Triferroic Material and Electrical Control of Valley Degree of Freedom

The generation and manipulation of valley polarization in controllable ways are important for the valley-related physics and devices. In analogy to multiferroic materials with more than one ferromagnetic, ferroelectric, and ferroelastic orders, a new triferroic system with ferromagnetism, ferroelectricity, and ferrovalley is proposed, namely, the monolayer AgBiP₂Se₆/CrI₃ van der Waals heterostructure. Using density functional theory, we further predict that the electrical control on the valley degree of freedom could be realized in this triferroic system. The mechanism of electrically controlled valley is elucidated as an intermediate coupling between lattice and ferroelectricity. The coupling of three ferroic orders in triferroic material paves the way for electrically controlled valleytronic devices.