Nonlinear Meissner Effect in CuO Superconductors

TL;DR

This paper discusses how the nonlinear Meissner effect in CuO superconductors can be used to identify the nodal lines of the superconducting gap, providing a method to test the proposed $d_{x^2-y^2}$ pairing symmetry.

Contribution

It introduces a way to locate nodal lines in the superconducting gap by analyzing the field dependence of the supercurrent in CuO superconductors.

Findings

Supercurrent field dependence reveals nodal line positions.

Method can test the $d_{x^2-y^2}$ pairing symmetry.

Nonlinear effects are significant at low temperatures.

Abstract

Recent theories of the NMR in the CuO superconductors are based on a spin-singlet $d_{x^2-y^2}$ order parameter. Since this state has nodal lines on the Fermi surface, nonlinear effects associated with low-energy quasiparticles become important, particularly at low temperatures. We show that the field-dependence of the supercurrent, below the nucleation field for vortices, can be used to locate the positions of the nodal lines of an unconventional gap in momentum space, and hence test the proposed $d_{x^2-y^2}$ state.