$d$-wave Surface Altermagnetism in Centrosymmetric Collinear Antiferromagnets

TL;DR

This paper reveals the symmetry conditions necessary for surface altermagnetism in centrosymmetric collinear antiferromagnets, demonstrating how specific surface symmetries enable nonrelativistic d-wave spin splitting.

Contribution

It identifies the symmetry criteria for surface altermagnetism and illustrates this mechanism through first-principles calculations on specific antiferromagnetic materials.

Findings

Surface altermagnetism requires breaking certain antiunitary symmetries.

The mechanism is demonstrated in V3Al and BaMn2Sb2, but not in MnPt.

The effect persists despite spin-orbit coupling, with some reduction in heavier elements.

Abstract

Broken inversion symmetry at the surfaces of centrosymmetric collinear antiferromagnets lifts combined inversion and time-reversal symmetry ($PT$) and can, in principle, enable nonrelativistic d-wave spin splitting, termed surface altermagnetism. Combining symmetry analysis with first-principles calculations, we show that surface inversion breaking, while necessary, is not sufficient for this effect. Surface altermagnetism emerges only when no antiunitary symmetry survives at the surface that exchanges the two antiferromagnetically coupled surface sublattices and enforces spin degeneracy. We demonstrate this mechanism explicitly for the centrosymmetric G-type antiferromagnets V$_3$Al and BaMn$_2$Sb$_2$, and contrast it with MnPt, where a sublattice-exchanging symmetry survives at the surface in the form of translation-time-reversal symmetry ($tT$), thereby preserving spin degeneracy despite broken inversion symmetry. The mechanism is shown to apply across multiple classes of centrosymmetric antiferromagnets and remains robust against spin-orbit coupling, although relativistic spin mixing in heavier-element compounds may reduce the observable spin polarization. These results establish a symmetry-based route toward realizing robust nonrelativistic momentum-dependent spin polarization at antiferromagnetic surfaces and interfaces.