Electronic structure of and covalency driven metal-insulator transition inBaCo1-xNixS2 - art. no. 045111

We investigate the evolution of the electronic structure across the metal-t o-insulator transition in the isostructural series, BaCo1-xNixS2, using ele ctron spectroscopic studies. Our experimental results show a progressive de pletion of the spectral intensity at and near the Fermi level across the se ries, with decreasing x. Analysis of the core-level and valence-band photoe mission spectra in conjunction with detailed many-body calculations show th at the ground state of the system is highly covalent. We estimate the elect ronic structure parameters of the system and deduce that the hopping intera ction strength t(pd) decreases in the solid solution with a decrease of the Ni content, while U-dd and Delta do not change appreciably. Thus, the meta l-to-insulator transition in this system is found to be driven primarily by covalency effects, though the static disorder in the system is expected to play an important role in determining the details of physical properties.