Quantum valley Hall states in low-buckled counterparts of graphene bilayer
Abstract
With low-buckled structure for each layer in graphene bilayer system, there breaks inversion symmetry (P-symmetry) for one stacking when both A and B sublattices in top layer are aligned with those in bottom layer. In consideration of spin-orbit coupling (SOC), there opens nontrivial topological gap in each monolayer system to achieve quantum spin Hall effect (QSHE). As long as time-reversal symmetry (T-symmetry) is preserved the gapless edge states is robust in each individual layer even for the bilayer absent of PT symmetry. Based on this platform and through tight-binding (TB) model calculations we find it becomes a typical system that can exhibit quantum valley Hall effect (QVHE) when introduced a layer-resolved Rashba SOC that leads to band inversion at each K valley in the hexagonal Brillion zone (BZ). The topological transition comes from that the valley Chern number Cv = CK - CK' switches from 0 to 2, which characterizes the nontrivial QVHE phase transited from two coupled Z2 topological insulators. We also point that the layer-resolved Rashba SOC can be introduced equivalently by twisting two van der Waals touched layers. And through TB calculations, it is shown that the K bands inverts in its corresponding mini BZ when the two layers twisted by a small angle. Our findings advance potential applications for the devices design in topological valleytronics and twistronics.
- Publication:
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arXiv e-prints
- Pub Date:
- March 2024
- DOI:
- 10.48550/arXiv.2403.13277
- arXiv:
- arXiv:2403.13277
- Bibcode:
- 2024arXiv240313277S
- Keywords:
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- Condensed Matter - Mesoscale and Nanoscale Physics;
- Condensed Matter - Materials Science