Single-vortex-induced voltage steps in Josephson-junction arrays

TL;DR

This study combines numerical and analytical methods to explore voltage steps caused by single vortices in Josephson-junction arrays under ac+dc drive, revealing phase-locking, period doubling, and fractional steps, with implications for experiments.

Contribution

It provides a detailed analysis of vortex-induced voltage steps, including new insights into vortex dynamics and fractional steps in Josephson-junction arrays.

Findings

Single-vortex steps correspond to vortex phase-locking.

Period doubling occurs in underdamped arrays.

Fractional voltage steps are observed with vortex-antivortex pairs.

Abstract

We have numerically and analytically studied ac+dc driven Josephson-junction arrays with a single vortex or with a single vortex-antivortex pair present. We find single-vortex steps in the voltage versus current characteristics (I-V) of the array. They correspond microscopically to a single vortex phase-locked to move a fixed number of plaquettes per period of the ac driving current. In underdamped arrays we find vortex motion period doubling on the steps. We observe subharmonic steps in both underdamped and overdamped arrays. We successfully compare these results with a phenomenological model of vortex motion with a nonlinear viscosity. The I-V of an array with a vortex-antivortex pair displays fractional voltage steps. A possible connection of these results to present day experiments is also discussed.