
2.1.2 Spin-orbit interaction . . . . . . . . . . . . . . . . . . . . . . . . 11
2.2 Landauer-Bu¨ttiker formalism . . . . . . . . . . . . . . . . . . . . . . . . 18
2.2.1 Scattering approach . . . . . . . . . . . . . . . . . . . . . . . . . 18
2.2.2 Charge and spin currents . . . . . . . . . . . . . . . . . . . . . . 21
2.3 Green’s function formalism for electron transport in nanostructures . . 26
2.3.1 Basic definitions . . . . . . . . . . . . . . . . . . . . . . . . . . . 26
2.3.2 Numerical calculation scheme . . . . . . . . . . . . . . . . . . . 30
3 Mesoscopic spin ratchets 37
3.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37
3.1.1 Ratchets: An overview . . . . . . . . . . . . . . . . . . . . . . . 37
3.1.2 Spin ratchets: General idea . . . . . . . . . . . . . . . . . . . . 39
3.1.3 Coherent spin ratchets based on wire structures realized in 2DEGs 40
3.1.4 Self-consistent calculation of the voltage drop in wire geometries 43
3.1.5 Complementary methods for the creation of pure spin currents . 44ii Contents
3.2 Resonant tunneling-based spin ratchets . . . . . . . . . . . . . . . . . . 45
3.2.1 Mechanism . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 45
3.2.2 Double-dot geometry realized in a 2DEG . . . . . . . . . . . . . 46
3.2.3 Numerical results . . . . . . . . . . . . . . . . . . . . . . . . . . 49
3.3 Spin ratchets based on spin-orbit interaction . . . . . . . . . . . . . . . 53
3.3.1 DC-transport in linear response . . . . . . . . . . . . . . . . . . 54
3.3.2 Creation of pure spin currents . . . . . . . . . . . . . . . . . . . 56
4 Current-induced spin accumulation in wire geometries 67
4.1 Spin accumulation in semiconductors . . . . . . . . . . . . . . . . . . . 68
4.2 Current-induced spin accumulation in quantum wires . . . . . . . . . . 70
4.2.1 Rashba spin-orbit interaction . . . . . . . . . . . . . . . . . . . 71
4.2.2 Rashba and Dresselhaus spin-orbit interaction . . . . . . . . . . 74
4.2.3 Suppression of the current-induced spin accumulation in finite-
sized systems . . . . . . . . . . . . . . . . . . . . . . . . . . . . 75
4.3 Extraction of current-induced spins . . . . . . . . . . . . . . . . . . . . 81
4.4 Electrical detection of current-induced spin accumulation . . . . . . . . 85
4.4.1 Detection principle . . . . . . . . . . . . . . . . . . . . . . . . . 85
4.4.2 Detection by a lead with strong Zeeman splitting . . . . . . . . 88
4.4.3 Detection by a spin selective point contact . . . . . . . . . . . . 91
5 Coherent spin transport in disordered wires and the detection of the
ratio α/β 95
5.1 System of choice . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 95
5.2 Quantum effects in the conductance of disordered wires . . . . . . . . . 96
5.2.1 Weak localization and weak antilocalization . . . . . . . . . . . 97
5.2.2 Universal conductance fluctuations . . . . . . . . . . . . . . . . 100
5.3 Suppression of spin relaxation in quantum wires . . . . . . . . . . . . . 102
5.3.1 Narrow quantum wires . . . . . . . . . . . . . . . . . . . . . . . 102
5.3.2 Rashba and Dresselhaus spin-orbit interaction of equal strength 109
5.4 All-electrical detection of the ratio α/β . . . . . . . . . . . . . . . . . . 112
5.4.1 Outline of the detection mechanism . . . . . . . . . . . . . . . . 112Contents iii
5.4.2 Applicability of the detection mechanism . . . . . . . . . . . . . 113
5.4.3 Influence of the cubic Dresselhaus term . . . . . . . . . . . . . . 116
6 Summary and perspectives 121
References 125