Realistic Description of Competing Interactions in Metallic TMDCs

Two-dimensional transition metal dichalcogenides constitute a prominent showplace for competing many-body instabilities such as superconductivity [Frindt: PRL 28, 299 (1972)], charge-density waves [Ugeda et al.: Nat. Phys. 12, 92 (2016)] and magnetism [Ma et al.: ACS Nano 6, 1695 (2012)]. In this study, we show that even though the observed phase diagrams are complex, the underlying mechanisms are captured by a compact unifying theoretical framework. We apply the constrained random-phase approximation (cRPA) [Aryasetiawan et al.: PRB 74, 125106 (2006)] and constrained density-functional perturbation theory (cDFPT) [Nomura, Arita: PRB 92, 245108 (2015)] to the metallic monolayers H-MX₂ with M ∈ {V, Nb, Ta} and X ∈ {S, Se} and summarize the material specifics with a small number of representative Coulomb and electron-phonon interaction parameters. Both cRPA and cDFPT imply a separation of the electrons into a correlated subspace, here an isolated metallic band, and the rest. We find that all relevant physics emerges from interactions within this subspace. Beyond that, the materials can be well described by very similar tight-binding and mass-spring models.