Pressure-Induced Superconductivity at 15 K in van-der-Waals Ferroelectric CuInP₂S₆

Van der Waals layered transition metal thiophosphate CuInP₂S₆ has attracted significant research interest due to its intriguing ferroelectric and optoelectronic properties. In this work, by combining high-pressure Raman spectroscopy, optical absorption measurements, and ab initio calculations, we uncover a cascade of pressure-induced phase transitions in CuInP₂S₆. Remarkably, electrical transport measurements reveal the emergence of superconductivity above 58 GPa. The superconducting transition temperature T_c increases progressively with pressure, reaching 15 K at 215 GPa─the highest T_c reported to date among the metal phosphorus trichalcogenide (MPX₃) family. We attribute the origin of this high T_c in CuInP₂S₆ to a unique pairing mechanism characterized by dynamic carrier exchange between flat bands and highly dispersive bands dominated by sulfur vibrations. Our findings enrich the understanding of layered MPX₃ materials and highlight pressure as a powerful tool for exploring high-T_c superconductivity in sulfur-based systems.