Condensed Matter Seminar - Nuh Gedik (Massachustts Institute of Technology) "Ultrafast Probing of Dirac Fermions in Topological Insulators"

The three-dimensional topological insulator (TI) is a new phase of matter that exhibits quantum-Hall-like properties, even in the absence of an external magnetic field.  In this talk, I will discuss recent experiments in which we used ultrafast laser pulses to directly visualize spin texture of topological surface electrons and their coupling to the bulk electrons. We find that an idealized helical spin texture only exists within a small energy window about the Dirac point. Our time resolved measurements indicate that coupling between surface and bulk electrons are mediated by phonons.