Mott metal-insulator transitions in pressurized layered trichalcogenides

TL;DR

This study investigates pressure-induced Mott metal-insulator transitions in layered transition metal phosphorous trichalcogenides, revealing distinct structural responses linked to orbital degrees of freedom, with implications for ultrafast electronic switching.

Contribution

It provides the first detailed ab-initio analysis of Mott transitions in $M{ m P}X_3$ compounds, highlighting the role of orbital types in structural and electronic phase changes.

Findings

MnPS$_3$ undergoes an isosymmetric structural transition with Mn-Mn dimer formation.

NiPS$_3$ and NiPSe$_3$ exhibit bandwidth-controlled Mott transitions without structural change.

Ni-based compounds are promising for ultrafast resistivity switching applications.

Abstract

Transition metal phosphorous trichalcogenides, $M{\rm P}X_3$ ($M$ and $X$ being transition metal and chalcogen elements respectively), have been the focus of substantial interest recently because of their possible magnetism in the two-dimensional limit. Here we investigate material properties of the compounds with $M$ = Mn and Ni employing $\textit{ab-initio}$ density functional and dynamical mean-field calculations, especially their electronic behavior under external pressure in the paramagnetic phase. Mott metal-insulator transitions (MIT) are found to be a common feature for both compounds, but their lattice structures show drastically different behaviors depending on the relevant orbital degrees of freedom, i.e. $t_{\rm 2g}$ or $e_{g}$. MnPS$_3$ undergoes an isosymmetric structural transition by forming Mn-Mn dimers due to the strong direct overlap between the neighboring $t_{\rm 2g}$ orbitals, accompanied by a significant volume collapse and a spin-state transition. In contrast, NiPS$_3$ and NiPSe$_3$, with their active $e_g$ orbital degrees of freedom, do not show a structural change at the MIT pressure or deep in the metallic phase. Hence NiPS$_3$ and NiPSe$_3$ become rare examples of materials hosting electronic bandwidth-controlled Mott MITs, thus showing promise for ultrafast resistivity switching behavior.