Weak-link behaviour of Cu_1−xTl_xBa₂Ca₃Cu₄O_12−y superconductor thin films

The weak link behaviour of Cu_1−xTl_xBa₂Ca₃Cu₄O_12−y superconductor thin films has been studied by magnetoresistance and ac-susceptibility measurements. The polycrystalline thin film samples constituting an array of weak links are decoupled with an increase in the external magnetic field. The carriers under the external magnetic field are found to cross these barriers, with activation energies 0.244–0.128 eV. Analysis of the data of the imaginary part of ac-susceptibility at the peak value revealed that the weak links are insulating and make a Josephson array of superconductor–insulator–superconductor (SIS) junctions. Thin insulating grain boundary junctions provide a larger surface area to the shielding currents and hence increase the critical current density of the films.