Spin-asymmetric Josephson effect

TL;DR

This paper predicts a spin-asymmetric Josephson effect in ultracold Fermi gases, where spin components of Cooper pairs oscillate with different amplitudes under asymmetric driving, revealing limitations of the bosonic pair tunnelling description.

Contribution

It introduces the concept of a spin-asymmetric Josephson effect and provides a new interpretation based on interference in Rabi oscillations, expanding understanding of Josephson phenomena.

Findings

Spin-up and spin-down components oscillate at the same frequency with different amplitudes.

Standard bosonic pair tunnelling description is insufficient.

Interference in Rabi oscillations explains the asymmetry.

Abstract

The Josephson effect is a manifestation of the macroscopic phase coherence of superconductors and superfluids. We propose that with ultracold Fermi gases one can realise a spin-asymmetric Josephson effect in which the two spin components of a Cooper pair are driven asymmetrically - corresponding to driving a Josephson junction of two superconductors with different voltages V_\uparrow and V_\downarrow for spin up and down electrons, respectively. We predict that the spin up and down components oscillate at the same frequency but with different amplitudes. Our results reveal that the standard description of the Josephson effect in terms of bosonic pair tunnelling is insufficient. We provide an intuitive interpretation of the Josephson effect as interference in Rabi oscillations of pairs and single particles, the latter causing the asymmetry.