ANALYSIS OF CROSSOVER PHENOMENA IN THE PARACONDUCTIVITY OF YBCO THIN-FILMS OBTAINED BY LASER-ABLATION

We present paraconductivity measurements on YBCO thin films obtained b y means of pulsed laser ablation in MBE condition. The films, grown in different oxygen pressure, exhibit critical temperatures ranging from 81 to 91 K. The excess conductivity was analyzed in order to study cr itical phenomena. We observe the Lawrence-Doniach crossover and, at hi gher temperatures, the crossover related to the breakdown of the Ginzb urg-Landau approximation, due to the importance of short wave fluctuat ions; the first crossover shifts to lower temperatures as the critical temperature of the film decreases, while the second occurs for all th e samples roughly at the same reduced temperature, which proves the un iversality of the paraconductivity behaviour.