The role of disorder symmetry in a dirty superconductor: a Bogoliubov-deGennes (BdG) study

TL;DR

This study investigates how different types of disorder affect superconductivity in a 2D s-wave superconductor, revealing that off-diagonal disorder more effectively disrupts superconducting order than diagonal disorder.

Contribution

It provides a detailed numerical analysis of the impact of diagonal and off-diagonal disorder on superconductivity using Bogoliubov-deGennes mean-field theory.

Findings

Off-diagonal disorder destroys superconductivity more efficiently.

Diagonal disorder creates isolated superconducting islands.

Large disorder can suppress superconducting order despite connected regions.

Abstract

We study the effect of disorder symmetry in a disordered s-wave superconductor. We begin with an attractive Hubbard model on a two-dimensional square lattice in the presence of diagonal- and off-diagonal disorder. The model is studied numerically using Bogoliubov-deGennes mean-field approach. We find that the off-diagonal disorder is much more efficient in destroying superconducting order. A detailed analysis brings out very distinct qualitative pictures in the two cases: diagonal disorder leads to formation of small scale isolated superconducting islands separated by large region of normal metal, whereas off-diagonal disorder leads to a connected network of superconducting region. Naively, it seems that the connected network of superconducting regions should have a large average value for superconducting order parameter, but this does not hold true for large disorder, as we demonstrate explicitly. Our qualititive picture is supported by real-space data on local order parameters.