Pressure induced insulator-to-metal transition in few-layer FePS₃ at 1.5 GPa

In two-dimensional (2D) van der Waals (vdW) layered materials the application of pressure often induces a giant lattice collapse, which can subsequently drive an associated Mott transition. Here, we investigate room-temperature layer-dependent insulator-metal transition (IMT) and probable spin-crossover (SCO) in vdW magnet, FePS$_3$, under high-pressure using micro-Raman scattering. Experimentally obtained spectra, in agreement with the computed Raman modes, indicate evidence of IMT of FePS$_3$ started with a thickness-dependent critical pressure ($P_c$) which reduces to 1.5 GPa in trilayer flakes compared to 10.8 GPa for the bulk counterpart. Using a phenomenological model, we argue that strong structural anisotropy in few-layer flakes enhances the in-plane strain under applied pressure and is, therefore, ultimately responsible for reducing the critical pressure for the IMT with decreasing layer numbers. Reduction of the critical pressure for phase transition in vdW magnets to 1-2 GPa marks the possibility of using intercalated few-layers in the field-effect transistor device architecture, and thereby, avoiding the conventional use of the diamond anvil cell (DAC).