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, T-c similar or equal to 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 Delta. Despite the variety of measured spectra we give a consistent explanation for the whole set of data, indicating Delta = (3.6 +/- 0.2) meV and a ratio 2 Delta / KBTC similar or equal to 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 confirmation of the correctness of the model is given by the behavior of the critical current of the intergrain Josephson junction versus temperature which follows the Ambegaokar-Baratoff behavior.