Decoupled two-dimensional superconductivity and continuous melting transitions in layered superconductors immersed in a parallel magnetic field

TL;DR

This study uses Monte Carlo simulations to explore the phase diagram of layered superconductors under parallel magnetic fields, revealing a novel decoupled 2D superconducting phase and characterizing the melting transitions as Kosterlitz-Thouless and second-order.

Contribution

It uncovers a new intermediate decoupled 2D phase in layered superconductors and characterizes the nature of phase transitions, including a KT transition, in the B-T phase diagram.

Findings

Identification of a decoupled 2D quasi-long-range ordered phase at high fields and anisotropy.

Confirmation that the melting transition of the 2D vortex lattice is of Kosterlitz-Thouless type.

The phase diagram features a multicritical point where three phases meet.

Abstract

Possible phases and the B-T phase diagram of interlayer Josephson vortices induced by a magnetic field parallel to the superconducting layers are investigated by Monte Carlo simulations based on the anisotropic, frustrated XY model. While for low magnetic fields and small anisotropy parameters a single first-order transition is observed similarly to the melting of Abrikosov (or pancake) vortex lattice, an intermediate phase, characterized by decoupled, two-dimensional (2D) quasi long-range crystalline order (QLRCO) and superconductivity, is found at high magnetic fields and large anisotropy parameters. Combining the simulation results with a symmetry argument, it is revealed that this intermediate phase is of Kosterlitz-Thouless (KT) type, and the melting of 2D quasi Josephson vortex lattices and suppression of superconductivity is a KT transition. Evolution of the intermediate phase to the low-temperature phase of 3D LRCO is second order and belongs to the 3D XY universality class. The three phase boundaries merge at a multicritical point. It is revealed that decoupling of the 3D Josephson vortex lattice into the 2D phase is triggered by hops of Josephson flux lines across superconducting layers activated by thermal fluctuations. The equilibrium phase diagram with the KT phase at high magnetic fields and large anisotropy parameters is consistent with the peculiar Lorentz-force-independent dissipation observed in highly anisotropic high-Tc superconductor Bi2Sr2CaCu2O(8+y) by Iye et al. (Physica 159C, 433 (1989)).