Strain-Switchable Piezovalley States in Janus Altermagnetic V2AsHO

Altermagnets enable momentum-dependent spin splitting without net magnetization, but coupling such spin-split electronic states to switchable valley and electromechanical degrees of freedom remains largely unexplored. Here, using first-principles calculations, we identify Janus monolayer V2AsHO as a two-dimensional altermagnetic semiconductor hosting strain-switchable piezovalley states. The compensated antiferromagnetic ground state exhibits pronounced momentum-dependent spin splitting, consistent with altermagnetic order. Owing to the broken out-of-plane mirror symmetry of the Janus lattice, V2AsHO possesses a finite out-of-plane piezoelectric response. More importantly, uniaxial strain lifts the degeneracy between the X and Y valleys and reversibly switches the valley polarization, whereas biaxial strain largely preserves their equivalence. Carrier doping under uniaxial strain further induces a piezomagnetic response, linking the strain-induced valley imbalance to magneto-electromechanical functionality. Polarization-dependent optical absorption exhibits a strain-dependent anisotropy correlated with the piezovalley state.