Magnetotransport properties of Hg$_{1 -x}$Re$_{x}$Ba$_{2}$Ca$_{2}$Cu$_{3}$O$_{8 + \delta }$ superconductors

Abstract

Systematic measurements on Hall and longitudinal resistivities as a function of temperature in Hg$_{1 - x}$Re$_{x}$Ba$_{2}$Ca$_{2}$Cu$_{3}O_{8 + \delta }$ (x=0.18) ceramic samples were effectuated. These measurements were performed in magnetic fields H=0, 10, 20, 40 and 50 kOe, applied perpendicularly to the transport current orientation. In the normal phase, the Hall coefficient is positive and may be accurately fitted to $R_H = 1/aT + b$. The Hall angle varies approximately as predicted by Anderson's formula. When the temperature approaches from above the mean-field critical temperature $T_{c}$, the Hall resistivity decreases abruptly as a consequence of thermal fluctuations. Below $T_{c}$ and for $H=10 $and 20 kOe, the Hall response changes signal, going passing through a minimum and becoming positive again before the zero resistance state is obtained. For stronger applied fields, the Hall resistivity remains positive in the mixed phase, though its qualitative shape, preserving the local minimum below $T_{c}$. We ascribe the double sign reversal feature to combined effects of thermal fluctuations and vortex motion. Close to the zero resistance state, the Hall resistivity varies as a power law of the longitudinal resistivity, with a field-independent exponent. This result may be interpreted as evidence of a vortex-glass transition.