One of the most exciting developments in condensed matter physics over the last thirty years has been the discovery of topological phases of matter. Under the broadest possible definition, a system is in a topological phase if there is a gap in its bulk spectrum. Of course, such a definition describes any ordinary thermal or electrical insulator. The key theoretical breakthrough was the realization that not all insulators are created equal. In fact, given a model for an insulating system, there exist certain numerical invariants - topological quantum numbers - that we can compute in order to distinguish between different possible topological phases. These invariants vanish for most ordinary insulators (strictly speaking, they take the same values as in the vacuum) - they are "topologically trivial". The distinguishing feature of such topological invariants is that they depend on the global structure of the system under consideration; topological phases are not locally ordered like magnets or solids. Consequently, systems in nontrivial topological phases are host to a wide range of exotic phenomena, from quantized transport coefficients to fractional bulk excitations that harbor the potential to allow for fault tolerant quantum computation.
Since this initial discovery, the influence of topology has spread across all areas of condensed matter physics. It is this--in addition to individual realizations of topological phases--that is in my opinion the biggest boon of this new paradigm. Topology now stands alongside abstract algebra (as it pertains, for instance, to symmetry groups) as one of our main tools for exploring quantum phenomena in solids and liquids. Broadly speaking, the goal of my research is to marry ideas from these two areas in order to study new phenomena in condensed matter. Currently, I am focusing on the following main topics:
1. Viscous and optical response of topological insulators and semimetals
2. Magnetic topological materials
3. Crystal symmetry protected topological phenomena