Raising the critical temperature by disorder in unconventional superconductors mediated by spin fluctuations

TL;DR

This paper introduces a theory showing that disorder can unexpectedly increase the critical temperature in unconventional superconductors by affecting spin fluctuations, challenging traditional views on impurity effects.

Contribution

It presents a self-consistent real space model demonstrating how disorder can enhance Tc through spin fluctuation modulation in unconventional superconductors.

Findings

Disorder can weaken Tc suppression compared to Abrikosov-Gor'kov theory.

Impurities can locally enhance pairing by softening spin fluctuations.

Disorder may lead to Tc enhancements depending on impurity potential and magnetic proximity.

Abstract

We propose a mechanism whereby disorder can enhance the transition temperature Tc of an unconventional superconductor with pairing driven by exchange of spin fluctuations. The theory is based on a self-consistent real space treatment of pairing in the disordered one-band Hubbard model. It has been demonstrated before that impurities can enhance pairing by softening the spin fluctuations locally; here, we consider the competing effect of pair-breaking by the screened Coulomb potential also present. We show that, depending on the impurity potential strength and proximity to magnetic order, this mechanism results in a weakening of the disorder-dependent Tc-suppression rate expected from Abrikosov-Gor'kov theory, or even in disorder-generated Tc enhancements.