Magnetic field and current density dependence of the mixed-state Hall effect in Bi₂Sr₂CaCu₂O_x

We report on measurements of the mixed-state Hall effect in Bi/sub 2/Sr/sub 2/CaCu/sub 2/O/sub x/ thin films in magnetic fields ranging from B=60 mT to B=1 T and current densities j up to 3 MA cm/sup -2/. To reduce the problem of sample heating, we employed a pulsed current technique and developed a new heating correction procedure. We observe a double sign reversal of the Hall resistivity rho /sub yx/ in the mixed state, resulting in two peaks which both depend on B and j. The position of the sign changes only varies with B, but is found to be independent of j. The Hall conductivity sigma /sub xy/ turns positive again in the superconducting regime and dramatically increases towards lower temperatures and current densities, as the pinning is reduced by intense currents.