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

The layered metal phosphorous trisulfide FePS3 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 FePS3 using first-principles methods based on density functional theory and embedded dynamical mean field theory. We find that the Mott transition in FePS3 can be orbital selective, with t2g states undergoing a correlation-induced insulator-to-metal transition while eg 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 FePS3 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 (≤18 GPa).