Interlayer coupling of valley and layer in the homostructure bilayer ScI₂

Despite transformative progress in valleytronic manipulation via heterostructure engineering, the valley-layer coupling mechanisms in homostructure two-dimensional (2D) systems remain a fundamental challenge. Here, we construct a homostructure bilayer ScI₂ and find that it exhibits both ferroelectricity and ferrovalley properties, with its valley polarization tunable via interlayer sliding symmetry. Interlayer sliding from AB to AC stacking requires only 14.7 meV energy, yet drives an appreciable 114 meV valley polarization alongside robust out-of-plane ferroelectric polarization reaching 3 × 10^-11 C m^-1. Specially, the Curie temperature of bilayer ScI₂ reaches up to 615 K, making it favorable for applications at room temperature. Also, the valley-layer interplay in the ScI₂ homostructure drives a layer-locked anomalous Hall effect with electrically switchable polarization. The coupled valley and layer degrees of freedom in ScI₂ bilayers establish a sliding symmetry-protected mechanism for valley polarization materials in homostructures.