Influence of dimensionality on superconductivity in pressurized 3D SnPSe3 single crystal

Metal phosphorus trichalcogenides (MPX3) constitute a vast family of van der Waals materials, comprising more than four dozen candidates with versatile properties spanning spin crossover, catalysis, and pressure-induced superconductivity. While exceptions exist, such as SnPSe3, which adopts both 2D and 3D crystalline structures, with its 2D isomer recently exhibiting superconductivity under high pressure, the investigation of its 3D counterpart presents an intriguing opportunity to explore the dimensional influence on superconductivity. Here, we present detailed high-pressure measurements of bulk SnPSe3, integrating electrical transport measurements, synchrotron diffraction, and theoretical structure predictions. Our findings reveal a monoclinic (P21/c, No. 14) to orthorhombic (Cmcm, No. 63) phase transition in SnPSe3 at P=22GPa, which remains crystalline to 50.5 GPa. Concurrent with this structural change, SnPSe3 undergoes a semiconductor-superconductor transition at 18.9 GPa. Furthermore, as pressure increases, the transition temperature (Tc) monotonically rises to 6.9 K at 85.6 GPa. This behavior sharply contrasts with that of reported 2D SnPSe3, where a relatively higher Tc is achieved accompanied with amorphization at around 30 GPa. The notable difference in structural stability and superconductivity thus renders SnPSe3 a clean and ideal platform for exploring additional unforeseen dimensional effects.