Regular Article

Magnetoresistance investigation in the mixed state of a high temperature superconductor^★

¹ 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

^* e-mail: bghourmustapha@yahoo.fr; m.bghour@uiz.ac.ma

Received: 7 July 2020
Received in final form: 17 October 2020
Accepted: 3 December 2020
Published online: 21 January 2021

Abstract

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 $R_c^{\parallel }\left(H,T\right)$ is larger than $R_{ab}^{\parallel }\left(H,T\right)$ with anisotropy factor $\gamma =R_c^{\parallel }/R_{ab}^{\parallel }$ 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.