Pressure-induced electronic transitions in samarium monochalcogenides

The pressure-induced isostructural insulator-to-metal transition for SmS is characterized by the presence of an intermediate valence state at higher pressure which cannot be captured by density functional theory. As a direct outcome of including the charge and spin fluctuations incorporated in dynamical mean-field theory, we see the emergence of insulating and metallic phases with increasing pressure as a function of changing valence. This is accompanied by significantly improved predictions of the equilibrium lattice constants and bulk moduli for all Sm monochalcogenides verifying experiments. Nudged elastic band analysis reveals the insulating states to have a finite quasiparticle weight, decreasing as the gap closes rendering the transition to be not Mott-like, and classifies these materials as correlated band insulators. The difference between the discontinuous and continuous natures of these transitions can be attributed to the closeness of the sharply resonant Sm-4f peaks to the Fermi level in the predicted metallic states in SmS compared with SmSe and SmTe.