Resonance Raman study of 2Δ-gap like features in superconducting BI-2212 and YBCO

We studied the variation of the 2 Δ -gap like peaks with incident photon energy E i in two superconducting samples, optimally doped YBCO ( T c =93.6 K) and overdoped Bi-2212 ( T c =82 K). Our results highlight the composite nature of the 2 Δ -gap like peaks in the HTS. Below the superconducting T c we see a redistribution of spectral weight and the appearance of the 2 Δ -gap like features. In B 1 g Raman symmetry these features change their shape, peak position, and intensity with increasing E i . For E i ∼3.5 eV we find little redistribution, only a strong new peak at a Raman frequency well above the accepted values of twice Δ max .