Tunable electron topology and correlation in few-layer rhombohedral graphene 

Graphene has been a model solid state system where novel quantum phenomena emerge from the interplay between symmetry, band topology and reduced dimensionality. In particular, few layer graphene with the rhombohedral stacking order has a unique bandstructure with an electrically tunable bandgap and a valley-dependent Berry phase. These features result in unusual electrical and optical properties, for which optical spectroscopy/microscopy are powerful characterization tools. In this talk, I will first show our experimental demonstration of the topological valley transport at AB/BA stacking domain walls in bilayer graphene. These domain walls are 1D conducting channels that feature the quantum valley Hall edge states. Next, I will present our efforts on probing the orbital magnetism of electrons through studying excitons in bandgap-tuned bilayer graphene. Due to the electron pseudospin and Berry curvature effects, these excitons obey unusual valley-dependent optical selection rules and a large valley g-factor of 20 in magnetic field. Finally, I will show our recent work on probing strong electron correlation in ABC trilayer graphene and its implications for correlation-driven topological phenomena.

References:
J Yang et al., "Spectroscopy signatures of electron correlations in a trilayer graphene/hBN moiré superlattice", Science, 375, 1295 (2022)
L. Ju et al., "Tunable excitons in bilayer graphene", Science, 358, 907 (2017)
L. Ju et al., "Topological valley transport at bilayer graphene domain walls", Nature , 520, 650 (2015)