dc Josephson Effect in Altermagnets

The ability of magnetic materials to modify superconductors is an active research area for possible applications in thermoelectricity, quantum sensing, and spintronics. We consider the fundamental properties of the Josephson effect in a class of magnetic materials that recently have attracted much attention: altermagnets. We show that despite having no net magnetization and a band structure qualitatively different from ferromagnets and from conventional antiferromagnets without spin-split bands, altermagnets induce 0-π oscillations. The decay length and oscillation period of the Josephson coupling are qualitatively different from ferromagnetic junctions and depend on the crystallographic orientation of the altermagnet. The Josephson effect in altermagnets thus serves a dual purpose: it acts as a signature that distinguishes altermagnetism from ferromagnetism and conventional antiferromagnetism and offers a way to control the supercurrent via flow direction anisotropy.