Hall effect and longitudinal conductivity in a Hg0.82Re0.18Ba2Ca2Cu3O8+delta superconductor

We report on the Hall effect and longitudinal electrical conductivity measu rements in a polycrystalline bulk sample of a Hg0.82Re0.18Ba2Ca2Cu3O8+delta superconductor, with T-c congruent to 133 K. The experiments are performed as a function of the temperature in fixed magnetic fields ranging from 0 t o 5 T. In the normal phase, the Hall resistivity is hole-like and inversely proportional to the temperature. In the mixed phase and when the applied f ield is below mu H-0 = 2 T, the Hall resistivity shows a double sign revers al. For fields above 2 T, the Hall resistivity remains positive, although q ualitatively showing the trends observed at low fields. We attribute this b ehaviour to two independent contributions with opposite sign. A negative te rm due to thermal fluctuations is relevant near T, whereas a positive contr ibution related to vortex motion dominates at lower temperatures. Near the zero resistance state, the Hall resistivity varies as a power law of the lo ngitudinal resistivity, with a field independent exponent beta congruent to 1.5. Analysis of the fluctuation contribution to the longitudinal conducti vity reveals the occurrence of a large two-dimensional Gaussian regime prec eding the pairing transition at T, However, in a short temperature interval immediately above T, the fluctuation conductivity scales as predicted by t he three-dimensional XY model, with a dynamic critical exponent z = 3/2. At zero applied field and near the zero-resistance state, the fluctuation con ductivity behaviour indicates the occurrence of a coherence transition, whe re the fluctuating phases of individual superconducting grains become long- range ordered. A strong enlargement of the temperature interval with non-ze ro resistance in the mixed-state is produced by the application of the magn etic field.