Resonance Raman study of the phonon spectra in superconducting Bi-2212 and Y-123

We studied the variation of phonon spectra with incident photon energy Ei in two superconducting samples, optimally doped YBCO (Tc=93.6 K) and overdoped Bi-2212 (Tc=82 K). Our results highlight the layered nature of the cuprates. Especially the buffer layers that are thought to be responsible for the doping of the CuO2 planes show complex phonon spectra. In Bi-2212 we find an activation of up to 13 phonon modes for a resonance that allows transitions into the Bi-O layers at 3.8 eV. For Y-123 we find also an activation of phonon modes as well as a huge matrix element when transitions into the chains at around 4.1 eV are possible. We also investigate the variation of the line shape of the O(II)-O(III) mode as a function of incident photon energy.