Interlayer coupling of valley and layer in the homostructure bilayer ScI₂

Despite transformative progress in valleytronic manipulation <i>via</i> 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 <i>via</i> 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.