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

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, $ϕ_i$, is fixed for each of the FS states. In the $m$-th FS state the value of $ϕ_i$ is equal to an integer amount of flux quanta, $ϕ_i =mϕ_0$. Two types of single Josephson vortices carrying fluxes $ϕ_0$ or/and $ϕ_0/2$ 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.