FLUX CREEP AND CRITICAL CURRENTS IN OXIDE SUPERCONDUCTORS

The non-dissipative current that superconductors can carry in the presence of a magnetic field originates from pinning interactions between fluxoids and inhomogeneities in superconductors called pinning centers. However, the non-dissipative persistent current decays logarithmically in time due to a thermal activation of fluxoids trapped in pinning potentials, i.e., the flux creep. It happens also that the critical current density (Jc), the maximum density of the non-dissipative current is even reduced to zero at high magnetic fields. The boundary between zero and nonzero Jcs in the temperature-magnetic field plane is called the irreversibility line. The effects of the flux creep on the irreversibility line and the decreasing rate of the persistent current are quantitatively investigated in association with the strength of the flux pinning. A discussion is given on the possibility of application of oxide superconductors at liquid nitrogen temperature. The correlation between the broad resistive transition in oxide superconductors and the flux creep is also discussed. © 1990.