UNOCCUPIED ELECTRONIC STATES IN NIS2-XSEX ACROSS THE METAL-INSULATOR-TRANSITION

We investigate the evolution of the electronic structure across the in sulator-metal transition in NiS2-xSex with changing composition, but i n the absence of any structural or magnetic changes. A comparison of t he inverse photoemission spectra with band-structure calculations esta blishes the importance of correlation effects in these systems. System atic changes in the spectral distribution establish the persistence of the upper Hubbard band well into the metallic regime, with the insula tor-to-metal transition being driven by a transfer of spectral weight from the Hubbard band to states close to the Fermi energy.