An experimental hunt for the surface states of a 3D topological insulator

Nicholas P. Butch

Center for Nanophysics and Advanced Materials, Department of Physics

University of Maryland, College Park

Three dimensional topological insulators are bulk insulators with metallic surfaces that have a Dirac-like dispersion and spin chirality. The existence of these states is topologically protected, i.e., they are robust against disorder, and as such they are expected to be good conductors. Experimental signatures of these states have been widely reported, but primarily come from surface measurements.

In stark contrast, the surface states are much more difficult to probe via bulk electrical transport measurements. In reality, the materials that are called topological insulators are metals and the bulk conduction masks that of the surface. At the University of Maryland, we have synthesized single crystals of undoped Bi₂Se₃ with exceptionally low bulk carrier density. We have performed a comprehensive study of Hall effect, Shubnikov de Haas oscillations, and optical reflection and transmission on high bulk mobility samples spanning 3 orders of magnitude in carrier density, searching for the surface states. I will discuss our results and their implications for the further pursuit of exotic physics in these materials.