Effect of random pinning on nonlinear dynamics and dissipation of a vortex driven by a strong microwave current

TL;DR

This paper uses numerical simulations to study how random pinning affects the nonlinear dynamics and energy dissipation of vortices in superconducting films under strong microwave currents, revealing complex mesoscopic fluctuations and potential instabilities.

Contribution

It introduces a detailed numerical analysis of vortex behavior considering various pinning types and the Larkin-Ovchinnikov drag, highlighting mesoscopic effects and nonlinear dissipation mechanisms.

Findings

Local residual surface resistance exhibits strong mesoscopic fluctuations.

Global surface resistance increases smoothly with field and levels off.

Nonmonotonic resistance behavior and vortex instabilities can occur due to pinning and vortex velocity effects.

Abstract

We report numerical simulations of a trapped elastic vortex driven by a strong ac magnetic field $H(t)=H\sin\omega t$ parallel to the surface of a superconducting film. The surface resistance and the power dissipated by an oscillating vortex perpendicular to the film surface were calculated as functions of $H$ and $\omega$ for different spatial distributions, densities, and strengths of pinning centers, including bulk pinning, surface pinning, and cluster pinning. Our simulations were performed for both the Bardeen-Stephen viscous vortex drag and the Larkin-Ovchinnikov (LO) drag coefficient $\eta(v)$ decreasing with the vortex velocity $v$. The local residual surface resistance $R_i(H)$ calculated for different statistical realizations of the pinning potential exhibits strong mesoscopic fluctuations caused by local depinning jumps of a vortex segment as $H$ increases, but the global surface resistance $\bar{R}_i(H)$ obtained by averaging $R_i(H)$ over different pin configurations increases smoothly with the field amplitude at small $H$ and levels off at higher fields. For strong pinning, the LO decrease of $\eta(v)$ with $v$ can result in a nonmonotonic field dependence of $R_i(H)$ which decreases with $H$ at higher fields, but cause a runaway instability of the vortex in a thick film for weak pinning. It is shown that overheating of a single moving vortex can produce the LO-like velocity dependence of $\eta(v)$, but can mask the decrease of the surface resistance with $H$ at a higher density of trapped vortices.