ELECTRODYNAMICS OF ND1.85CE0.15CUO4 - COMPARISON WITH NB AND YBA2CU3O7-DELTA

We have measured the surface impedance of Nd1.85Ce0.15CuO4 (NCCO) thin films and single crystals, YBa2Cu3O7-delta (YBCO) single crystals, an d Nb single crystals. We find that the electrodynamic properties of Nb are in good agreement with s-wave BCS theory. YBCO single crystals sh ow behavior which has been seen only in very high quality materials an d which is clearly not consistent with s-wave BCS theory. Both thin fi lms and single crystals of NCCO have been grown, thoroughly characteri zed, and measured at microwave frequencies. We find an unusual degree of consistency in the results between thin films and crystals of NCCO. We also find a surprisingly good agreement between the temperature de pendence of the surface impedance, and single-gap BCS s-wave calculati ons over the entire temperature range. These results are puzzling in t he light of the fact that NCCO is a cuprate superconductor, and the cr ystals were grown in a manner very similar to those of YBCO. We discus s these results and consider a variety of ideas currently in the liter ature which may explain these striking differences.