Strain-modulated valley polarization and piezomagnetic effects in altermagnetic Cr2S2

Abstract

Altermagnetism combines the advantages of both ferromagnetic and antiferromagnetic systems, offering unique spin-splitting properties in antiferromagnetic materials. Currently, it is established that valley polarization in altermagnetism remains largely insensitive to spin–orbit coupling and spin. We select monolayer Cr2S2 as a model altermagnetic system to investigate the mechanism through which an external field modulates valley polarization in altermagnetism. This effect arises from breaking the diagonal mirror symmetry Mxy under uniaxial strain, which lifts the degeneracy of the X and Y valleys, inducing significant valley polarization. Crucially, biaxial strain preserves Mxy symmetry and fails to induce polarization. Uniaxial strain simultaneously induces valley polarization and a nearly uniform Zeeman-like field in the reciprocal lattice space, reaching up to 118.39T under 5% uniaxial strain. Moreover, the symmetry breaking in the monolayer Cr2S2 leads to strong piezomagnetic effects, merging piezomagnetic and altermagnetic characteristics in two-dimensional materials.