Spectroscopic signature of surface states and bunching of bulk subbands in topological insulator (Bi$_{0.4}$Sb$_{0.6}$)$_2$Te$_3$ thin films

TL;DR

This study uses spectroscopic techniques to analyze the electronic structure of high-quality (Bi$_{0.4}$Sb$_{0.6}$)$_2$Te$_3$ thin films, revealing surface states and quantized bulk subbands consistent with theoretical calculations.

Contribution

It provides the first detailed spectroscopic characterization of surface and bulk states in (Bi$_{0.4}$Sb$_{0.6}$)$_2$Te$_3$ thin films, confirming theoretical predictions.

Findings

Presence of topological surface states with large Te layer contribution

Quantized dispersive bulk energy levels with reduced bandwidth

Strong peaks in local density of states from surface and bulk states

Abstract

High quality thin films of the topological insulator (Bi$_{0.4}$Sb$_{0.6}$)$_2$Te$_3$ have been deposited on SrTiO$_3$ (111) by molecular beam epitaxy. Their electronic structure was investigated by in situ angle-resolved photoemission spectroscopy and in situ scanning tunneling spectroscopy. The experimental results reveal striking similarities with relativistic ab-initio tight binding calculations. We find that ultrathin slabs of the three-dimensional topological insulator (Bi$_{0.4}$Sb$_{0.6}$)$_2$Te$_3$ display topological surface states, surface states with large weight on the outermost Te atomic layer, and dispersive bulk energy levels that are quantized. We observe that the bandwidth of the bulk levels is strongly reduced. These bunched bulk states as well as the surface states give rise to strong peaks in the local density of states.