ISBN 9783843945301

978-3-8439-4530-1, Reihe Physik

Petra Högl
Spin-orbit coupling effects in tunnel junctions and graphene

153 Seiten, Dissertation Universität Regensburg (2019), Softcover, A5

Zusammenfassung / Abstract

Spintronics aims to create new concepts for data processing and storage by exploiting the spin degree of freedom of electrons. A key interaction for this is spin-orbit coupling (SOC). We focus on interfacial spin-orbit fields which are behind a wealth of new phenomena, such as the tunneling anisotropic magnetoresistance effect (TAMR) or interfacial spin-orbit torques. Recent advances have revealed even broader implications of SOC, e.g., in the design of topological systems such as topological insulators, skyrmions, and Majorana fermions. By now the field of topological states of matter has become one of the main research areas of condensed matter physics due to its fascinating physics and potential applications in electronics, spintronics, and quantum computation. We study graphene as a promising platform for topological phases due to its outstanding electronic properties which can be modified by proximity effects.

In the first part of this thesis, we theoretically investigate SOC effects in ferromagnet/superconductor junctions. We find a magnetoanisotropy, which we term magnetoanisotropic Andreev reflection (MAAR), with a giant magnitude compared to the TAMR, its normal-state analog. We trace this back to the strong influence of interfacial spin-orbit fields on Andreev reflection and conclude that merging the concepts of spintronics with superconductivity could enhance functionality and performance of devices.

In the second part, we use realistic tight-binding models to explore topological phases in graphene modified by proximity effects. Graphene on transition-metal dichalcogenides shows a staggered functional form of the intrinsic SOC. By considering these newly unveiled staggered regimes for spin-orbit and exchange couplings we find quantum anomalous Hall effect (QAHE) phases and propose a material platform for such systems. Adding proximity-induced superconductivity turns the QAHE systems into topological superconductors exhibiting chiral Majorana states.