Harnessing sliding ferroelectricity for layer-polarized spin Hall effect in ZrX2 (X = Cl, Br, I) bilayers

Quantum layertronics investigates the interaction between the layer degree of freedom in 2D van der Waals materials and electron charge or spin, enabling innovative quantum device applications. Using first-principles calculations, sliding ferroelectricity is demonstrated for the ZrX2 (X = Cl, Br, I) bilayers. The moderate electric polarization (0.24–0.5 pC/m) and sliding energy barrier (11–18.8 meV/f.u.) values of ZrX2 bilayers indicate their suitability for low energy cost and high-speed data writing devices based on sliding ferroelectricity. With the effect of spin–orbit coupling, spin splitting occurs at the T-symmetry-connected valleys of the valence band, generating Berry curvature in the ZrX2 bilayer. When combined with sliding ferroelectricity, this effect leads to significant layer polarization with the layer splittings of 19, 23.5, and 46.7 meV for AB-stacked ZrCl2, ZrBr2, and ZrI2 bilayers, respectively. The coupling between out-of-plane ferroelectricity and electronic structure induces a layer-locked Berry curvature, giving rise to the layer-polarized spin Hall effect (LP-SHE) in bilayers. This LP-SHE is intimately linked to sliding ferroelectricity, allowing for reversible control through ferroelectric switching, making it an ideal candidate for 2D spintronic applications.