Nonconventional screening of Coulomb interaction in two-dimensional semiconductors and metals: A comprehensive cRPA study of MX2 (M=Mo, W, Nb, Ta; X=S, Se, Te)

Experimental observations of large exciton binding energies and non-hydrogenic Rydberg series in 2D semiconducting TMDs, along with deviations in plasmon dispersion in 2D metallic TMDs, suggest the presence of a nonconventional screening of the Coulomb interaction. The experimentally observed Mott insulating state in the charge density wave (CDW) reconstructed lattice of TMDs containing 4d and 5d elements further confirms the presence of strong Coulomb interactions in these systems. In this study, we use first-principles electronic structure calculations and constrained random-phase approximation to calculate the Coulomb interaction parameters (partially screened U and fully screened W) between localized d electrons in 2D TMDs. We specifically explore materials represented by the formula MX2 (M=Nb, Ta, Mo, W, and X=S, Se, Te) and consider three different phases (1H, 1T, and 1T'). Our results show that the short-range interactions are strongly screened in all three phases, whereas the long-range interactions remain significant even in metallic systems. This nonconventional screening provides a compelling explanation for the deviations observed in the usual hydrogenic Rydberg series and conventional plasmon dispersion in 2D semiconducting and metallic TMDs, respectively. Our calculations yield on-site Coulomb interaction parameters U within the ranges of 0.8-2.5 eV, 0.8-1.9 eV, and 0.9-2.4 eV for the 1H, 1T, and 1T' structures, respectively. Furthermore, our findings indicate a substantially high ratio of on-site effective Coulomb interaction to bandwidth (U_eff/W_b >> 1) in CDW TMDs, providing robust evidence for the experimentally observed strongly correlated Mott phase.