Superconducting Junctions with Ferromagnetic, Antiferromagnetic or Charge-Density-Wave Interlayers

TL;DR

This paper theoretically investigates the spectra and spin structures of Andreev states and Josephson currents in superconducting junctions with ferromagnetic, antiferromagnetic, or charge-density-wave interlayers, revealing novel reflection channels and bound state behaviors.

Contribution

It introduces a new quasiclassical approach to analyze interfaces involving itinerant antiferromagnets and uncovers novel quasiparticle reflection mechanisms affecting Andreev states.

Findings

Josephson current exhibits nonmonotonic dependence on misorientation angle.

Novel Q reflection channel dominates in AF/SC interfaces, creating near-zero energy Andreev states.

Bound states split and carry supercurrent in AF/SC/AF junctions.

Abstract

Spectra and spin structures of Andreev interface states and the Josephson current are investigated theoretically in junctions between clean superconductors (SC) with ordered interlayers. The Josephson current through the ferromagnet-insulator-ferromagnet interlayer can exhibit a nonmonotonic dependence on the misorientation angle. The characteristic behavior takes place if the pi state is the equilibrium state of the junction in the particular case of parallel magnetizations. We find a novel channel of quasiparticle reflection (Q reflection) from the simplest two-sublattice antiferromagnet (AF) on a bipartite lattice. As a combined effect of Andreev and Q reflections, Andreev states arise at the AF/SC interface. When the Q reflection dominates the specular one, Andreev bound states have almost zero energy on AF/ s-wave SC interfaces, whereas they lie near the edge of the continuous spectrum for AF/d-wave SC boundaries. For an s-wave SC/AF/s-wave SC junction, the bound states are found to split and carry the supercurrent. Our analytical results are based on a novel quasiclassical approach, which applies to interfaces involving itinerant antiferromagnets. Similar effects can take place on interfaces of superconductors with charge density wave materials (CDW), including the possible d-density wave state (DDW) of the cuprates.