THE TRANSPORT-PROPERTIES OF YBA2CU3O7-X THIN-FILMS

YBa2Cu3O7-x thin films with good crystallinity of thickness from 150 to 750 angstrom have been deposited by laser ablation. The resistive transitions of these thin films in a magnetic field, H, were found to follow the expression of the thermally activated flux motion, R = R0 exp[-U0(H, T)/T], where the activation energy, U0(H, T) = U(H)(1 - T/T(c)(H))2 with the transition temperature, T(c)(H), and U(H) approximately H(-alpha). T(c)(H) can be determined by fitting the resistive transitions data. The values of dH(c2)/dT inferred from T(c)(H) for H parallel to the c-axis were close to the values deduced from the scaling law of fluctuation theory. A cross-over of the values of alpha from 0.5 at low field to 1.0 at high field were observed for H parallel to the c-axis. The functional dependence of U(H) is compared with the results from superlattices.