Tunneling spectroscopy of c-axis Y1-xCaxBa2Cu3O7-δ thin-film superconductors

Scanning tunneling spectroscopy was performed on c-axis Y1-xCaxBa2Cu3O7-delta thin films for x = 0, 0.05, 0.15, and 0.20 at 4.2 K. The measured spectra show main-gap, subgap, and satellite features which scale similarly in energy versus Ca doping, suggesting that they are associated with a single pairing energy. The data are analyzed with a multiband tunneling model which attributes the subgap features to the chain band and the satellite and main-gap features to the plane band for d(x2-y2) + s pairing symmetry. These results suggest that the superconductivity in Y1-xCaxBa2Cu3O7-delta involves multiple bands.