Nonlinear Current Response of a d-wave Superfluid

TL;DR

This paper reexamines the nonlinear electromagnetic response of d-wave superconductors, highlighting the stability of certain nonlinear effects and discussing experimental challenges in observing these phenomena.

Contribution

It provides a detailed analysis of the nonlinear response in d-wave superconductors, emphasizing the robustness of the quadratic field dependence over the linear one.

Findings

Nonlinear coefficient shows an upturn with quadratic field dependence.

Linear response is limited by the lower critical field and nonlocal effects.

Impurities influence the nonlinear response and complicate observations.

Abstract

Despite several efforts the nonlinear Meissner effect in d-wave superconductors, as has been discussed by Yip and Sauls in 1992, has not been verified experimentally in high-Tc superconductors at present. Here, we reinvestigate the nonlinear response expected in a d-wave superconductor. While the linear H field dependence of the penetration depth, predicted by Yip and Sauls, is restricted by the lower critical field and can be masked by nonlocal effects, we argue that the upturn of the nonlinear coefficient of the quadratic field dependence is more stable and remains observable over a broader range of parameters. We investigate this by studying the influence of nonmagnetic impurities on the nonlinear response. We discuss the difficulties of observing this intrinsic d-wave signature in present day high-Tc films and single crystals.