Gapless superconductivity in Raman studies of cation substituted Bi2Sr2CaCu2O8+δ

The electronic Raman scattering (ERS) spectrum of the high-temperature superconductor Bi2Sr2CaCu2O8+delta is studied as a function of cation substitution and oxygen content. In unsubstituted crystals with delta near and above that for the optimal T-c, the ERS spectra show a redistribution of spectral weight below T-c consistent with the opening of a superconducting energy gap at 2 Delta. At low oxygen concentrations and in cation substituted samples with optimal oxygen content, the pair-breaking peak is not observed, displaying instead "gapless" or "pseudogap" spectra. When cation substituted samples are post-annealed in high pressure oxygen, the 2 Delta peak remarkably appears. (C) 1998 Published by Elsevier Science Ltd.