Anomalous vortex dynamics in 2D superconductors

Abstract

Low -frequency dynamic impedance ($\sigma^{-1}(\omega,T)\equiv(\sigma_{1}+i\sigma_{2})^{-1}$) measurements on Josephson junction arrays with finite vortex screening length $\xi$, found that $\sigma_{1}\sim |\log{\omega}|$, $\sigma_{2}\sim$ constant. This implies anomalously sluggish vortex mobilities $\mu_{V}(\omega)\sim\sigma_{1}^{-1}$, and is in conflict with general dynamical scaling expressions that yield, for low-$\omega$, $\sigma_{1}\rightarrow\xi^{2}$ and $\sigma_{2}\rightarrow 0$. We calculate : a) $\sigma(\omega,T)$ by real-space vortex scaling; b) $\mu_{V}(\omega)$ using Mori's formalism for a screened Coulomb gas. We find, in addition to the usual critical (large-$\omega$) and hydrodynamic (low-$\omega$) regimes, a new intermediate-frequency scaling regime into which the experimental data fall. This resolves the above mentioned conflict and makes explicit predictions for the scaling form of $\sigma(\omega,T)$, testable in SNS and SIS arrays.