Topological superconductivity in altermagnet-superconductor heterostructures

Altermagnets are a class of materials that possess a unique combination of magnetic and spatial symmetries. Despite having zero net magnetic moment due to fully compensated antiferromagnetic order, the hallmark feature of an altermagnet is nonrelativistic spin splitting in the electronic bands??"a characteristic typically associated with ferromagnets. While their band structures are theoretically well understood, altermagnetic fluctuations and the formation of the corresponding instabilities remain largely unexplored. We establish a correspondence between the quantum metric in the normal phase and the altermagnetic spin splitting of the ordered phase, and show that the quantum metric favors altermagnetism.

Further, we show that altermagnets naturally tend toward p-wave superconductivity, and show how it can be induced by proximitizing an altermagnet with a conventional superconductor. We propose a heterostructure that interfaces altermagnetic monolayer V2Se2O with a conventional s-wave superconductor. Starting from an ab-initio description of V2Se2O, we construct a low-energy model of its spin-split Fermi surface and study the superconducting instability of the coupled stack. We find that the momentum-dependent exchange splitting of the altermagnet strongly favors equal-spin pairing and converts the proximity-induced order into a fully gapped p-wave state. Over a broad range of interface parameters, the resulting Bogoliubov??"de Gennes bands carry a nonzero Chern number, and slab spectra exhibit chiral Majorana edge modes traversing the bulk gap. We further quantify the inverse proximity effect and show how the induced gap evolves across a finite multilayer stack, providing practical guidance for interface fabrication and experimental detection.

Lastly, we discuss how superconducting altermagnets can be used to generate and transport persistent, spin-polarized supercurrents, which we dub “spin-current dynamo effect”.

Speaker: Niclas Heinsdorf, Max Planck Graduate Center for Quantum Materials