From immunity to sudden death: Effects of strong disorder in strongly correlated superconductors

TL;DR

This paper studies how strong disorder affects strongly correlated d-wave superconductors, revealing that high disorder destroys superconductivity by creating insulating patches, especially relevant for understanding impurity effects in cuprates.

Contribution

It demonstrates that strong correlations make superconductivity immune to weak disorder but vulnerable to strong disorder, leading to phase separation into insulating and superconducting regions.

Findings

Superconductivity is robust against weak disorder due to strong correlations.

Strong disorder causes formation of Mott insulating patches.

Superconductivity is destroyed efficiently when disorder matches the bandwidth.

Abstract

We investigate the effect of strong disorder on a system with strong electronic repulsion. In absence of disorder, the system has a d-wave superconducting ground-state with strong non-BCS features due to its proximity to a Mott insulator. We find that, while strong correlations make superconductivity in this system immune to weak disorder, superconductivity is destroyed efficiently when disorder strength is comparable to the effective bandwidth. The suppression of charge motion in regions of strong potential fluctuation leads to formation of Mott insulating patches, which anchor a larger non-superconducting region around them. The system thus breaks into islands of Mott insulating and superconducting regions, with Anderson insulating regions occurring along the boundary of these regions. Thus, electronic correlation and disorder, when both are strong, aid each other in destroying superconductivity, in contrast to their competition at weak disorder. Our results shed light on why Zinc impurities are efficient in destroying superconductivity in cuprates, even though it is robust to weaker impurities.