Optical study of low-dimensional materials

Electrons in monolayer graphene are described by massless Dirac electrons, which exhibit unique quantum phenomena due to the pseudospin and Berry phase of the massless electrons. In this talk, I will discuss our effort in probing massive Dirac electrons in gapped bilayer graphene, which can be described by a quantum valley Hall insulator with non-trivial Chern number for individual valleys. A topologically protected 1D conducting channel was predicted to exist at the layer-stacking domain boundary of AB-BA bilayers. We show that near-field infrared imaging provides a versatile tool to visualize the layer stacking domain walls, and demonstrate conducting channels arising from the quantum valley Hall edge states through electrical transport in gapped bilayer graphene.