On the Nature of the Phase Transition Triggered by Vortex-Like Deffects in the 2D Ginzburg-Landau Model

Abstract

The two dimensional lattice Ginzburg-Landau hamiltonian is simulated numerically for different values of the coherence length $\hat{I}¾$ in units of the lattice spacing $a$, a parameter which controls amplitude fluctuations. The phase diagram on the plane $T-\hat{I}¾$ is measured. Amplitude fluctuations change dramatically the nature of the phase transition: for values of $\hat{I}¾/a\simeq 1$, instead of the smooth Kosterlitz-Thouless transition there is a {\em first order} transition with a discontinuity in the vortex density $v$ and a sharper drop in the helicity modulus $\hat{I}“$. Both observables $v$ and $\hat{I}“$ are analyzed in detail at the crossover region between first and second order which occurs for intermediate values of $\hat{I}¾/a$.

9 pages, 7 postscript (eps) figures