d -wave surface altermagnetism in centrosymmetric collinear antiferromagnets

Broken inversion symmetry at the surfaces of centrosymmetric collinear antiferromagnets lifts the combined inversion and time-reversal symmetry ( P T ) and can enable nonrelativistic d -wave spin splitting, termed surface altermagnetism. Combining symmetry analysis with first-principles calculations, we show that inversion breaking alone is necessary but not sufficient for this effect. Instead, surface altermagnetism emerges only when no degeneracy-protecting symmetry survives at the surface that exchanges the two antiferromagnetically coupled sublattices. We demonstrate this mechanism for the G -type antiferromagnets V 3 Al and BaMn 2 Sb 2 , and contrast it with MnPt, where the translation–time-reversal symmetry ( t T ) survives at the surface and preserves spin degeneracy despite broken inversion symmetry. We further show that the mechanism applies 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.