Speaker
Description
Robust propagating in-gap modes due to spin-orbit domain walls in graphene
Recent success in making twisted multilayered graphene and transition metal dichalcogenides, exhibiting Moiré patterns and consequent domain structures on the nanoscale, raises questions about possible topological electronic states on domain walls (DWs) in presence of multiple induced couplings. We investigate the possible topological electron modes bound to DWs between several types of gapped domains in graphene with spin-orbit coupling, by using both a spectral flow theorem in the continuum theory and tight-binding lattice models.
Surprisingly, we find that a DW across which Valley-Zeeman spin-orbit coupling changes sign, in presence of any constant Rashba spin-orbit, hosts in-gap modes protected by time-reversal symmetry and the bulkgap, although the bulkgap is topologically trivial. The modes are robust even to lattice backscattering on a sharp DW profile, and are similar to those discovered on electric potential DWs in gated bilayer graphene.
Chiral chains with two valleys and disorder of finite correlation length
In one-dimensional chiral systems, electronic states at energy E = 0 evade localization and show a divergent density of states (DOS). For N coupled chains with zero-correlation-length disorder, this divergence persists only for odd N, while even N yields a vanishing DOS. We model N = 2 chiral chains using a thin spinless graphene nanotube with disordered Semenoff mass and Haldane coupling, introducing disorder with tunable correlation length. Because the two valleys at opposite momenta share correlated disorder, the system departs from analytical results assuming independent disorder channels. Numerical simulations show that the DOS remains suppressed for strongly coupled valleys and exhibits a nontrivial crossover as valleys decouple.