Two-dimensional Vortices in Superconductors

TL;DR

This paper investigates the phase transition of vortices in high-temperature superconductors, revealing a field-independent transition temperature from a liquid to a solid vortex phase, which is crucial for enhancing superconductor applications.

Contribution

It demonstrates the existence of a two-dimensional vortex solid phase in Bi-2212 and shows that the transition temperature remains constant at high magnetic fields, confirming theoretical predictions.

Findings

Vortices transition from liquid to solid phase in Bi-2212.

Transition temperature is independent of magnetic field at high fields.

The vortex solid phase is disordered with unexpected threshold behavior.

Abstract

Superconductors have two key characteristics. They expel magnetic field and they conduct electrical current with zero resistance. However, both properties are compromised in high magnetic fields which can penetrate the material and create a mixed state of quantized vortices. The vortices move in response to an electrical current dissipating energy which destroys the zero resistance state\cite{And64}. One of the central problems for applications of high temperature superconductivity is the stabilization of vortices to ensure zero electrical resistance. We find that vortices in the anisotropic superconductor Bi$_{2}$Sr$_{2}$CaCu$_{2}$O$_{8+\delta}$ (Bi-2212) have a phase transition from a liquid state, which is inherently unstable, to a two-dimensional vortex solid. We show that at high field the transition temperature is independent of magnetic field, as was predicted theoretically for the melting of an ideal two-dimensional vortex lattice\cite{Fis80,Gla91}. Our results indicate that the stable solid phase can be reached at any field as may be necessary for applications involving superconducting magnets\cite{Has04,Sca04,COHMAG}. The vortex solid is disordered, as suggested by previous studies at lower fields\cite{Lee93,Cub93}. But its evolution with increasing magnetic field displays unexpected threshold behavior that needs further investigation.