Exchange induced ordinary reflection in a single-channel superconductor-ferromagnet-superconductor junction

TL;DR

This paper investigates how incomplete Andreev reflection at a superconductor-ferromagnet interface affects the quasiparticle spectrum and Josephson current in a ballistic single-channel SFS junction, revealing energy gaps and weak effects on the current.

Contribution

It introduces the impact of incomplete Andreev reflection due to exchange interaction on the spectrum and Josephson effect in a ballistic SFS junction, extending previous models.

Findings

Energy gaps open in the phase-dependent spectrum.

Josephson current is weakly affected by incomplete Andreev reflection.

Significant effects occur only when exchange energy approaches the Fermi energy.

Abstract

The stationnary Josephson effect in a clean Superconductor-Ferromagnet-Superconductor junction is revisited for arbitrarily large spin polarizations. The quasiclassical calculation of the supercurrent assumes that the Andreev reflection is complete for all channels. However, De Jong and Beenakker have shown that the Andreev reflection at a clean FS interface is incomplete, due to the exchange interaction in the ferromagnet. Taking into account this incomplete Andreev reflection, we investigate the quasiparticle spectrum, the Josephson current and the $0-\pi$ transition in a ballistic single channel SFS junction. We find that energy gaps open in the phase dependent spectrum. Although the spectrum is strongly modified when the exchange energy increases, the Josephson current and the $0-\pi$ transition are only weakly affected by the incomplete Andreev reflection, except when the exchange energy is close to the Fermi energy.