Why is d-wave pairing in HTS robust in the presence of impurities?

TL;DR

This paper explains why d-wave pairing in high-temperature superconductors remains stable despite impurities, especially near optimal doping, due to the development of a forward scattering peak that reduces impurity effects.

Contribution

It introduces a theoretical model showing how doping-dependent charge scattering affects impurity robustness of d-wave pairing in layered superconductors.

Findings

D-wave pairing remains robust near optimal doping despite impurities.

The density of states stays finite at the Fermi surface with impurities.

Robustness diminishes at large doping scattering anisotropy.

Abstract

In the recent theory of strong correlations by Kulic and Zeyher it has been shown that by lowering doping concentration a forward peak in the charge scattering channel is developed. Accordingly, near the optimal doping the nonmagnetic scattering is pronounced in the d-channel and its effect on d-wave pairing is reduced. As a consequence, d-wave pairing is robust against defects and impurities, the order parameter keeps its d-wave shape for any scattering rate and the density of states becomes finite at the Fermi surface. For large doping scattering anisotropy parameter is small and d-wave loses its robustness. The theory is generally formulated for the bi-layer model by including: 1) intra- and inter-plane pairing; 2) intra- and inter-plane impurities.