ENERGY-BAND THEORY OF THE INVERSE METAL-INSULATOR-TRANSITION IN UNISN

A theoretical explanation of the inverse metal-insulator transition in UNiSn is proposed. Ab initio energy-band calculations, which account for strong on-site Coulomb correlations between the uranium Sf-electro ns provide a fully satisfactory description of the metallic antiferrom agnetic phase as well as of the semiconducting paramagnetic phase, for which a band gap of 0.12 eV is calculated. The valence states are fou nd to interact strongly with the semilocalized, completely polarized S f-electrons through polarization dependent hybridization and exchange interaction. Antiferromagnetic ordering is calculated to lead via this interaction to a closing of the band gap, and it thereby brings about the inverse metal-insulator transition.