Spin-reserved quantum spin Hall effects are robust two-dimensional topological phases characterized by spin Chern numbers. Like Chern insulators, quantum spin Hall effects allow for multiple pairs of edge states, electron fractionalization, and time-reversal symmetry breaking. In this talk, I will discuss our recent observations of both integer and fractional quantum spin Hall effects in two moiré materials: twisted WSe2 and twisted MoTe2. In weakly interacting twisted WSe2, only integer quantum spin Hall effects are observed at even integer moiré lattice fillings. In strongly interacting 2.1-degree twisted MoTe2, both integer quantum spin Hall effects at even fillings and a fractional quantum spin Hall effect at an odd filling factor of 3 are observed. In addition, I will also discuss the fractional Chern insulators and higher (2nd and 3rd) moiré band magnetism in small-angle twisted MoTe2 devices.
 

Biosketch

Kaifei Kang is a Postdoc in the Kin Fai Mak and Jie Shan group at Cornell University, where his research focuses on investigating topological, correlated, ferroelectric, and superconducting phenomena in 2D material heterostructures. Kaifei earned his PhD in the same group in 2022.

Please contact phweb@ust.hk should you have questions about the talk.