Orbital-selective Mott phase and non-Fermi liquid in FePS3

The layered metal phosphorous trisulfide ${\mathrm{FePS}}₃$ is reported to be a Mott insulator at ambient conditions and to undergo structural and insulator-metal phase transitions under pressure. However, the character of the resulting metallic states has not been understood clearly so far. Here, we theoretically study the phase transitions of ${\mathrm{FePS}}₃$ using first-principles methods based on density functional theory and embedded dynamical mean field theory. We find that the Mott transition in ${\mathrm{FePS}}₃$ can be orbital selective, with ${t}_2g$ states undergoing a correlation-induced insulator-to-metal transition while ${e}_g$ states remain gapped. We show that this orbital-selective Mott phase, which occurs only when nonhydrostatic pressure is used, is a bad metal (or non-Fermi liquid) with large fluctuating moments due to Hund's coupling. Further application of pressure increases the crystal-field splitting and converts the system to a conventional Fermi liquid with low-spin configurations dominant. Our results show that ${\mathrm{FePS}}₃$ is an example of a system that realizes an orbital-selective Mott phase, allowing tuning between correlated and uncorrelated metallic properties in an accessible pressure range ($\ensuremath{\le}18$ GPa).