Reference : Spin texture of two-dimensional topological insulators
Dissertations and theses : Doctoral thesis
Physical, chemical, mathematical & earth Sciences : Physics
Spin texture of two-dimensional topological insulators
Rod, Alexia mailto [University of Luxembourg > Faculty of Science, Technology and Communication (FSTC) > Physics and Materials Science Research Unit > ; Technische Universität Dresden - TUD > Fakultät Mathematik und Naturwissenschaften > Institute of Theoretical Physics]
University of Luxembourg, ​​Luxembourg
Technische Universität Dresden, ​Dresden, ​​Germany
Docteur en Physique and Doctor rerum naturalium
viii, 105
Schmidt, Thomas mailto
Vojta, Matthias
Klauss, Hans-Henning
Giamarchi, Thierry
Recher, Patrik
Wirtz, Ludger mailto
[en] spin texture ; topological insulator ; generic helical edge state ; transport ; InAs/GaSb heterostructure
[en] Since the discovery of two-dimensional topological insulators a decade ago, their one-dimensional edge states have attracted significant attention due to their unique properties. For example due to time-reversal symmetry, they are protected against elastic backscattering and they propagate such that electrons with opposite spins move in opposite directions. In fact, the only necessary symmetry to sustain the edge states is time-reversal symmetry. Moreover in experimental setups, the axial spin symmetry seems to be absent. This absence allows new processes to appear such as inelastic backscattering. However, these consequences were neglected in most theoretical works where the spins are considered to be polarized in the z direction.

The aim of this thesis is to provide a more realistic model taking into account a broken axial spin symmetry. In this scheme, we show that a rotation of the spin quantization axis as a function of momentum always appears. This observation leads us to develop a deeper understanding of the size of the rotation related to the material parameters and material models, using also realistic values. It also leads us to understand the implications in real space in cases where translation invariance is lost and how to quantify the rotation in such systems.

The new processes which arise when the axial spin symmetry is broken have important consequences for transport in real materials. To see this, we consider a Hall bar with a hole in its middle, i.e. an antidot. This enables us to create two tunneling regions in order to probe the effect of this generic model. We also consider the effect of Coulomb interactions around the hole, as they can be important in such geometry. We discover that it is possible to probe directly the absence of axial spin symmetry. As experimental evidence is important to investigate our theoretical findings, we propose spectroscopic means to probe the spin texture.

Finally, we also consider one of the experimentally-known candidate materials, namely InAs/GaSb heterostructures. From the k.p Hamiltonian, it is possible to show that their bandstructure shows some anisotropies. The latter is also reflected in the spin texture of their edge states.
Deutsche Forschungsgemeinschaft - DFG ; Swiss National Science Foundation - SNSF

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