Altermagnetism, piezovalley, and ferroelectricity in two-dimensional Cr2SeO altermagnet

The study on altermagnet is receiving extensive research efforts due to its directional-dependent spin-polarized band structure. Here, we investigate the multifunctional properties of the Janus Cr2SeO monolayer system. The Cr2SeO monolayer exhibits an in-plane magnetic anisotropy energy of -0.28 meV/cell and a Neel temperature of around 280 K, which is further enhanced to 315 K under 1% uniaxial compressive strain. The Janus Cr2SeO exhibits spin band inversion with a large spin splitting of 0.38 eV at the Y and X high-symmetry points. Nonetheless, the valleys are degenerated due to the diagonal mirror symmetry. The uniaxial strain effectively breaks the diagonal mirror symmetry in the Janus Cr2SeO monolayer, and the strain-induced valley polarization of up to 90 meV is achieved. Furthermore, the uniaxial strain tunes the band gap between 0.30 eV to 0.76 eV. Moreover, Cr2SeO demonstrates ferroelectricity, with a total electric polarization of 5.34 pC/m, which increases to 5.52 pC/m under small uniaxial strain. Besides, we found a large vertical piezoelectric coefficient d31 of 1.18 pm/V. Our study suggests that the Janus Cr2SeO is a promising platform for Valleytronics and ferroelectric memory applications at room temperature.