HALL CONDUCTIVITY SIGN REVERSAL AND FLUCTUATIONS IN YBCO FILMS

We measured resistive transitions of YBCO films in applied fields up t o 9T. The longitudinal fluctuation conductivities obey a scaling law. After separating the AL term from the total fluctuation Hall conductiv ity, the AL Hall conductivity follows the same scaling law, while the MT Hall conductivity does not scale. In addition, the AL and MT terms have opposite sign. At low fields and temperature close to T-c(H), the AL term dominates the MT term, therefore causing the total Hall condu ctivity sign change.