Sliding-induced ferrovalley polarization and possible antiferromagnetic half-metal in bilayer altermagnets

Abstract: Altermagnets, a newly discovered class of materials, exhibit zero net magnetization while hosting spin-split electronic bands. However, monolayer altermagnets maintain degenerate band gaps at the high-symmetry X and Y points in the Brillouin zone, manifesting a paravalley phase characterized by unpolarized valley states. In this work, we demonstrate that spontaneously broken valley degeneracy can be achieved through interlayer sliding in engineered M$_2$A$_2$B and M$_2$AA$'$B bilayer altermagnets by first-principles calculations and minimal microscopic model. We propose a promising route to achieve antiferromagnetic half-metal driven by sliding and emergent ferrovalley phase without applied electric field, which is realized in the V$_2$SSeO engineered bilayer. Our calculations also reveal that Mo$_2$O$_2$O exhibits the largest valley splitting gap of ~0.31 eV, making it a promising candidate for valley-spin valve devices. Furthermore, band structure calculations on Mo$_2$AA$'$O materials demonstrate that increasing the difference in atomic number ($\Delta$Z) between A and A$'$ site atoms effectively enhances valley polarization. This work establishes a novel platform for discovering and controlling ferrovalley states in altermagnetic systems.