Speaker
Description
I will review recent work on quantum criticality in three-dimensional gapless semiconductors, which feature quadratic band crossing at the fermi level. These rather ubiquitous systems, such as gray tin and mercury telluride, feature only a Galilean (z=2) invariance at low energies, and should exhibit interesting new phases and transitions as a result of electron-electron and electron-phonon interactions. I will discuss how the phenomenon of fixed point collision replaces the putative Abrikosov's scale-invariant phase with a nematic insulator at low energies, with the former phase leaving a trace in the characteristic separation of scales that ensues. A sufficiently strong electron-phonon interaction, on the other hand, leads to a quantum critical point with emergent particle-hole and rotational symmetries, but also with a non-integer dynamical critical exponent, at which the system develops s-wave superconducting order.
