Nature of phase transitions in two-dimensional type-II superconductors

Abstract

We have simulated the thermodynamics of vortices in a thin film of a type-II superconductor. We make the lowest Landau level approximation, and use quasiperiodic boundary conditions. Our work is consistent with the results of previous simulations where evidence was found for an apparent first-order transition between the vortex liquid and the vortex crystal states. We show, however, that these results are just an artifact of studying systems that are too small. There are substantial difficulties in simulating larger systems using traditional approaches. By means of the optimal energy diffusion algorithm, we have been able to study systems containing up to about one thousand vortices, and for these larger systems, the evidence for a first-order transition disappears. By studying both crystalline and hexatic orders, we show that the Kosterlitz-Thouless-Halperin-Nelson-Young (KTHNY) scenario seems to apply where melting from the crystal is first to the hexatic liquid state and next to the normal vortex liquid, in both cases via a continuous transition.

Source-reported materials — not catalogue approval

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