Magnetoresistance investigation in the mixed state of a high temperature superconductor★
Equipe des Matériaux Supraconducteurs à haute température critique, Université Ibn Zohr, Faculté des Sciences, Agadir BP: 8106, Morocco
2 Faculté des Sciences Appliquées, Route Nationale N° 10 cité Azrou, Ait Melloul, Université Ibn Zohr, Morocco
Received in final form: 17 October 2020
Accepted: 3 December 2020
Published online: 21 January 2021
In this work, we analyze the behavior of the magnetoresistance R (H, T) of a high temperature superconductor YBa 2 Cu 3 O 7−δ thin film optimally doped. Measurements of the magnetoresistance were carried out in the mixed state for a magnetic field up to 14 T applied parallel to c − axis then parallel to ab − plane with a dc transport current of 100 and 500 nA, 0.1 and 0.3 mA 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 that is larger than with anisotropy factor depending 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 ) α where H irr (0), T o and α 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.
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