Pressure-Induced Superconductivity at 15 K in van-der-Waals Ferroelectric CuInP ₂ S ₆

Van der Waals layered transition metal thiophosphate CuInP 2 S 6 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 CuInP 2 S 6 . 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 (MPX 3 ) family. We attribute the origin of this high T c in CuInP 2 S 6 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 MPX 3 materials and highlight pressure as a powerful tool for exploring high- T c superconductivity in sulfur-based systems.