Spin-dependent quasiparticle reflection and bound states at interfaces with itinerant antiferromagnets

TL;DR

This paper develops a quasiclassical theory for interfaces between itinerant antiferromagnets and superconductors, revealing spin-dependent quasiparticle reflection and zero-energy bound states that influence supercurrent behavior.

Contribution

It introduces a novel quasiclassical framework for AF/superconductor interfaces, uncovering spin-dependent retroreflection and bound states not previously described.

Findings

Spin-dependent retroreflection occurs at AF/N interfaces.

Zero-energy bound states form at AF/sSC interfaces with a pi phase difference.

Bound states are split in AF/sSC junctions and carry supercurrent.

Abstract

We present a formulation of the quasiclassical theory of junctions between itinerant antiferromagnets (AF) and s-wave (sSC) and d-wave superconductors (dSC). For the simplest two-sublattice antiferromagnet on a bipartite lattice, we derive Andreev-type equations and show that their solutions lead to a novel channel of quasiparticle reflection. In particular, quasiparticles in a normal metal with energies less than or comparable to the antiferromagnetic gap experience spin-dependent retroreflection at antiferromagnet-normal metal (AF/N) transparent (100) and (110) interfaces. A relative phase difference of pi between up spin and down spin quasiparticle reflection amplitudes is shown to lead to zero-energy interface bound states on AF/sSC interfaces. For an sSC/AF/sSC junction, these bound states are found to be split, due to a finite width of the AF interlayer, and carry the supercurrent. At AF/dSC interfaces we find no zero-energy bound states for both interface orientations we considered, in contrast with the case of (110) impenetrable surface of a dSC.