Physics (Internal)

Examining the Interaction Between Phonons and Dirac Fermion Quasiparticles on the Surface of the Topological Insulator Bi2Se3 via Helium Atom Scattering

This event is part of the Preliminary Oral Exam.

Examining Committee: Michael El-Batanouny, Claudio Chamon, William Skocpol, Robert Carey Abstract: In physics we commonly understand ordered phases of matter using Landau’s approach in which we identify the symmetries that a particular phase breaks.  For example, crystals break continuous translational symmetry as well as certain types of rotational symmetry in real space. Similarly, the field produced by a ferromagnet further reduces crystal symmetry and also breaks time reversal invariance. However, beginning in the early 1980s with the discovery of the integer quantum Hall effect, a new type of order rooted in topology rather than symmetry began to emerge. Continuing on this fruitful path, within the past five years physicists have demonstrated that insulators with time reversal invariant (TRI) Hamiltonians can be classified into two distinct topological groups according to their topological quantum number, Z₂. Those with even Z₂ are trivial insulators while those with odd Z₂ are said to be topological. Unlike the trivial case, topological insulators have robust, gapless, helical <span underline;">surface states protected from backscattering by time reversal invariance. As such, there is excitement about their potential applicability in the fields of spintronics and quantum computing. In this talk I will provide a brief introduction to the concept of topological order and explain how we use helium atom surface scattering to explore the interaction between these exotic electronic states and phonons on the surface of the topological insulator bismuth selenide.