The shape of a moving fluxon in stacked Josephson junctions

TL;DR

This paper investigates the shape and dynamics of a moving fluxon in stacked Josephson junctions, revealing complex structures, unusual magnetic field configurations, and the spectrum of Cherenkov radiation through numerical and analytical methods.

Contribution

It provides a novel analytical and numerical analysis of fluxon shapes in double stacked Josephson junctions, including the discovery of inverted magnetic fields and Cherenkov radiation characteristics.

Findings

Fluxon consists of two components with different velocities and penetration depths.

Fluxon can have an inverted magnetic field in the second junction at high velocities.

Derived an analytical expression for Cherenkov radiation wavelength.

Abstract

We study numerically and analytically the shape of a single fluxon moving in a double stacked Josephson junctions (SJJ's) for various junction parameters. We show that the fluxon in a double SJJ's consists of two components, which are characterized by different Swihart velocities and Josephson penetration depths. The weight coefficients of the two components depend on the parameters of the junctions and the velocity of the fluxon. It is shown that the fluxon in SJJ's may have an unusual shape with an inverted magnetic field in the second junction when the velocity of the fluxon is approaching the lower Swihart velocity. Finally, we study the influence of fluxon shape on flux-flow current-voltage characteristics and analyze the spectrum of Cherenkov radiation for fluxon velocity above the lower Swihart velocity. Analytic expression for the wavelength of Cherenkov radiation is derived.