Resonance properties in optimally and overdoped Y-123 - investigation of phonons and the electronic background

We have studied the variation of the 2$\Delta$-gap like features and the phonons in optimally to overdoped Y-123 with incident photon energy E$_{i}$. The optimally doped YBCO and overdoped YBCO exhibit a complex behavior in the gap feature when the incident photon energy is tuned from 1.8 eV to above 5 eV. Our results highlight the composite nature of the 2$\Delta$-gap like peaks in the HTS. Below the superconducting T$_{c}$ we see a modification of spectral weight and the appearance of the 2$\Delta$ like features. In B$_{1g}$ Raman symmetry these features change their shape, peak position, and intensity with increasing E$_{i}$. For E$_{i}$ 3.5 to 4 eV we find little redistribution, only a strong new peak at Raman frequencies well above the accepted values of twice $\Delta _{max}$. This peak is located at 620 cm$^{-1}$ in optimally doped samples, it shifts to lower energies and broadens in overdoped materials. The matrix element of this peak shifts as a function of doping by 0.2 eV to higher incident photon energies, outlining the interplay between the local electronic structure and superconductivity. Strong resonances of the chain disorder-induced phonons appear at around 4.1 eV, which are absent in the overdoped material.