Condensed Matter Theory

Abstract:

We study transitions between phases of matter with topological order. By studying these transitions in exactly solvable lattice models we show how universality classes may be identified and critical properties described. As a familiar example to elucidate our results concretely, we describe in detail a transition between a fully gapped achiral 2D p-wave superconductor (p + ip for pseudo-spin up/p - ip for pseudo-spin down) to an s-wave superconductor. We show in particular that this transition is of the 2D transverse field Ising universality class. © IOP Publishing Ltd and Deutsche Physikalische Gesellschaft.

Abstract:

We study transport in Weyl semimetals with N isotropic Weyl nodes in the presence of Coulomb interactions or disorder at temperature T. In the interacting clean limit, we determine the conductivity σ(ω,T) by solving a quantum Boltzmann equation within a "leading log" approximation and find it to be proportional to T, up to logarithmic factors arising from the flow of couplings. In the noninteracting disordered case, we compute the Kubo conductivity and show that it behaves differently for ω << T and ω >> T: in the former regime we recover a previous result, of a finite dc conductivity and a Drude width vanishing as NT(2); in the latter, we find that σ(ω,T) vanishes linearly with ω with a leading term as T → 0 equal to the clean, free-fermion result: σ(0)((N))(ω,T = 0) = Ne(2)/12h|ω|/v(F). We compare our results to transport data on Y(2)Ir(2)O(7) and comment on the possible relevance to recent experiments on Eu(2)Ir(2)O(7).