Visualizing a dilute vortex liquid to solid phase transition in a Bi2Sr2CaCu2O8 single crystal

TL;DR

This study uses magneto-optical imaging to observe a vortex liquid to solid phase transition in Bi2Sr2CaCu2O8, revealing phase boundaries, coexistence regimes, and the influence of pinning, aligning with theoretical predictions.

Contribution

It provides experimental evidence of vortex phase transitions and phase diagram features in Bi2Sr2CaCu2O8, including the effects of pinning and theoretical fitting of phase boundaries.

Findings

Identification of vortex density jump at phase transition

Demonstration of phase coexistence regime

Fitting phase boundaries with theoretical models

Abstract

Using high sensitivity magneto-optical imaging we find evidence for a jump in local vortex density associated with a vortex liquid to solid phase transition just above the lower critical field in a single crystal of Bi2Sr2CaCu2O8. We find the regions of the sample where the jump in vortex density occurs are associated with low screening currents. In the field - temperature vortex phase diagram we identify phase boundaries demarcating a dilute vortex liquid phase and the vortex solid phase. The phase diagram also identifies a coexistence regime of the dilute vortex liquid and solid phases and shows the effect of pinning on the vortex liquid to solid phase transition line. We find the phase boundary lines can be fitted to the theoretically predicted expression for the low-field portion of the phase boundary delineating a dilute vortex solid from a vortex liquid phase. We show that the same theoretical fit can be used to describe the pinning dependence of the low-field phase boundary lines provided a dependence of the Lindemann number on pinning strength is considered.