Reduced pair breaking from extended disorder in unconventional superconductors: implications to 4Hb-TaS$_2$

TL;DR

This study shows that extended disorder potentials in unconventional superconductors reduce pair-breaking effects, explaining the robustness of unconventional pairing in materials like 4Hb-TaS$_2$ despite high resistivity.

Contribution

The paper introduces a model with extended impurity potentials that significantly diminishes pair-breaking, challenging the conventional Abrikosov-Gor'kov theory predictions.

Findings

Extended impurity potentials reduce pair-breaking rates compared to transport scattering rates.

The reduction in pair-breaking is due to the momentum structure of the disorder potential.

Unconventional pairing states are more robust than previously thought in disordered systems.

Abstract

Unconventional superconductivity is generally expected to be strongly suppressed by nonmagnetic disorder, as captured by Abrikosov--Gor'kov (AG) theory. However, several materials, including transition metal dichalcogenides, exhibit signatures of unconventional pairing despite relatively high resistivities, suggesting a breakdown of the conventional relation between momentum relaxation and pair breaking. Here, we study this problem in H-phase transition metal dichalcogenides by computing the disorder-dressed pairing susceptibility. We employ a multiband model with spin-orbit coupling and include an impurity potential that mimics a common lattice defect, namely a chalcogen vacancy or site ad-atom. This yields to an extended impurity potential, which we compare with the commonly considered on-site (point defect) potential. We evaluate the momentum-relaxation rate and the pair-breaking rate on equal footing. We find that extended impurity potentials lead to a parametrically reduced pair-breaking rate compared to the transport scattering rate, with $\Gamma \tau_D \sim 1/3$ over a wide parameter range. This reduction originates from the momentum structure of the disorder potential, which partially matches the internal structure of the superconducting gap and suppresses pair-breaking processes. As a result, unconventional pairing states are significantly more robust than predicted by standard AG theory. Our results provide a natural explanation for the persistence of unconventional superconductivity in systems with strong disorder and substantially alleviate the apparent conflict between high resistivity and unconventional pairing in materials such as 4Hb-TaS$_2$.