J. Roa-rojas et al., Hall effect and longitudinal conductivity in a Hg0.82Re0.18Ba2Ca2Cu3O8+delta superconductor, SUPERCOND S, 14(11), 2001, pp. 898-903
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.