Anomalous Hall Effect of YBa 2 Cu 3 O 7-δ in the Low-Magnetic-Field Limit

The Hall effect of YBa 2 Cu 3 O 7-δ epitaxial films in the vicinity of superconducting transition was studied under ultra low magnetic fields down to 10-3 T where some field-induced extrinsic effects, such as the reduction and broadening of the transition temperature and the enhancement of fluctuation, can be neglected. The Hall sign reversal was still observed down to the lowest field we arrived, which shows that any mechanism connected with above mentioned extrinsic changes cannot be responsible for the effect. The Hall resistivity ρxy, Hall angle tan α and Hall conductivity σxy are all simply proportional to the magnetic field, resembling the behaviors of the ordinary Hall effect in the low-magnetic-field limit. The temperature range with observable negative Hall resistivity coincides with the critical fluctuation region. These behaviors shows that the negative Hall effect cannot be understood in the picture of flux flow.