Landau level spectroscopy of surface states in the topological insulator Bi$_{0.91}$Sb$_{0.09}$ via magneto-optics

TL;DR

This study uses magneto-infrared spectroscopy to analyze Landau levels in the topological insulator Bi$_{0.91}$Sb$_{0.09}$, revealing insights into its surface and bulk electronic properties.

Contribution

It provides the first broad-band magneto-optical measurements of Landau levels in this specific topological insulator, linking optical transitions to electronic structure.

Findings

Measured the direct band gap between conduction and valence bands.

Observed Landau level transitions with frequency scaling as √H.

Discussed implications for surface and bulk states in topological insulators.

Abstract

We have performed broad-band zero-field and magneto-infrared spectroscopy of the three dimensional topological insulator Bi$_{0.91}$Sb$_{0.09}$. The zero-field results allow us to measure the value of the direct band gap between the conducting $L_a$ and valence $L_s$ bands. Under applied field in the Faraday geometry (\emph{k} $||$ \emph{H} $||$ C1), we measured the presence of a multitude of Landau level (LL) transitions, all with frequency dependence $\omega \propto \sqrt{H}$. We discuss the ramification of this observation for the surface and bulk properties of topological insulators.