Absence of a True Vortex-Glass Phase above the Bragg Glass Transition Line in Bi-2212

TL;DR

This study investigates vortex behavior in Bi-2212 superconductors, concluding that no true vortex-glass phase exists above the Bragg glass transition line, with vortex motion being plastic at high fields.

Contribution

It provides evidence that the vortex motion above the second peak is plastic and that no vortex glass phase exists at finite temperatures in Bi-2212.

Findings

Vortex motion above the second peak is plastic.

No vortex glass phase exists at finite temperatures in Bi-2212.

The peak of S is due to crossover between meta-stable vortex states.

Abstract

In magnetic measurements on Bi$_2$Sr$_2$CaCu$_2$O$_{8+\delta}$ (Bi-2212) single crystals, a general peak with a dynamical feature on both $S-H$ and $S-T$ curves was found with S the magnetic relaxation rate. At higher fields, the characteristic exponent $\mu$ becomes negative, together with the positive curvature of $logE$ vs. $ logj$ and the scaling based on the 2D vortex glass theory or plastic creep theory, we conclude that the vortex motion above the second peak is plastic when $j\to 0$ and there is no vortex glass phase at finite temperatures in Bi-2212. The peak of S is then explained as the crossover between different meta-stable vortex states.