Theory of 4e versus 2e supercurrent in frustrated Josepshon-junction rhombi chain

Abstract

We consider a chain of Josepshon-junction rhombi (proposed originally in \cite{Doucot}) in quantum regime, and in the realistic case when charging effects are determined by junction capacitances. In the maximally frustrated case when magnetic flux through each rhombi ${\Phi }_r$ is equal to one half of superconductive flux quantum ${\Phi }_0$, Josepshon current is due to correlated transport of {\em pairs of Cooper pairs}, i.e. charge is quantized in units of $4e$. Sufficiently strong deviation $\delta \Phi \equiv |{\Phi }_r-{\Phi }_0/2|>\delta {\Phi }^c$ from the maximally frustrated point brings the system back to usual $2e$-quantized supercurrent. We present detailed analysis of Josepshon current in the fluctuation-dominated regime (sufficiently long chains) as function of the chain length, $E_J/E_C$ ratio and flux deviation $\delta \Phi$. We provide estimates for the set of parameters optimized for the observation of $4e$-supercurrent.

23 pages, 9 figures

References in corpus (3)

• Persistent current in superconducting nanorings
• Discrete non-Abelian gauge theories in two-dimensional lattices and their realizations in Josephson-junction arrays
• Topological order in the insulating Josephson junction array

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