Orbital-selective Peierls phase in the metallic dimerized chain MoOCl$_2$

TL;DR

This study reveals an orbital-selective Peierls phase in monolayer MoOCl$_2$, where specific orbitals form localized dimers while others remain itinerant, leading to a metallic state with orbital-dependent properties.

Contribution

It demonstrates the existence of an orbital-selective Peierls phase in MoOCl$_2$, combining ab initio calculations with analysis of orbital-dependent dimerization and metallic behavior.

Findings

MoOCl$_2$ exhibits orbital-selective dimerization of Mo-$d_{xy}$ orbitals.

The material remains globally metallic despite orbital-specific bonding.

The Peierls distortion induces a gap in localized orbitals while itinerant orbitals sustain conductivity.

Abstract

Using {\it ab initio} density functional theory, here we systematically study the monolayer MoOCl$_2$ with a $4d^2$ electronic configuration. Our main results is that an orbital-selective Peierls phase (OSPP) develops in MoOCl$_2$, resulting in the dimerization of the Mo chain along the $b$-axis. Specifically, the Mo-$d_{xy}$ orbitals form robust molecular-orbital states inducing localized $d_{xy}$ singlet dimers, while the Mo-$d_{xz/yz}$ orbitals remain delocalized and itinerant. Our study shows that MoOCl$_2$ is globally metallic, with the Mo-$d_{xy}$ orbital bonding-antibonding splittings opening a gap and the Mo-$d_{xz/yz}$ orbitals contributing to the metallic conductivity. Overall, the results resemble the recently much discussed orbital-selective Mott phase but with the localized band induced by a Peierls distortion instead of Hubbard interactions. Finally, we also qualitatively discuss the possibility of OSPP in the $3d^2$ configuration, as in CrOCl$_2$.