In-plane optical spectra of Y1-xCaxBa2Cu3O7-δ: Overdoping and disorder effects on residual conductivity

We measured the temperature dependence of the in-plane polarized reflectivity spectra of twin-free Y1-xCaxBa2Cu3O7-delta single crystals with different Ca concentrations (x = 0, 0.11, and 0.16) from the optimally doped to heavily overdoped region. Low-energy optical conductivity spectra showed a Drude-like residual conductivity at temperatures far below the superconducting transition temperature, which indicates the presence of unpaired-normal carriers in the superconducting state. Comparing the spectra at a fixed Ca content or at a fixed doping level, we have revealed that the carrier overdoping increases unpaired carriers in addition to those induced by the Ca disorder. We also found the superconducting behavior of the one-dimensional CuO chains for the Ca-free samples.