Vortex dynamics in two-dimensional Josephson junction arrays

The dynamic response of two-dimensional Josephson junction arrays close to, but above the Berezinskii-Kosterlitz-Thouless (BKT) transition temperature is described in terms of the vortex dielectric function epsilon(omega) and the flux noise spectrum S-phi(omega). They are calculated by considering both the contributions of free vortices interacting through a screened Coulomb potential and the pair motion of vortices that are closer to each other than the BKT correlation length. This procedure allows us to understand various anomalous features in epsilon(omega) and in S-phi(omega) that have been observed both experimentally and in dynamic simulations.