Orbital-selective Peierls phase in the metallic dimerized chain MoOCl2

Abstract

Using ab initio density functional theory, here we systematically study the monolayer ${\mathrm{MoOCl}}_{2}$ with a $4{d}^{2}$ electronic configuration. Our main result is that an orbital-selective Peierls phase (OSPP) develops in ${\mathrm{MoOCl}}_{2}$, 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 ${\mathrm{MoOCl}}_{2}$ 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 $3{d}^{2}$ configuration, as in ${\mathrm{CrOCl}}_{2}$.