Pressure-induced superconductivity in the van der Waals semiconductor violet phosphorus

The van der Waals (vdW) semiconductor black phosphorus (BP) has been extensively studied, especially since the discovery of phosphorene. In contrast, its sister compound violet phosphorus (VP), another vdW semiconductor, has received far less attention. Here we report the pressure-induced superconductivity in VP up to $\ensuremath{\sim}40$ GPa. The zero-resistance superconducting transition emerges at 3.57 GPa, due to a structural phase transition from monoclinic $(M)$ to rhombohedral $(R)$ structure. The superconducting transition temperature $({T}_{\mathrm{c}})$ shows a plateau of $\ensuremath{\sim}7$ K from 3.6--15 GPa in the $R$ structure, then jumps to another plateau of $\ensuremath{\sim}10$ K above 15 GPa in the simple cubic $(C)$ structure. We establish and compare the temperature-pressure superconducting phase diagram of VP with that of BP. For BP, the superconductivity appears with an orthorhombic $(O)\text{\ensuremath{-}}R$ structural transition at a critical pressure of 5 GPa, with a lower ${T}_{\mathrm{c}}$ than VP. The pressure-induced structural phase transition and superconductivity in VP demonstrate its pressure-sensitive and easily tunable electronic properties. These properties suggest promising prospects for further electronic and optoelectronic applications, particularly given its stability as a vdW semiconductor at ambient conditions.