Equilibrium First-Order Melting and Second-Order Glass Transitions of the Vortex Matter in Bi$_2$Sr$_2$CaCu$_2$O$_8$

TL;DR

This study maps the complex phase diagram of vortex matter in Bi$_2$Sr$_2$CaCu$_2$O$_8$, revealing first- and second-order transitions and four distinct phases through equilibrium magnetization measurements.

Contribution

It provides the first detailed thermodynamic phase diagram showing both first- and second-order vortex transitions in Bi$_2$Sr$_2$CaCu$_2$O$_8$ using equilibrium magnetization data.

Findings

Identification of two sharp first-order magnetization steps indicating a liquid-solid-liquid sequence.

Detection of a second-order glass transition line from a slope change in equilibrium magnetization.

Evidence for four distinct vortex phases: Bragg glass, vortex crystal, glass, and liquid.

Abstract

The thermodynamic $H-T$ phase diagram of Bi$_2$Sr$_2$CaCu$_2$O$_8$ was mapped by measuring local \emph{equilibrium} magnetization $M(H,T)$ in presence of vortex `shaking'. Two equally sharp first-order magnetization steps are revealed in a single temperature sweep, manifesting a liquid-solid-liquid sequence. In addition, a second-order glass transition line is revealed by a sharp break in the equilibrium $M(T)$ slope. The first- and second-order lines intersect at intermediate temperatures, suggesting the existence of four phases: Bragg glass and vortex crystal at low fields, glass and liquid at higher fields.