Numerical studies of the phase diagram of layered type-II superconductors in a magnetic field

[摘要] We report on simulations of layered superconductors using the Lawrence-Doniach model in the framework of the lowest-landau-level approximation. We find a first-order phase transition with a B(T) dependence which agrees very well with the experimental melting line in YBa2Cu3O7-delta. The transition is not associated with vortex lattice melting, but separates two vortex liquid states characterized by different degrees of short-range crystalline order and different length scales of correlations between vortices in different layers. The transition line ends at a critical end point at low fields. We find the magnetization discontinuity and the location of the lower critical magnetic field to be in good agreement with experiments in YBa2Cu3O7-delta. Length scales of order parameter correlations parallel and perpendicular to the magnetic field increase exponentially as 1/T at low temperatures. The dominant relaxation time scales grow roughly exponentially with these correlation lengths. The consistency of our numerical results with various experimental features in YBa2Cu3O7-delta, including the dependence on anisotropy, and the temperature dependence of the structure factor at the Bragg peaks in neutron scattering experiments is demonstrated. [S0163-1829(99)02933-1].

[关键词] LATTICE MELTING TRANSITION;T-C SUPERCONDUCTORS;HIGH-TEMPERATURE SUPERCONDUCTORS;YBA2CU3O7 SINGLE-CRYSTALS;ANGLE NEUTRON-SCATTERING;MONTE-CARLO SIMULATION;VORTEX-LINE LIQUID;FLUX-LATTICE;UNTWINNED YBA2CU3O7-DELTA;THERMAL FLUCTUATIONS