Ferrovalley and topological phase transition behavior in monolayer Ru(OH)2

Abstract

Ferrovalley (FV) materials with outstanding physical properties have garnered significant attention for their potential to revolutionize next-generation electronic devices. Through first-principles calculations, the present study has predicted and identified monolayer Ru(OH)₂ as a promising FV material, which exhibits a large valley polarization of 201 meV and a Curie temperature of up to 306 K. A particularly intriguing aspect of Ru(OH)₂ monolayer is its response to biaxial strain, which leads to fascinating phase transition behavior. Within a range of strains from −3% to 1%, monolayer Ru(OH)₂ maintains its distinctive FV characteristics. However, at a critical tensile strain of 1%, it undergoes a transformation into a half-valley-metal state, showing unique electronic properties. As the strain is further increased, monolayer Ru(OH)₂ manifests a quantum anomalous Hall effect behavior, presenting a topological bandgap of 36 meV. This could surpass the thermal fluctuation at room temperature, thus opening up exciting possibilities for future applications in electronics. Surprisingly, at a critical tensile strain of 2.4%, monolayer Ru(OH)₂ reverts to a half-valley-metal state, and beyond this point, it returns to the FV semiconductor state. The unique properties and versatile phase transitions of monolayer Ru(OH)₂ hold great promise for the development of cutting-edge valleytronic devices.