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