title: Optical Conductivity of Topological Surface States with Emergent Supersymmetry.
abstract: Topological states of electrons present new avenues to explore the rich phenomenology of correlated quantum matter. Topological insulators (TIs) in particular offer an experimental setting to study novel quantum critical points (QCPs) of massless Dirac fermions, which exist on the sample's surface. Here, we obtain exact results for the zero- and finite-temperature optical conductivity at the semimetal-superconductor QCP for these topological surface states. This strongly interacting QCP is described by a scale invariant theory with emergent supersymmetry, which is a unique symmetry mixing bosons and fermions. We show that supersymmetry implies exact relations between the optical conductivity and two otherwise unrelated properties: the shear viscosity and the entanglement entropy. We discuss experimental considerations for the observation of these signatures in TIs.
authors.affiliation: Department of Physics, Harvard University, Cambridge, Massachusetts 02138, USA.
authors.forename: William
authors.initials: W
authors.lastname: Witczak-Krempa
authors.affiliation: Department of Physics, University of Alberta, Edmonton, Alberta T6G 2E1, Canada.|Theoretical Physics Institute, University of Alberta, Edmonton, Alberta T6G 2E1, Canada.|Canadian Institute for Advanced Research, Toronto, Ontario M5G 1Z8, Canada.
authors.forename: Joseph
authors.initials: J
authors.lastname: Maciejko