Impact of disorder on unconventional superconductors with competing ground states

TL;DR

This paper explores how disorder influences competing superconducting states in unconventional superconductors, revealing that impurities can induce or suppress certain pairing symmetries, which is crucial for understanding high-temperature superconductivity.

Contribution

It demonstrates how disorder affects the competition between different pairing states and symmetry-breaking phases using a self-consistent T-matrix approach.

Findings

Disorder induces an s-wave component in d-wave superconductors with subdominant attraction.

Disorder suppresses additional d_{xy} components in the superconducting gap.

Impurities restore translation symmetry in lattice symmetry-breaking phases.

Abstract

Non-magnetic impurities are known as strong pair breakers in superconductors with pure d-wave pairing symmetry. Here we discuss d-wave states under the combined influence of impurities and competing instabilities, such as pairing in a secondary channel as well as lattice symmetry breaking. Using the self-consistent T-matrix formalism, we show that disorder can strongly modify the competition between different pairing states. For a d-wave superconductor in the presence of a subdominant local attraction, Anderson's theorem implies that disorder always generates an s-wave component in the gap at sufficiently low temperature, even if a pure d_{x^2-y^2} order parameter characterizes the clean system. In contrast, disorder is always detrimental to an additional d_{xy} component. This qualitative difference suggests that disorder can be used to discriminate among different mixed-gap structures in high-temperature superconductors. We also investigate superconducting phases with lattice symmetry breaking in the form of bond order, and show that the addition of impurities quickly leads to the restoration of translation invariance. Our results highlight the importance of controlling disorder for the observation of competing order parameters in cuprates.