%0 Journal Article
%T Landau level spectroscopy of surface states in the topological insulator Bi$_{0.91}$Sb$_{0.09}$ via magneto-optics
%A A. A. Schafgans
%A A. A. Taskin
%A Yoichi Ando
%A Xiao-Liang Qi
%A B. C. Chapler
%A K. W. Post
%A D. N. Basov
%J Physics
%D 2012
%I arXiv
%R 10.1103/PhysRevB.85.239903
%X 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.
%U http://arxiv.org/abs/1202.4029v1