Disorder Effects on the Intrinsic Nonlinear Current Density in YBa2Cu3O7−δ

We present harmonic generation measurements of the intrinsic nonlinear current density j₂ of YBa₂Cu₃O_7-delta (YBCO) films at temperatures close the T_c. Experiments on a range of different quality samples allow us to extract the dependence of j₂ on the penetration depth of the superconductor. In order to model these results, we calculate the intrinsic nonlinear current response of d_x ² _-y ²-wave superconductors in the Meissner regime in the presence of nonmagnetic impurities within the self-consistent T-matrix approximation.