Anomalous Josephson Effect in magnetic Josephson junctions with noncentrosymmetric superconductors

TL;DR

This paper demonstrates that noncentrosymmetric superconductors with two-band structures exhibit an anomalous Josephson effect with a tunable phase difference, revealing new states and insights into supercurrent mechanisms.

Contribution

It introduces the concept of an anomalous Josephson current in noncentrosymmetric superconductor junctions and explores the effects of two-band structures and magnetization on supercurrent behavior.

Findings

Anomalous Josephson current appears at zero phase difference.

Tunable ground-state phase difference via ferromagnet parameters.

Discovery of novel states with supercurrents carried by propagating states.

Abstract

We show that the two-band nature of noncentrosymmetric superconductors leads naturally to an anomalous Josephson current appearing at zero phase difference in a clean noncentrosymmetric superconductor/ferromagnet/noncentrosymmetric superconductor junction. The two-band nature provides two sets of Andreev bound states which carry two supercurrents with different amplitudes. When the magnetization direction of the ferromagnet is suitably chosen, two supercurrents experience opposite phase shifts from the conventional sinusoidal current-phase relation. Then the total Josephson current results in a continuously tunable ground-state phase difference by adjusting the ferromagnet parameters and the triplet-singlet ratio of noncentrosymmetric superconductors. The physics picture and analytical results are given on the basis of the $s$+$p$ wave, while the numerical results are reported on both $s$+$p$ and $d$+$p$ waves. For the $d$+$p$ wave, we find novel states in which the supercurrents are totally carried by continuous propagating states instead of discrete Andreev bound states. Instead of carrying supercurrent, the Andreev bound states which here only appear above the Fermi energy block the supercurrent flowing along the opposite direction. These novel states advance the understaning of the relation between Andreev bound states and the Josephson current. And the ground-state phase difference serves as a tool to determine the triplet-singlet ratio of noncentrosymmetric superconductors.