Stacking engineering of heterostructures of WS2 homolayers

Stacking engineering provides an effective route for tailoring ferroelectric properties and electronic band structures in two-dimensional materials, thereby enabling controllable modulation of their optical responses. With the successful experimental realization of bilayer R-phase single-crystalline WS2, the fabrication of multilayer TMD heterostructures with different stacking has become feasible. However, how complex stacking sequences cooperatively regulate the intrinsic properties of such systems remains poorly understood. To address this issue, we employ first-principles calculations to systematically construct and investigate four-layer WS2 heterostructures with different H/R stacking sequences. R-stacking breaks inversion symmetry and induces out-of-plane polarization; in homostructures composed of mixed R- and H-stacking sequences, the net polarization is governed by the number and relative orientation of the R-stacked bilayers. Spin-projected band analyses indicate that spin-valley locking is preserved across all stacking configurations and spin orientation at K valley is primarily governed by the global stacking symmetry. Layer-projected results further reveal that the relative contributions of different layers to the K-valley band-edge states depend sensitively on the stacking configuration, indicating stacking-dependent interlayer coupling effects. In addition, GW-BSE calculations capture pronounced excitonic features in the optical absorption spectra of different stacking configurations. These results establish a unified picture linking interlayer sliding, ferroelectricity, electronic structure, and optical response, highlighting stacking engineering as an effective strategy for designing reconfigurable two-dimensional ferroelectric and valleytronic devices.