Low-Frequency Optical Conductivity in Inhomogeneous d-wave Superconductors

TL;DR

This paper investigates how spatial inhomogeneity in phase stiffness and normal fluid density in d-wave superconductors leads to low-frequency optical dissipation, explaining experimental observations in cuprate films.

Contribution

It introduces a model linking inhomogeneity in superfluid density to low-frequency dissipation, providing a possible explanation for experimental data.

Findings

Inhomogeneity causes spectral weight transfer from zero to finite frequencies.

Anti-correlation between phase stiffness and normal fluid density enhances dissipation.

Model aligns with optical conductivity measurements in cuprate superconductors.

Abstract

Motivated by the recent optical conductivity experiments on Bi_2Sr_2CaCu_2O_{8+delta} films, we examine the possible origin of low-frequency dissipation in the superconducting state. In the presence of spatial inhomogeneity of the local phase stiffness rho_s, it is shown that some spectral weight is removed from omega=0 to finite frequencies and contribute to dissipation. A case where both rho_s and the local normal fluid density are inhomogeneous is also considered. We find an enhanced dissipation at low frequency if the two variations are anti-correlated.