Small Organic Molecule-Catalyzed Synthesis of a Van der Waals Flat-band Superconductor

Van der Waals (vdW) layered materials provide an exciting platform to explore structure-property relationships due to their high tunability in multiple dimensions. Novel vdW materials offer opportunities to study emerging quantum phenomena, particularly as they approach the two-dimensional limit. Moreover, the vdW gaps can host foreign species that modify the properties of the inorganic host layers through charge transfer or host-guest interactions. In this study, we present a small organic molecule-catalyzed synthesis method that converts a small-gap vdW semiconductor into an all-inorganic vdW superconductor with a transition temperature of 3.8 K. This vdW superconductor can be exfoliated into ultrathin flakes while maintaining its superconducting properties. Specifically, we uncovered the reaction mechanism through a combination of advanced chemical characterization techniques and transport measurements, emphasizing its role in the discovery of this new vdW superconductor. Additionally, angle-resolved photoemission spectroscopy (ARPES) reveals that this superconductor features a flat band close to the Fermi surface.