Lifetime of vortices in two-dimensional easy-plane ferromagnets

We use a combination of classical Monte Carlo and spin dynamics simulations for the two-dimensional (2D) classical easy-plane ferromagnet to estimate the lifetime of free vortices near the Kosterlitz-Thouless transition temperature. The number fluctuations of free vortices are used to calculate the lifetime. The inverse lifetime gives an estimate for a cutoff frequency below which an ideal-gas description of vortex dynamics is inappropriate. We compare the lifetime results with simulations and ideal-gas phenomenology for the dynamic structure function, S^αα(q,ω). Motion of the vortices is observed only on a short-range scale and the magnitude of the lifetime is mainly determined by processes of creation and annihilation of vortex-antivortex pairs rather than by vortex motion. © 1996 The American Physical Society.