Orbital-selective Mott phase and non-Fermi liquid in ${\mathrm{FePS}}_3$

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 ($\le 18$ GPa).

Figure 1

Electronic structures with or without expected structural changes under pressure. The partial densities of states are depicted for (a) HP0-SPD at 0 GPa, (b) HP0-SPD at 10 GPa, (c) HP1-APD at 10 GPa, (d) HP1-APD at 18 GPa, (e) HP2-APC at 10 GPa, and (f) HP2-APC at 18 GPa. Panels (a), (c), and (f) are for stable configurations at the given pressure and are denoted by thicker borders, whereas (b), (d), and (e) are fictitious metastable structures for comparison. The red solid, green dotted, and blue dotted lines correspond to $a_{1g}$, $e_g^{\prime }$, and $e_g$ states, respectively, as denoted in (d). The Fermi level is set to zero.

Figure 2

$k$-resolved spectral functions and PDOS for the three different phases at representative pressure values under the nonhydrostatic pressure condition. $A(k,\omega )$ and the corresponding PDOS are plotted for (a) HP0-SPD (0 GPa), (b) HP1-APD (10 GPa), and (c) HP2-APC (18 GPa).

Figure 3

Imaginary part of self-energy on the imaginary axis. Im $\mathrm{\Sigma }\left(i{\omega }_n\right)$ for HP1-APD (10 GPa) at (a) 300 K and (b) 100 K, and for HP2-APC (18 GPa) at (c) 300 K and (d) 100 K.

Figure 4

Average occupation and spin configurations. (a) Occupation per orbital and (b) probability of spin configurations in HP1-APD (10 GPa) and HP2-APC (18 GPa).

Figure 5

Temperature dependence of resistivity. (a) Resistivity for different temperatures. (b) Im $\mathrm{\Sigma }$ on (left) the imaginary and (right) the real axes.