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 single-crystal of YBa2Cu3O7-delta have been measured as a function of magnetic field H (less than 6.75 T) and temperature T near T-c. We found that the rho(aa)(T,H) data in the mixed state collapse into a single curve as a function of rho(bb)(T,H). The extracted fluctuation conductivity exhibits dynamic scaling over a wide range of T and H: assuming that the static universality class is the three-dimensional XY model yields the observed dynamic critical exponent, z=1.5 +/-0.1 (H>0), apparently consistent with the dynamic universality class of superfluid He-4. In zero field, the data are inconclusive, and a reliable determination of z is not possible.