MAGNETOTRANSPORT PROPERTIES OFGdBa2Cu3O7 - δSUPERCONDUCTING THIN FILMS

Systematic measurements of the Hall and longitudinal resistivities as a function of temperature inGdBa2Cu3O7 - δthin films were effectuated. These were performed in magnetic fieldsB = 0, 1, 2, 3, 4and 5 T, applied perpendicular to the transport current orientation. Films were prepared by anin-situhigh-pressure dc-sputtering technique in an atmosphere of pure oxygen. In the normal phase, the Hall coefficient is positive and varies inversely proportional to temperature. The Hall angle changes approximately as predicted by Anderson's formula. When the temperature approaches the mean-field critical temperatureTcfrom above, the Hall resistivity decreases abruptly in consequence of thermal fluctuations. BelowTcthe Hall response changes signal, goes through a minimum and vanishes when the zero resistance is attained. We ascribe the 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.