THESIS
2022
1 online resource (xi, 54 pages) : illustrations (some color)
Abstract
The discovery of topological insulators with boundary states protected by time-reversal
symmetry opened up a new area of research in condensed matter physics. However, it was
shown that gapped topological phases could also be protected by crystalline point group
symmetries, which are known as topological crystalline insulators (TCIs). Antiperovskite
Sr
3PbO was identified as a TCI candidate with nontrivial surface states protected by
mirror symmetry. Using the first-principles calculations and different numerical methods
based on the tight-binding approach, we reveal their topological electronic structure in
their bulk and thin-film systems. We prove that the odd-atomic-layer thin film with
Sr
2-O terminated surfaces is the stablest 2D phase. Moreover, we show the topological
phase transi...[
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The discovery of topological insulators with boundary states protected by time-reversal
symmetry opened up a new area of research in condensed matter physics. However, it was
shown that gapped topological phases could also be protected by crystalline point group
symmetries, which are known as topological crystalline insulators (TCIs). Antiperovskite
Sr
3PbO was identified as a TCI candidate with nontrivial surface states protected by
mirror symmetry. Using the first-principles calculations and different numerical methods
based on the tight-binding approach, we reveal their topological electronic structure in
their bulk and thin-film systems. We prove that the odd-atomic-layer thin film with
Sr
2-O terminated surfaces is the stablest 2D phase. Moreover, we show the topological
phase transition between quantum spin Hall and the normal insulating phase occurred
as we increase the thickness of the thin film. This behavior can also be obtained using a
low-energy effective model with infinite potential well boundary conditions. The notion
of topology can be generalized to the gapless system. We study a nitride anti-perovskite
class material with a non-collinear AFM structure. It hosts a number of Weyl-point
pairs around the Fermi level, which contribute a large amount of Berry curvature. The
magnetization of the unit-cell increase with the strength of the applied strain. This is
the source of a large anomalous Nernst signal observed in the experiment. We provid
numerical evidence for this phenomenon.
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