Electronic Raman scattering in heavily overdoped (Y,Ca)Ba2Cu3O7-δ crystals

In order to get insight into the overdoped electronic state, Raman scattering in heavily overdoped detwinned (Y,Ca)Ba2Cu3O7-δ crystals (Tc=65 K) has been investigated. In the A1g and B1g polarizations, the electronic pair-breaking peak is located at nearly the same energy of about 220 cm-1, in contrast to the polarization dependent position of the peak in optimally doped YBa2Cu3 O7-δ crystals. The result is in favor of d + s-pairing symmetry in this overdoped material. The spectra also show the strong superconductivity induced XY-anisotropy in intensity of the pair-breaking peak, which indicates the existence of quantum interference between CuO2 planes and CuO-chains in this compound