Polarized electronic Raman scattering studies of underdoped and overdoped high-T-c superconductors

We report on polarized Raman scattering from high-T, superconductors in the Bi2Sr2 CaCu2 O8+delta (Bi2212) and HgBa2 CuO4+delta (Hg1201) classes, with an emphasis on the effect of superconductivity on the low frequency electr onic continuum. The Hg-based materials confirm earlier observations from Bi 2212 that the superconducting energy gap 2 Delta peak is not present in und erdoped samples, while its Raman shift is maximum in B-1g symmetry at optim al doping, and decreases dramatically with overdoping. These similarities d espite the different numbers of bands crossing the Fermi surface argues aga inst a multiple-band explanation for the anomalous doping dependence of the gap. We also discuss an anomalous B-1g feature observed at 600 cm(-1) in Y underdoped Bi2212. This "pseudogap-like" feature has several properties wh ich suggest it is of electronic - rather than phononic - origin.