Effect of gap suppression by superfluid current on the nonlinear microwave response ofd-wave superconductors

Abstract

Recently several works have focused on the intrinsic nonlinear current in passive microwave filters as a tool for identifying d-wave order parameter symmetry in the high Tc cuprates. Evidence has been found for d-wave pairing in YBCO and further work has ensued. Most of the theoretical work has been limited to low temperature because it has not included the effect of the superfluid current on the energy gap. We find that this effect leads to important corrections above T~0.2Tc, while leaving the 1/T low temperature behavior intact. A twofold increase in the nonlinear coefficient at temperatures of order ~0.75 Tc is found, and as T->Tc the nonlinearity comes entirely from the effects of the superfluid current on the gap. Impurity scattering has been included and, in addition, signatures for the case of d+s-wave are presented.