Charge density waves and competition between electron-lattice and spin-lattice couplings in semihydrogenated transition metal dichalcogenides

Abstract

In this work, we apply first-principles calculations to describe the formation of charge density waves in semihydrogenated transition metal dichalcogenides. The effect accompanies structural distortions characterized by triple or double dimerizations in Mo rows. The former, detected in the MoS 2 case as the lowest energy configuration, is a Peiels-like transition induced by the Fermi surface nesting, whereas the latter is metastable and presents a spin-Peierls character, leading to Mo triangles with a frustrated antiferromagnetic configuration. We discuss the phenomenon in terms of a competition between electron-lattice and spin-lattice couplings. We also show that the trend observed in MoS 2 is reversed in the MoSe 2 case, which stabilizes, as the lowest energy configuration, the frustrated antiferromagnetic phase. Other metastable magnetic orderings are described.Our main result is that a TMD monolayer undergoes structural reconstruction upon semihydrogenation induced by two competing instabilities. The first, which predominates in MoS 2 H, is a Peierls-like mechanism driven by electron-lattice couplings. It is characterized by a 2D dimerization in the Mo triangular sublattice (the sulfur sublattices are dragged along), in which Mo dimers are formed along the three Fermi surface nesting directions. The