I discuss the interplay between non-Fermi liquid behaviour and superconductivity near a quantum-critical point (QCP) in a metal. It is widely thought that the tendency towards superconductivity and towards non-Fermi liquid behaviour compete with each other, and if the pairing interaction is reduced below a certain threshold, the system displays a naked non-Fermi liquid QC behaviour. I show that the situation is more complex as there are multiple solutions for Tc at a QCP. For all solutions, except one, Tc vanishes when the pairing interaction drops below the threshold. However, there exists one solution, for which Tc remains finite even when the pairing interaction is arbitrary small, despite that there is no Cooper logarithm. I argue that superconductivity between this Tc and a lower T, when other solutions appear, is special, as it is confined to fermions with the first Matsubara frequency. I discuss the implications for the density of states and the spectral function. I argue that there are two qualitatively different regimes of system behaviour below the onset of pairing – at low T the pairing gap closes with increasing T, at higher T, it gets filled in, but remains finite.
Andrey Chubukov / University of Minnesota
Event Details & Abstracts