Electronic structure and the metal-insulator transition inNiS2−xSex

Abstract

We studied the metal-insulator transition in the $\mathrm{Ni}{\mathrm{S}}_{2-x}{\mathrm{Se}}_x$ system in $x=0\mathrm{}$ and $x=0.5\mathrm{}$ single crystals using angle-resolved photoemission. A narrow band, characteristic of many-body effects, develops near $E_F$ for $x=0.5\mathrm{}$. This feature shifts away from $E_F$ at the transition temperature, a discontinuous change at the metalinsulator transition in a Mott-Hubbard system. We discuss our data in the context of recent theoretical calculations of the Hubbard model. The spectra support the general finding that a narrow peak of many-body nature develops at $E_F$ during the insulator-to-metal transition.