Transport anomalies in multiband superconductors near quantum critical point

Abstract

We study the effects of quantum fluctuations on the transport properties of multiband superconductors near a pair-breaking quantum critical point. For this purpose, we consider a minimal model of the quantum phase transition in a system with two nested two-dimensional Fermi surfaces. Under the assumption that doping the system adds nonmagnetic impurities but does not change the densities of carriers, we include disorder potentials that render both intra- and interband collisions. Interband scattering leads to full suppression of the unconventional $s^{\pm}$ superconducting order similar to the effect of paramagnetic impurities in isotropic single-band superconductors. We use the diagrammatic technique of quantum field theory to compute the corrections to electrical conductivity in a normal state due to superconducting fluctuations in the entire low-temperature quantum regime. We show that the sign of the conductivity correction depends on how the quantum critical point is approached in the phase diagram. We contrast our findings to existing approaches to this problem based on the renormalization group, time-dependent Ginzburg-Landau phenomenology, and effective bosonic action field theories.