Response, relaxation and transport in unconventional superconductors

TL;DR

This paper studies how impurities and collisions affect the electronic response and ultrasound attenuation in d-wave superconductors, revealing a connection between Raman scattering and shear viscosity, with analytic low-temperature solutions.

Contribution

It introduces a unified t-matrix approach to describe impurity effects on response and transport in unconventional superconductors, linking Raman scattering and viscosity.

Findings

Collision effects dominate quasiparticle relaxation dynamics.

Transport parameters show non-power-law temperature dependence at low T.

Raman response components relate closely to shear viscosity tensor.

Abstract

We investigate the collision-limited electronic Raman response and the attenuation of ultrasound in spin-singlet d-wave superconductors at low temperatures. The dominating elastic collisions are treated within a t-matrix approximation, which combines the description of weak (Born) and strong (unitary) impurity scattering. In the long wavelength limit a two-fluid description of both response and transport emerges. Collisions are here seen to exclusively dominate the relaxational dynamics of the (Bogoliubov) quasiparticle system and the analysis allows for a clear connection of response and transport phenomena. When applied to quasi-2-d superconductors like the cuprates, it turns out that the transport parameter associated with the Raman scattering intensity for B1g and B2g photon polarization is closely related to the corresponding components of the shear viscosity tensor, which dominates the attenuation of ultrasound. At low temperatures we present analytic solutions of the transport equations, resulting in a non-power-law behavior of the transport parameters on temperature.