Non-solitary determination of vortex-glass transition temperatures in YBa2Cu3O7−δ superconducting thin films

Abstract By accomplishing DC transport and magnetic sweep measurement on high quality YBa 2 Cu 3 O 7−δ superconducting thin films, we obtained E-j characteristic curves in a very large dynamic region (with E varied from 10 to 10 −7 V/m). The data unambiguously show that, both positive curvature and negative curvature coexist in one double logarithmic curve log(E) versus log(j) at a fixed temperature and magnetic field. This indicates that the so-called vortex-glass transition temperature T g as defined by the crossover temperature from negative curvature to positive curvature depends on the accessible electric field window. Further analyses show that our transport data can be approximately interpreted by the conventional flux-creep model. Finally we propose a model which shows that the flux motion can be changed from collective-creep or glassy behavior to the so-called thermally-assisted-flux-flow (TAFF) behavior by lowering the current.