University of Groningen Taking topological insulators for a spin de Vries, Eric Kornelis IMPORTANT NOTE: You are advised to consult the publisher's version (publisher's PDF) if you wish to cite from it. Please check the document version below. Document Version Publisher's PDF, also known as Version of record Publication date: 2017 Link to publication in University of Groningen/UMCG research database Citation for published version (APA): de Vries, E. K. (2017). Taking topological insulators for a spin: Towards understanding of spin and charge transport in Bi2Se3 [Groningen]: Rijksuniversiteit Groningen Copyright Other than for strictly personal use, it is not permitted to download or to forward/distribute the text or part of it without the consent of the author(s) and/or copyright holder(s), unless the work is under an open content license (like Creative Commons). Take-down policy If you believe that this document breaches copyright please contact us providing details, and we will remove access to the work immediately and investigate your claim. Downloaded from the University of Groningen/UMCG research database (Pure): http://www.rug.nl/research/portal. For technical reasons the number of authors shown on this cover page is limited to 10 maximum. Download date: 29-01-2019
Antonija, papa, mama en Marjon, jullie zijn de beste!
Zernike Institute PhD thesis series 2017-21 ISSN: 1570-1530 ISBN: 978-94-034-0264-2 (hardcopy version) ISBN: 978-94-034-0265-9 (electronic version) The work described in this thesis has been performed in the research group Spintronics of Functional Materials, which is part of the Zernike Institute for Advanced Materials at the University of Groningen, the Netherlands. The research has been supported by the Bonus Incentive Scheme (Dieptestrategie) of the Dutch Ministry for Education, Culture, and Science (OCW). Cover: The cover displays the abstract representation of highway traffic at night where headlights and taillights are the unique feature that describes the direction of movement. In the context of this thesis, the headlights and taillights represent the two distinct spin states of charge carriers. Like the lights in traffic, the spin states in topological insulators immediately relate to the charge carrier s momentum. As the endpoint of the highway is in the dark, so is the one of topological insulators. This thesis contributes to the understanding, but it remains an effort to employ the full potential of topological insulators. The image and its rights were purchased from Shutterstock. Idea by: Eric de Vries. Suggestions were made by Antonija Marjanovic and Jermaine de Beauvesier Watson for which the author is very thankful. Printed by: Gildeprint, Enschede
Taking topological insulators for a spin Towards understanding of spin and charge transport in Bi 2 Se 3 Proefschrift ter verkrijging van de graad van doctor aan de Rijksuniversiteit Groningen op gezag van de rector magnificus prof. dr. E. Sterken en volgens besluit van het College voor Promoties. De openbare verdediging zal plaatsvinden op vrijdag 24 november 2017 om 09.00 uur door Eric Kornelis de Vries geboren op 26 maart 1990 te Delfzijl
Promotores Prof. dr. T. Banerjee Prof. dr. ir. B.J. van Wees Beoordelingscommissie Prof. dr. ir. B.J. Kooi Prof. dr. M.S. Golden Prof. dr. S.O. Valenzuela
Contents Summary Samenvatting V VII 1 Introduction 1 1.1 Topology: Exploring new states of matter 2 1.2 Topological insulators and their high potential 3 1.3 Thesis outline 4 1.4 References 6 2 Properties of topological insulators 7 2.1 Crystal structure 8 2.2 Topological band theory 9 2.3 Bi-based topological insulators 16 2.4 Growth 17 2.4.1 Thin films 18 2.4.2 Bulk crystals, nanoplatelets, and nanoribbons 20 2.5 References 20 3 Studying charge transport at metal/topological insulator interfaces 25 3.1 Introduction 26 3.2 Measurement schemes to study transport at the interface 28 3.2.1 Ballistic-electron emission microscopy 28 3.2.2 Hot-electron transistor 30 3.2.3 Three-terminal measurements 31 3.3 Device fabrication 32 3.3.1 BEEM devices 32 3.3.2 Solid-state device geometries 34 3.4 Results and Discussion 37 3.4.1 BEEM devices 37 3.4.2 Solid-state device geometries 40 3.5 Conclusions 45 3.6 References 46 I
4 Investigation of helicity-dependent photocurrent generation in Bi 2 Se 3 51 4.1 Introduction 52 4.2 Theory 53 4.2.1 Generation of current through optical excitation 53 4.2.2 Transient charge-carrier dynamics in topological insulators 56 4.3 Experimental Methods 57 4.4 Results and Discussion 60 4.4.1 Temperature dependence 60 4.4.2 Position dependence 63 4.5 Conclusions 68 4.6 References 68 5 Charge transport under high magnetic fields in Bi 2 Se 3 73 5.1 Introduction 74 5.2 Lifshitz Kosevich theory 74 5.3 Results and Discussion 77 5.4 Conclusions 83 5.5 Appendix 84 5.5.1 Additional data 84 5.5.2 Derivation of the two-carrier model 93 5.5.3 Details on analysis of oscillations 95 5.5.4 Improvement of the FFT spectra 96 5.5.5 Negative magnetoresistance 98 5.5.6 Weak antilocalization 99 5.6 References 102 6 Investigating charge-current-induced spin voltage signals in Bi 2 Se 3 105 6.1 Introduction 106 6.2 Theory 107 6.2.1 Detection of charge-current-induced spin accumulation in topological insulators 107 6.2.2 Estimation of the charge-current-induced spin polarization 110 6.3 Results and Discussion 112 6.4 Conclusions 118 6.5 Outlook 118 6.6 Appendix 123 6.6.1 Additional Measurements 123 6.6.2 Modeling of current spread 126 6.6.3 Analytical expression for fringe fields 126 6.7 References 128 7 Taking topological insulators for their spin: A feasibility study 131 7.1 Production of topological insulator materials 132 7.1.1 Mining and purification of raw materials 132 7.1.2 Environmental impact 133 7.1.3 Large-area growth 134 II
7.1.4 Conclusions 135 7.2 Applicability of topological insulators 135 7.2.1 Spintronic applications 136 7.2.2 Thermoelectric applications 140 7.2.3 Applications for optics 141 7.3 Conclusions 143 7.4 References 143 Appendix: Details on fabrication 147 Acknowledgments 151 III