Metal-insulator transition inNiS2−xSexand the local impurity self-consistent approximation model

Angle-resolved photoemission spectroscopy (ARPES) measurements on ${\mathrm{NiS}}_{2-x}{\mathrm{Se}}_x$ single crystals show the evolution of a narrow band near the Fermi level, which develops in the vicinity of the correlation-driven metal-insulator transition. To model the metal-insulator transition, we use a two-band Hubbard model, which has been studied extensively to describe transition-metal compounds, and use a dynamical mean-field-theory approach. The ARPES data are in striking qualitative agreement with the predictions of the model. Comparison of our data to the calculations suggests a possible mechanism for the metal-insulator transition with Se substitution in which both charge-transfer and hole-doping effects are present.