Nonlinear dynamics of Josephson vortices in a film screen under dc and ac magnetic fields

TL;DR

This paper uses numerical simulations to analyze how Josephson vortices behave under combined dc and ac magnetic fields in superconducting thin films, revealing their impact on nonlinear surface resistance.

Contribution

It provides new insights into vortex dynamics under complex magnetic fields and evaluates their effects on superconducting surface resistance.

Findings

Threshold magnetic field depends on frequency.

Power dissipation varies with ac field amplitude and frequency.

Weak-linked grain boundaries influence nonlinear surface resistance.

Abstract

We present detailed numerical simulations of Josephson vortices in a long Josephson junction perpendicular to a thin film screen under strong dc and ac magnetic fields. By solving the sine-Gordon equation, we calculated the threshold magnetic field for penetration of fluxons as a function of frequency, and the power dissipated by oscillating fluxons as functions of the ac field amplitude and frequency. We considered the effects of superimposed ac and dc fields, and a bi-harmonic magnetic field resulting in a vortex ratchet dynamics. The results were used to evaluate the contribution of weak-linked grain boundaries to the nonlinear surface resistance of polycrystalline superconductors under strong electromagnetic fields, particularly thin film screens and resonator cavities.