Superconductivity and localization near a two-dimensional ferromagnetic quantum critical point

We study the influence of disorder on the superconducting transition in a two-dimensional Fermi liquid coupled to the soft Ising-ferromagnetic order-parameter fluctuations associated with proximity to a quantum critical point. We determine the superconducting transition temperature, the temperature dependence of the resistivity, and the phase diagram. The analysis is based on the renormalization group for a modified nonlinear sigma model developed by us in [1]. We demonstrate that diffusion and localization effects drastically modify the interplay between fermionic incoherence and strong pairing interactions leading to a possible strong enhancement of superconductivity, eventually followed by the superconductor-insulator transition.

DOE Office of Basic Energy Sciences, contract DEAC02-76SF00515.