2-DIMENSIONAL ABRIKOSOV-VORTEX MICROCLUSTERS - SHELL STRUCTURE AND MELTING

Melting of two-dimensional Abrikosov-vortex microclusters in a type-II superconductor island with thickness less than the coherence length h as been studied. Equilibrium configurations corresponding to local and global minima of potential energy for clusters with N = 1 - 50 partic les are calculated. The temperature dependences of the structure and o f mean-square radial and angular vortex displacements are investigated . It is shown that vortex microclusters melt in two stages: first the frozen-out phase transfers to a state corresponding to rotational reor ientation of crystalline shells with respect to one another, followed by a transition to a state with no radial order at a substantially hig her temperature. The reason for this is that the barrier to shell rota tion is significantly lower than that to radial breakdown of shells. ( C) 1997 American Institute of Physics.