Disorder induced non-Fermi liquid near a metal-superconductor quantum phase transition

Abstract

We study the flux-driven superconductor-metal transition in ultrasmall cylinders observed experimentally by Liu {\em et.al.}(Science 294, 2332 (2001)). Where $T_c\to 0$, there is a quantum critical point, and a large fluctuation conductivity is observed in the proximate metallic phase over a wide range of $T$ and flux . However, we find that the predicted (Gaussian) fluctuation conductivity in the neighborhood of the quantum critical point is 4 orders of magnitude smaller than observed experimentally. We argue that the breakdown of Anderson's theorem at any non-integer flux leads to a broad fluctuation region reflecting the existence of ``rare regions'' with local superconducting order. We calculate the leading order correction to the conductivity within a simple model of statistically induced Josephson coupled local ordered regions that rationalizes the existing data.