Magnetoresistance Investigation In The Mixed State Of A High Temperature Superconductor

In this work, we analyze the behavior of the magnetoresistance R(H, T) of a high temperature superconductor YBa2Cu3O7-delta thin film optimally doped. Measurements of the magnetoresistance were carried out in the mixed state for a magnetic field up to 14T applied parallel to c-axis then parallel to ab-plane with a dc transport current of 100 and 500nA, 0.1 and 0.3mA perpendicular to the magnetic field direction in both cases. The obtained results show that the magnetoresistance is in a good agreement with the thermally assisted flux creep. However, the magnetoresistance in the flux flow regime cannot be described by the Barden-Stephen model which conjectures another origin of these results. In this sense, the quantum fluctuations of the order parameter is a good alternative to understanding the shape of the magnetoresistance. The comparison of the magnetoresistance of the two directions shows thatR c parallel to(H , T)is larger thanRa bparallel to(H , T)with anisotropy factorgamma =R c parallel to/Ra bparallel todepending on temperature and magnetic field. The irreversibility line H-irr(T) as well as H-C2(T) are determined and the first one is fitted with the phenomenological model H-irr(T)=H-irr(0)(1-T/T-o)(alpha) where H-irr(0), T-o and alpha are parameters obtained from the fit. The investigation of the scaling law allows us to prove that a crossover from 3D to 2D behavior is a feature of our sample which justifies the existence of the decoherence effect.