A new broken U(1)-symmetry in extreme type-II superconductors

TL;DR

This paper reports a novel phase transition in extreme type-II superconductors involving U(1)-symmetry breaking within the vortex liquid phase, characterized by vortex path connectivity loss and a zero-field counterpart, revealed through large-scale simulations.

Contribution

It uncovers a new symmetry-breaking transition in vortex liquids of superconductors, distinct from vortex lattice melting, with detailed simulation evidence.

Findings

Loss of vortex path number conservation at transition

Vortex line tension drops to zero

Weak specific heat anomaly observed

Abstract

A phase transition within the molten phase of the Abrikosov vortex system without disorder in extreme type-II superconductors is found via large-scale Monte-Carlo simulations. It involves breaking a U(1)-symmetry, and has a zero-field counterpart, unlike vortex lattice melting. Its hallmark is the loss of number-conservation of connected vortex paths threading the entire system {\it in any direction}, driving the vortex line tension to zero. This tension plays the role of a generalized ``stiffness'' of the vortex liquid, and serves as a probe of the loss of order at the transition, where a weak specific heat anomaly is found.