  The van der Waals (vdW) semiconductor black phosphorus has been widely
studied, especially after the discovery of phosphorene. On the contrary, its
sister compound violet phosphorus, also a vdW semiconductor, has been rarely
studied. Here we report the pressure-induced superconductivity in violet
phosphorus up to $\sim$40 GPa. The superconductivity emerges at 2.75 GPa, which
is well below the structural transition from monoclinic ($M$) to rhombohedral
($R$) structure at 8.5 GPa. The superconducting transition temperature
($T$$\rm_c$) shows a plateau of $\sim$7 K from 3.6 to 15 GPa, across the $M$ to
$R$ structural transition, then jumps to another plateau of $\sim$10 K in the
simple cubic ($C$) structure above 15 GPa. The temperature-pressure
superconducting phase diagram of violet phosphorus is established, which is
different from that of black phosphorus at low pressure. For black phosphorus,
the superconductivity emerges until the structural transition from orthorhombic
($O$) to $R$ structure at $\sim$5 GPa, with a lower $T$$\rm_c$ than violet
phosphorus. The pressure-induced superconductivity in violet phosphorus
demonstrates its tunable electronic properties, and more electronics and
optoelectronic applications are expected from this stable vdW semiconductor at
ambient conditions.
