Periodic Structure Formed by Atomic-Disordered Lamellar Building Blocks Enables Two-Dimensional Superconductivity in SiP ₂

The discovery of quasicrystals and ordered amorphous carbon clusters significantly expands our understanding of the static topological order in solids that goes beyond crystalline and amorphous phases. However, our knowledge of unconventional structures constructed from various disordered building blocks remains extremely limited. Here, we report the successful construction of an ordered-stacking amorphous layer structure in SiP₂ from its pristine crystal form using the high-pressure method, which was robustly validated through scanning transmission electron microscopy and X-ray diffraction analyses. Remarkably, typical two-dimensional superconductivity was found in the unique structure of SiP₂ bulks, as evidenced by the Berezinskii-Kosterlitz-Thouless transition and anisotropic upper critical field measurements. Theoretical calculations reveal that the mutual repulsion of the lone-pair electrons on the phosphorus atoms exposed between the SiP₂ layers hinders the interlayer bonding, stabilizing the layered stacking structure and enabling 2D superconductivity under high pressure. This work introduces an unrevealed solid-state category with exotic properties according to the degree of static topological order.