Unconventional phase transitions in topological insulators and superconductors

Dr. Flavio Nogueira (Hosted by Nussinov), Free University of Berlin

When the effect of interactions is accounted for, topological states of matter can exhibit phase transitions driven by mechanisms that do not comply with the usual Landau-like behavior. For instance, time-reversal symmetry can be spontaneously broken on the surface of topological insulators with in-plane magnetization induced by proximity effect. In this case an out-of-plane component of the magnetization is spontaneously generated, which gaps the Dirac fermion surface states. More interestingly, in some circumstances the conformal symmetry can be spontaneously broken by varying the Hall conductivity in a Chern-Simons quantum electrodynamics description of  a strongly interacting topological insulator. This leads at the same time to a spontaneous breaking of the chiral symmetry. We will show that a conformal phase transition also occurs in a Chern-Simons Higgs description of a topological superconductor. These examples provide a realization of a so called conformality lost, which corresponds to a phase transition scenario discussed before in other contexts.