Magnetoresistance investigation in the mixed state of a high temperature superconductor
In this work we analyze the behavior of magnetoresistance R(H,T) of a high temperature superconductor YBa2Cu3O7-delta thin film optimally doped. Measurements of magnetoresistance were carried out in the mixed state for a magnetic field up to 14T applied in the 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 conjecture another origin of these results. In this sense, the quantum fluctuations of the order be parameter is a good alternative to understanding the shape of the magnetoresistance. The comparison of the magnetoresistance of the two directions shows that Rc(H,T) is larger than Rab(H,T) with anisot-ropy factor gamma=Rc/Rab depending on temperature and magnetic field. The irreversibility line Hirr(T) as well as Hc2(T) are determined and the first one is adjusted with the phenomenological model Hirr(T)=Hirr(0)(1-T/T0)^alpha where Hirr(0), T0 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.