TRANSPORT AND MAGNETIC-PROPERTIES OF POLYCRYSTALLINE SM2-XCEXCUO4-Y

A systematic study of transport and magnetic properties of polycrystalline Sm2-xCecCuO4-y (0.15 less-than-or-equal-to x much less than 0.18) specimens obtained from a sol-gel precursor reveals a striking double resistive superconducting transition. One of the resistive transitions takes place at a temperature T(ci) and is almost insensitive to Ce concentration, applied magnetic field, and current density, while the other transition occurs at a lower temperature T(cj) and is very sensitive to Ce content, applied magnetic field, and current density. Alternating-current magnetic susceptibility chi(ac) measurements reveal two interesting features. There is only one contribution to the diamagnetic signal below approximately 20 K, which is particularly evident in the resistive component chi'' of chi(ac) where a peak at T(cj) can be identified. The application of an applied magnetic field shifts the chi'' peak to lower temperatures and reveals a spin-glass-like behavior. All the results can be satisfactorily explained in terms of weakly linked Josephson junctions between small superconducting islands. The small islands have a superconducting transition at a higher temperature T(ci), and the long-range phase coherence is achieved through Josephson coupling at lower temperatures T(cj). All the results suggest a superconducting glass state in a disordered Josephson network.