Magnetic torque study of the temperature dependent anisotropy parameter in overdoped superconducting single-crystal YBa_2Cu_3O_7

TL;DR

This study investigates how the anisotropy parameter of overdoped YBa2Cu3O7 superconductors varies with temperature near T_c using torque magnetometry and models accounting for vortex core effects.

Contribution

It provides detailed measurements of the temperature dependence of anisotropy parameters in overdoped YBa2Cu3O7, incorporating vortex core effects into the analysis.

Findings

An out-of-plane anisotropy parameter around 6.5 that increases slightly as temperature decreases.

A temperature-independent in-plane anisotropy parameter gamma_ab of approximately 1.12.

Both models used yielded consistent results for the anisotropy parameters.

Abstract

An overdoped YBa2Cu3O7 single crystal was studied by SQUID and torque magnetometry in order to investigate the temperature dependence of the anisotropy parameter close to the transition temperature T_c (0.87 T_c < T < T_c). Angle dependent torque measurements were performed and analyzed with the widely used Kogan model [Phys. Rev. B 38, 7049 (1988)] as well as with an extended model by Hao and Clem [Phys. Rev. Lett. 67, 2371 (1991)], taking into account the influence of the vortex cores on the magnetization. Both approaches yield similar results, with an out-of-plane anisotropy parameter around 6.5 which slightly increases with decreasing temperature, and a temperature independent in-plane anisotropy parameter gamma_ab}= 1.12(5).