Observation of the nonlinear meissner effect in YBCO thin films: evidence for a D-wave order parameter in the bulk of the cuprate superconductors.


We present experimental evidence for the observation of the nonlinear Meissner effect in high-quality epitaxial yttrium barium copper oxide thin films by measuring their intermodulation distortion at microwave frequencies versus temperature. Most of the films measured show a characteristic increase in nonlinearity at low temperatures as predicted by the… (More)