Thermoelectric Imaging of Domain Boundary States in Epitaxial Graphene

We investigated electronic states associated with the boundary structure between domains of two carbon layers in epitaxial graphene. The topological structure formed between AB and BA stacking domains could be observed in microscopic thermoelectric measurements down to the atomic length scale. Measurements show that the boundary structure observed from epitaxial bilayer graphene is associated with point defects of carbon pentagon-heptagon and the structure forms a closed loop. Such structural patterns define soliton-like domain walls driven by strain in epitaxial graphene, which gives rise to prominent contrast in the thermoelectric measurement. The contrast observed over the domain walls in the measurement of thermoelectric response is the direct consequence of chiral boundary modes expected for tensile-strained boundaries, which is similar to the structures observed in exfoliated and CVD-grown bilayer graphene. These results will help to elucidate how the topological band plays in epitaxial graphene.