Mott metal-insulator transitions in pressurized layered trichalcogenides
Abstract
Transition metal phosphorous trichalcogenides, M PX3 (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 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 2g or eg. MnPS3 undergoes an isosymmetric structural transition by forming Mn-Mn dimers due to the strong direct overlap between the neighboring t 2g orbitals, accompanied by a significant volume collapse and a spin-state transition. In contrast, NiPS3 and NiPSe3, with their active eg orbital degrees of freedom, do not show a structural change at the MIT pressure or deep in the metallic phase. Hence NiPS3 and NiPSe3 become rare examples of materials hosting electronic bandwidth-controlled Mott MITs, thus showing promise for ultrafast resistivity switching behavior.