HALL-CONDUCTIVITY SIGN REVERSAL AND FLUCTUATIONS IN YBA2CU3O7-DELTA FILMS

We measured the longitudinal and Hall resistive transitions of YBa2Cu3 O7-delta films in applied fields up to 9 T. The longitudinal fluctuati on conductivities obey the scaling behavior of the three-dimensional H artree fluctuation theory of Ullah and Dorsey. The fluctuation Hall co nductivities do not scale. Our analysis shows that there are substanti al contributions from the Maki-Thompson (MT) process as well as the As lamazov-Larkin (AL) one. Using an ansatz suggested by the microscopic theory of Fukuyama et al., we separated the AL term from the total flu ctuation conductivity. The AL Hall conductivity follows a scaling law, and the AL and MT terms have opposite sign. The sign of the AL term i s consistent with the sign change in the flux-flow regime, as predicte d by theory. At low fields and temperatures just above T-c(H), the AL term dominates the MT term, therefore causing the total Hall-conductiv ity sign change.