Vortex-system ordering during magnetisation measurements in YBa2Cu3O7−δ films at low temperatures

Zero-field-cooling dc magnetisation relaxation measurements performed on optimally doped epitaxial YBa2Cu3O7?? films with the external magnetic field H oriented parallel to the c-axis reveal the ordering of the creeping vortex-system in the low temperature T domain, due to the macroscopic currents induced in the sample. This dynamic ordering manifests itself through the appearance of a maximum in the T variation of the normalised vortex-creep activation energy. The location of this maximum in the H?T plane describes a well-defined current induced order?disorder line. Our results suggest the absence of a static elastic vortex glass in disordered high-temperature superconductors at high H, and the current induced ordering of the vortex-system as a possible origin for the current?voltage characteristic scaling in terms of an elastic vortex glass?vortex liquid transition