Supercurrent decay in ballistic magnetic Josephson junctions

TL;DR

This study reveals that supercurrent decay in ballistic magnetic Josephson junctions is an intrinsic effect caused by exchange splitting and mode dispersion, independent of disorder, with implications for material optimization.

Contribution

It combines density functional theory and Bogoliubov-de Gennes modeling to explain supercurrent decay mechanisms in magnetic Josephson junctions, aligning with recent experiments.

Findings

Supercurrent decays exponentially with ferromagnet thickness.

Exchange splitting can gap out carriers, suppressing Andreev reflection.

Mode dispersion leads to loss of phase synchronization among modes.

Abstract

We investigate transport properties of ballistic magnetic Josephson junctions and establish that suppression of supercurrent is an intrinsic property of the junctions, even in absence of disorder. By studying the role of ferromagnet thickness, magnetization, and crystal orientation we show how the supercurrent decays exponentially with thickness and identify two mechanisms responsible for the effect: (i) large exchange splitting may gap out minority or majority carriers leading to the suppression of Andreev reflection in the junction, (ii) loss of synchronization between different modes due to the significant dispersion of the quasiparticle velocity with the transverse momentum. Our results for Nb/Ni/Nb junctions are in good agreement with recent experimental studies. Our approach combines density functional theory and Bogoliubov-de Gennes model and opens a path for material composition optimization in magnetic Josephson junctions and superconducting magnetic spin valves.