Spectromicroscopic measurement of surface and bulk band structure interplay in a disordered topological insulator

The authors develop a high-spatial-resolution photoemission technique to show variation of the energy of the Dirac point of approximately 50 meV. They also find an interplay between bulk and surface states. Topological insulators are bulk semiconductors that manifest in-gap surface states with massless Dirac-like dispersion due to the topological bulk-boundary correspondence principle(1-3). These surface states can be manipulated by the interface environment to display various emergent phenomena(4-11). Here, we use angle-resolved photoemission spectroscopy and scanning tunnelling microscopy to investigate the interplay of crystallographic inhomogeneity with the topologically ordered band structure in a model topological insulator. We develop quantitative analysis methods to obtain spectroscopic information, in spite of a limited dwell time on each measured point. We find that the band energies vary on the scale of 50 meV across the sample surface, and this enables single sample measurements that are analogous to a multi-sample doping series. By focusing separately on the bulk and surface electrons we reveal a hybridization-like interplay between fluctuations in the surface and bulk state energetics.