1:30 pm VIA ZOOM
Topology and broken symmetry of excitons in two-dimensional materials, Sid Parameswaran, Oxford
I will discuss recent theoretical work on exciton physics in two-dimensional materials. First, I will focus on the neutral particle-hole pair excitations of correlated “orbital Chern insulators” recently detected in twisted bilayer graphene, whose approximately flat conduction and valence bands have equal and opposite non-zero Chern number. Using a mix of exactly solvable models and microscopic nuumerical simulations, I will argue that these features can combine to endow the exciton bands with nontrivial Berry curvature . I will then argue, more speculatively, that under certain circumstances this sould stabilize a series of “excitonic” fractional quantum Hall states descending from the parent “integer" OCI state . I will then change gears to describe recent experiments on monolayer WTe2. I willl describe the zero-field excitonic insulating phase thought to be present in this system, and clarify the role played by band topology in the competition between distinct broken-symmetry exciton orders . I will also comment on the concomitant observation of quantum oscillations coincident with insulating behaviour when the same system is placed in a transverse magnetic field.