OBSERVATION OF STEP STRUCTURES IN THE I-V CHARACTERISTICS OF YBCO THIN-FILMS

Many electrical properties of the high Tc superconductors are widely p robed utilizing current-voltage characteristics because of its sensiti vity to the phase transition. In this work we report on detailed study of YBCO I-V characteristics shape above the critical current in the p hase transition vicinity. For a given temperature controlled to a bett er than 10mK stability over the whole I-V cycle, the applied current h as been gradually increased to exceed the critical current. The system has thus been driven to cross over to the mixed state. Using dI/dV ve rsus V plots, it is shown that all the curves are characterized by a f ine step structures at current densities higher than the critical ones .