Josephson Effect due to Odd-frequency Pairs in Diffusive Half Metals

TL;DR

This paper investigates how odd-frequency spin-triplet Cooper pairs enable the Josephson effect in superconductor/half-metal/superconductor junctions, revealing experimental signatures like a peak in local density of states.

Contribution

It demonstrates that spin-flip scattering at interfaces induces odd-frequency triplet pairing, facilitating the Josephson effect in half metals, which was not previously established.

Findings

Spin-flip scattering enables Josephson current via odd-frequency pairs.

Large zero-energy peak in local density of states in half metals.

Detection of odd-frequency pairs via scanning tunneling spectroscopy.

Abstract

The Josephson effect in superconductor / diffusive ferromagnet / superconductor (SFS) junctions is studied using the recursive Green function method in the regime of large exchange energy in a ferromagnet. Motivated by recent experiment [R. S. Keizer, et. al., Nature 439, 825 (2006)] we also address the case of superconductor / diffusive half metal / superconductor junctions. The pairing function in spin-singlet and triplet channels, the Josephson current and their mesoscopic fluctuations are calculated. We show that the spin-flip scattering at the junction interfaces opens the Josephson channel of the odd-frequency spin-triplet Cooper pairs. As a consequence, the local density of states in half metals has a large peak at the Fermi energy. Therefore odd-frequency pairs can be detected experimentally by using the scanning tunneling spectroscopy.