MAGNETIC-FIELD DEPENDENCE OF THE CRITICAL-DYNAMICS OF A SUPERCONDUCTING YBA2CU3O7-DELTA DETWINNED SINGLE-CRYSTAL

The in-plane longitudinal resistivities rho(aa) and rho(bb) Of a singl e-crystal of YBa2Cu3O7-delta have been measured as a function of magne tic field H (less than 6.75 T) and temperature T near T-c. We found th at the rho(aa)(T,H) data in the mixed state collapse into a single cur ve as a function of rho(bb)(T,H). The extracted fluctuation conductivi ty exhibits dynamic scaling over a wide range of T and H: assuming tha t the static universality class is the three-dimensional XY model yiel ds the observed dynamic critical exponent, z=1.5 +/-0.1 (H>0), apparen tly consistent with the dynamic universality class of superfluid He-4. In zero field, the data are inconclusive, and a reliable determinatio n of z is not possible.