Pair breaking versus symmetry breaking: Origin of the Raman modes in superconducting cuprates
We performed Raman experiments on superconducting Bi2Sr2(Ca1−xYx)Cu2O8+� (Bi-2212) and YBa2Cu3O6+x (Y-123) single crystals. These results in combination with earlier ones enable us to analyze systematically the spectral features in the doping range 0.07 ≤ p ≤ 0.23. In B2g (xy) symmetry we find universal spectra and the maximal gap energy �0 to follow the superconducting transition temperature Tc. The B1g (x 2 −y 2 ) spectra in Bi-2212 show an anomalous increase of the intensity towards overdoping, indicating that the corresponding energy scale is neither related to the pairing energy nor to the pseudogap, but possibly stems from a symmetry breaking transition