Nonlocal Josephson diode effect in minimal Kitaev chains

TL;DR

This paper demonstrates a nonlocal Josephson diode effect in a system of three coupled minimal Kitaev chains, showing highly tunable supercurrents with efficiencies over 50%, enabled by asymmetric Andreev spectra.

Contribution

It introduces the realization of a nonlocal Josephson diode effect in minimal Kitaev chains, highlighting the role of symmetry breaking and asymmetric Andreev spectra for supercurrent control.

Findings

Nonlocal Josephson supercurrents with positive and negative critical currents.

Achieved diode efficiencies exceeding 50%.

Controlled by asymmetric Andreev bound states and symmetry breaking.

Abstract

We study the emergence of the nonlocal Josephson effect in a system composed of three laterally coupled minimal Kitaev chains and exploit it to realize the nonlocal Josephson diode effect. We find that an imbalance between crossed Andreev reflections and electron cotunneling in the middle Kitaev chain gives rise to an asymmetric $2\pi$-periodic phase-dependent Andreev spectrum, controlled by the superconducting phases across the left and right junctions. We then show that the asymmetric Andreev spectrum, formed by hybridized Andreev bound states at the left and right junctions, enables a supercurrent across one junction via the phase difference at the other junction, thereby signaling the nonlocal Josephson effect. Notably, these nonlocal Josephson supercurrents exhibit distinct positive and negative critical currents, demonstrating the realization of the nonlocal Josephson diode effect with highly tunable polarity and efficiencies exceeding $50\%$. The nonlocal Josephson diode effect requires breaking local time-reversal and local charge-conjugation symmetries, with the latter being unique to minimal Kitaev chains. Our results establish minimal Kitaev chains as a highly controllable platform for engineering nonlocal Josephson phenomena.