Strain-induced valley polarization, topological states, and piezomagnetism in two-dimensional altermagnetic V2Te2O, V2STeO, V2SSeO, and V2S2O

Altermagnets (AM) are a recently discovered third class of collinear magnets and have been attracting significant interest in the field of condensed matter physics. Here, based on first-principles calculations and theoretical analysis, we propose four two-dimensional (2D) magnetic materials-monolayers V2Te2O, V2STeO, V2SSeO, and V2S2O-as candidates for altermagnetic materials. We show that these materials are semiconductors with spin-splitting in their nonrelativistic band structures. Furthermore, in the band structure, there is a pair of Dirac-type valleys located at the time-reversal invariant momenta (TRIM) X and Y points. These two valleys are connected by crystal symmetry instead of time-reversal symmetry. We investigate the strain effect on the band structure and find that uniaxial strain can induce valley polarization, topological states in these monolayer materials. Moreover, piezomagnetism can be realized upon finite doping. Our result reveals interesting valley physics in monolayers V2Te2O, V2STeO, V2SSeO, and V2S2O, suggesting their great potential for valleytronics, spintronics, and multifunctional nanoelectronics applications.