Screening in Josephson-junction ladders

Ing-Jye Hwang; Seungoh Ryu; D. Stroud

doi:10.1103/PhysRevB.53.R506

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Screening in Josephson-junction ladders

Ing-Jye Hwang, Seungoh Ryu, D. Stroud

DOI 10.1103/PhysRevB.53.R506 · Physical Review B

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Abstract

Both critical current and Shapiro steps in Josephson ladders are found to show effects of vortex exclusion below a critical magnetic field. Vortices are excluded even though the flux itself is not screened out. When current is injected perpendicular to the ladder edges, the critical current is unchanged from its f=0 value up to a penetration field of fc1⊥≈0.12 flux quanta per plaquette. Similarly, there are only integer Shapiro steps below a critical fc1⊥*, where vortices first penetrate. A narrower critical current plateau also appears to form near f=12. No such plateaus occur when current is injected in the parallel direction. We attribute the exclusion in the perpendicular geometry to screening currents which flow along the edges of the ladder.