A tunneling spectroscopy study of the pairing symmetry in the electron-doped Pr1−xLaCexCuO4−y

We have performed scanning tunneling spectroscopy and point contact spectroscopy measurements on the electron-doped superconductor Pr1−xLaCexCuO4−y (x = 0.12, Tc ? 25 K). We address the question of the symmetry of the order parameter and of the amplitude of the energy gap. We compare three possible scenarios, i.e. isotropic s-wave,‘anisotropic’ s-wave, and d-wave. Evidence for a d-wave symmetry of the order parameter is given. From the temperature evolution of the dI/dV versus V characteristics we extract a BCS-like temperature dependence of the superconducting energy gap ?. Despite the variety of measured spectra we give a consistent explanation for the whole set of data, indicating ? = (3.6 ± 0.2) meV and a ratio 2?/KBTC ? 3.5 ± 0.2. In particular, point contact characteristics showing gap-like features at higher voltages have been interpreted by considering the formation of an intergrain Josephson junction in series with the point contact junction. Further confirm...