High-field vortices in Josephson junctions with alternating critical current density

TL;DR

This paper investigates long Josephson junctions with alternating critical current density, revealing new equilibrium states called FS states that occur at specific resonant magnetic fields and involve unique vortex configurations.

Contribution

It introduces the concept of field synchronized (FS) states in Josephson junctions with alternating critical current density, detailing their conditions and vortex structures.

Findings

Existence of FS states at specific resonant fields

Presence of vortices carrying flux quanta and half-quanta

Stepwise resonances in current-voltage characteristics

Abstract

We study long Josephson junctions with the critical current density alternating along the junction. New equilibrium states, which we call the field synchronized or FS states, are shown to exist if the applied field is from narrow intervals centered around equidistant series of resonant fields, $H_m$. The values of $H_m$ are much higher than the flux penetration field, $H_s$. The flux per period of the alternating critical current density, $\phi_i$, is fixed for each of the FS states. In the $m$-th FS state the value of $\phi_i$ is equal to an integer amount of flux quanta, $\phi_i =m\phi_0$. Two types of single Josephson vortices carrying fluxes $\phi_0$ or/and $\phi_0/2$ can exist in the FS states. Specific stepwise resonances in the current-voltage characteristics are caused by periodic motion of these vortices between the edges of the junction.