Observation of asymmetric transverse voltage in granular high-Tc superconductors

This work reports the influence of the granularity on the transverse voltage as a function of the temperature, V-XY(T), in polycrystalline samples of Bi2Sr2Ca0.8Pr0.2Cu2O8+delta composition. It is observed nonzero transverse voltage at zero external magnetic field in the vicinity of the superconducting transition while far away from it, both above and below, no such voltage was detected. Measurements of V-XY(T) in both directions of magnetic field allowed to calculate the symmetric and asymmetric transverse voltages in the full range of the applied magnetic field studied (zero up to 9 T). The symmetric transverse voltage as a function of the temperature presents sign reversal of the Hall resistance and positive Hall voltage at normal state such as expected for hole-doped high critical temperature superconductors. On the other hand, the asymmetric component of V-XY(T) shows a peak near the superconducting transition which has been recently reported in literature. V-XY(T) curves measured in a sample with double superconducting transition, which was confirmed by ac-susceptibility measurements and hysteresis loops of the magneto-resistance, present two peaks in the asymmetric component. These peaks are related to the intergranular and intragranular transitions and can be explained within the framework of Josephson and Abrikosov vortices and anti-vortices motion. By comparing the temperature dependence of the asymmetric transverse voltage and the derivative of longitudinal voltage is possible to observe a specific relation between both transport properties, which is noted to be valid not only at zero applied magnetic field but also under applied field. (c) 2004 Elsevier B.V. All rights reserved.