Kondo Insulator and Charge Transfer Insulator in Lattice Anderson Model

Abstract

Properties of the heavy-fermion valence-fluctuating compounds leadingto insulating ground states (called Kondo insulators) are investigatedtheoretically by using the U-infinite degenerate lattice Andersonmodel in the auxiliary boson representation. The model is treatedwithin the approximation including terms of the leading order in theexpansion w.r.t. inverse of the spin-orbit degeneracy(1/N-expansion) under the strict local constraints guaranteeingequivalence of the bosonic version to the original U-infinitemodel. The results are compared with the experimental observations onthe possible candidates for Kondo insulators. Differences betweenKondo insulators and charge transfer type insulators now paid muchattention as the mother systems for the high-T_c superconductors are briefly discussed on a unified basis within the model described above.