Orbital-selective Mott phase and non-Fermi liquid in FePS$_3$

TL;DR

This study reveals that FePS$_3$ exhibits an orbital-selective Mott transition under pressure, leading to a non-Fermi liquid state, and demonstrates how pressure can tune its electronic phases between correlated and uncorrelated metals.

Contribution

The paper provides the first theoretical evidence of an orbital-selective Mott phase in FePS$_3$, highlighting pressure-dependent electronic transitions and the emergence of non-Fermi liquid behavior.

Findings

Orbital-selective Mott transition occurs in FePS$_3$ under non-hydrostatic pressure.

The system exhibits a bad metal or non-Fermi liquid state with large fluctuating moments.

Increasing pressure eventually leads to a conventional Fermi liquid state.

Abstract

The layered metal phosphorous trisulfide 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 FePS$_3$ using first-principles methods based on density functional theory and embedded dynamical mean field theory. We find that the Mott transition in 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 non-hydrostatic 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 FePS$_3$ is a novel example of a system that realizes an orbital-selective Mott phase, allowing tuning between correlated and uncorrelated metallic properties in an accessible pressure range ($\leq$ 18 GPa).