Spin-Josephson effect in antiferromagnetic tunnel junctions

TL;DR

This paper predicts a Josephson-like effect for antiferromagnetic tunnel junctions, where a staggered magnetization current arises from coherent tunneling of particle-hole pairs, extending the concept of Josephson effects beyond superconductors.

Contribution

It introduces a theoretical model predicting a Josephson-like effect in antiferromagnetic junctions, highlighting the role of coherent spin-one charge-zero particle-hole pairs.

Findings

Equilibrium staggered magnetization current proportional to conductance and cross product of magnetizations.

Current arises from coherent tunneling of particle-hole pairs with antiferromagnetic wave vector.

Comparison with standard Josephson effects reveals both similarities and differences.

Abstract

In the Josephson effect, coherent Cooper pair tunneling is driven by the phase difference between the superconducting order parameters on opposite sides of the junction. By analogy, differences in order parameters across a junction should lead to coherent tunneling of the condensed objects that exist in the broken symmetry state. To exhibit the generality of this phenomenon and make predictions from a realistic model, we study the case of a tunnel junction between two itinerant antiferromagnets. At the mean-field level, we find an equilibrium current of the staggered magnetization through the junction that is proportional the normal state conductance and to $\mathbf{S}_{L}\times \mathbf{S}_{R}$ where $\mathbf{S}_{L}$ and $\mathbf{S}_{R}$ are the staggered magnetizations on either sides. Microscopically, this effect comes from coherent tunneling of spin-one charge-zero particle-hole pairs that have a net wave vector equal to the antiferromagnetic one. We explain similarities and differences with the standard DC and AC Josephson effects.