Monolayer Ru(OLi)₂ as an Ideal Room-Temperature Ferrovalley Semiconductor with Intrinsic Out-of-Plane Ferromagnetism

Achieving sizable valley polarization in room-temperature ferrovalley semiconductors with out-of-plane magnetization is of great significance for fundamental physics and information technology. Using ab initio calculations and Monte Carlo simulations, we identify the freestanding Ru(OLi)2 monolayer as a scarce Ising-type semiconducting ferromagnet with an ultrahigh Curie temperature of 1121 K and a considerable perpendicular magnetic anisotropy energy of 1212 μeV per unit cell. Due to its out-of-plane ferromagnetism and spin–orbital coupling effect, the inversion-symmetry-broken Ru(OLi)2 monolayer holds a spontaneous ultraclean valley polarization up to 220 meV in the top valence band. Also, we validate such a significant valley polarization by the perturbation theory from the orbital projection band structure. Local direct bandgaps at two inequivalent valley states render selective excitation of spin and valley-coupled carriers realizable through optical fields of different visible frequencies. The valley-contrasting Berry curvature facilitates the observation of an anomalous valley Hall effect in the experimentally feasible hole-doped regime. These exceptional merits, along with their intrinsic robustness against a moderate range of equibiaxial strains, shed light on the bright application prospect of the synthesizable Ru(OLi)2 monolayer for valley-based spintronic and optoelectronic devices at room temperature.