Intergranular critical current behavior of granular superconducting Sm2-xCexCuO4-y compounds

We have measured electrical resistivity versus temperature and current-voltage characteristics isotherms on granular samples of superconducting Sm2-xCexCuO4-y (x = 0.19 and 0.20). The superconductivity in these compounds can be described by a collection of superconducting islands embedded in an insulating matrix, and exhibit a paracoherent-coherent-like transition at temperatures T-cj < 6 K. The temperature dependence of the critical current follows the Josephson-junction critical current predictions remarkably well over the temperature range studied 1.35 < T < 6 K. Such a behavior suggests that the wide distribution of intergranular resistance <Delta>R-in behaves as a single tunnel SIS-junction, while the temperature dependence of I-cj(T) obeys a power law I-cj(T) = I-cj0(1 - T/T-cj). The critical current density is strongly modified by the application of small magnetic fields. In fact, the application of 5 Oe suppressed I-cj over two orders of magnitude even at temperatures as low as 1.5 K. We also found that the suppression of the amplitude of the superconducting gap parameter within the superconducting islands was found to be negligible in these current-voltage isotherms experiments.