Raman spectroscopy in YBa2Cu3O6+x and Bi2Sr2(CaxY1-x)Cu2O8+delta: Pseudogap and superconducting gap

We present results of Raman-scattering experiments in differently doped YBa 2Cu3O6+x (Y-123) and Bi2Sr2(CaxY1-x)CU2O8+delta (Bi-2212) single crystals. When reducing the doping level x the scattering intensity in B-1g, symmetry increases while it decreases in the Bz, channel. This anisotropic behavior can be attributed to a qualitative change of the Fermi surface topology. A t B-2g symmetry we find evidence of a pseudogap Delta* in the normal state below a characteristic temperature T*approximate to 180 K. In the supercond ucting state, the spectra obtained from overdoped samples show the well-kno wn pair-breaking (2 Delta) features in both B-1g and B-2g symmetries while in the underdoped regime pair-breaking maxima can only be observed in the B z, channel. The magnitude of the gap can be estimated to be approximately 8 kT(c), and is, from our experiments, different from Delta*.