Quasihydrostatic versus nonhydrostatic pressure effects on the electrical properties of NiPS3

We report combined x-ray diffraction (XRD) and electrical transport studies of the van der Waals (vdW) insulator NiPS3 to elucidate a pressure-induced insulator-to-metal transition (IMT). On application of quasihydrostatic pressure, two successive structural transitions occur at 10 and 29.4 GPa, as evidenced by the XRD and resistivity measurements. The concomitant IMT with a monoclinic-to-trigonal structural transition near 29.4 GPa turns out to be a common feature of the MPS3 family (M=transition metals). Under uniaxial-like pressure, the critical pressure for IMT is drastically reduced to P=12.5 GPa. These results showcase that the IMT is susceptible to strain and hydrostatic environments and that pressure offers a new venue to control a dimensional crossover in layered vdW materials.