Electronic Structure of Multilayer Rhombohedral Graphite Studied Using STM

Multilayer rhombohedral graphite is predicted to possess an electronic structure that contains low-energy, dispersionless flat surface bands and a gapped bulk. Here we present a study of the surface states of rhombohedral graphite of various thicknesses using Scanning Tunneling Microscopy/Spectroscopy (STM/STS). In the density of states of all samples we observe a van Hove singularity (vHS) that we attribute to the top surface flat band. This vHS increases in height and decreases in width as sample thickness increases. Peaks that correspond to higher energy band edges are also observed.In our thickest 14-layer device, we study a natural boundary between hexagonal and rhombohedral graphite. These individual graphite stacking orders are believed to be topologically trivial and non-trivial, respectively. Our experimental results reveal a splitting of the van Hove singularity in the local density of states over a distance of 15 nm as the boundary transitions from rhombohedral to hexagonal stacking. Tight-binding calculations reveal that this splitting may be explained through the introduction of gradual stacking faults throughout the boundary.