Regular Article

The activation energy U(T,B) in high temperature superconductor^★

¹ Équipe des Matériaux Supraconducteurs à Haute Température Critique, Université Ibn Zohr, Faculté des Sciences, BP: 8106, Agadir, Maroc
² Université Ibn Zohr, Faculté des Sciences Appliquées, Route Nationale N° 10 cité Azrou, Ait Melloul, Maroc
³ Université Chouaib-Doukkali, LabSIPE, Ecole Nationale des Sciences Appliquées, El Jadida, Route Nationale N° 1 (Route Azemmour), Km 6, Elhaouzia, BP: 1166 El Jadida Plateau 24002, Maroc

^* e-mail: a.labrag@uiz.ac.ma

Received: 7 July 2020
Received in final form: 26 August 2020
Accepted: 15 September 2020
Published online: 2 November 2020

Abstract

It is reported in this paper on the thermally assisted flux flow in epitaxial YBa₂Cu₃O_7-δ deposited by Laser ablation method on the SrTiO₃ substrate. The resistivity measurements ρ (T, B) of the sample under various values of the magnetic field up to 14T in directions B_∥ab-plane and B_∥c-axis with a dc weak transport current density were investigated in order to determine the activation energy and then understand the vortex dynamic phenomena and therefore deduce the vortex phase diagram of this material. The apparent activation energy U₀ (B) calculated using an Arrhenius relation. The measured results of the resistivity were then adjusted to the modified thermally assisted flux flow model in order to account for the temperature-field dependence of the activation energy U (T, B). The obtained values from the thermally assisted activation energy, exhibit a behavior similar to the one showed with the Arrhenius model, albeit larger than the apparent activation energy with ∼1.5 order on magnitude for both cases of the magnetic field directions. The vortex glass model was also used to obtain the vortex-glass transition temperature from the linear fitting of [d ln ρ/dT ] ⁻¹ plots. In the course of this work thanks to the resistivity measurements the upper critical magnetic field H_c2 (T), the irreversibility line H_irr (T) and the crossover field H_CrossOver (T) were located. These three parameters allowed us to establish a phase diagram of the studied material where limits of each vortex phase are sketched in order to optimize its applicability as a practical high temperature superconductor used for diverse purposes.