The Condensed Matter & Surface Sciences Colloquium Series presents David Lederman of West Virginia University on “Probing the Surface States of Topological Insulators,” on Thursday, Feb. 11, at 4:10 p.m. in Walter 245.
David Lederman
Abstract: There has been much recent interest in a new class of materials called three-dimensional topological insulators, where the bulk of the material is insulating and surface states are metallic. Backscattering from non-magnetic defects is theoretically forbidden for these surface states due to quantum interference originating from locking between the spin and momentum degrees of freedom. While the existence of the surface states has been shown to exist using photoemission experiments, measuring the transport properties of these states is much more difficult. For example, 3D topological insulator materials, such as Bi2Se3 and Bi2Te3, normally have defect states in the bulk that contribute to the overall conductivity. In addition to producing samples with better structural quality, it is necessary to decrease the sample thickness to accentuate the effects of the surfaces states. However, the bulk of these thin films behave as two-dimensional conductors with strong spin-orbit coupling, and the electrical transport properties at low temperatures resulting from weak anti-localization resemble those of the surface states. I will discuss recent efforts by my group to query the surface states directly using optical techniques, including ultrafast and non-linear optical measurements and Raman scattering. I will demonstrate that all-optical methods for measuring the properties of the surface states is a promising avenue for revealing the dynamic properties of the surface states.
This work was supported by a West Virginia Higher Education Policy Commission Research Challenge Grant.
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