O Abstract : 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.