Symmetry-breaking-induced valley polarization and pure spin current in altermagnetic Co₂MTe₄ monolayers

Altermagnets combine spontaneous spin splitting with antiferromagnetic coupling, making them a promising platform for spintronic devices. In this work, we demonstrate that the two-dimensional (2D) Co₂MTe₄ (M = Mo, W) monolayers are altermagnetic semiconductors with out-of-plane magnetic easy axes, whose unconventional spin splitting and vanishing net magnetization are protected by combined real-space mirror and spin-space two-fold rotational symmetries. Strain engineering-induced crystal symmetry breaking enables valley polarization and reversal at the X/Y-valley, and subsequently generates a pronounced piezomagnetic response under hole doping. Owing to the valley anisotropy, the Co₂MTe₄ monolayer allows the generation and manipulation of a noncollinear spin current under an in-plane electric field. Notably, a pure spin current analogous to the spin Hall effect can be obtained when the electric field is applied along the bisector of the spin sublattice configuration. These findings reveal strong coupling between spin and valley degrees of freedom and provide an effective route for electric-field control of spin currents.