Singlet-triplet Hamiltonian for spin excitations in a Kondo insulator

摘要

In the nonsymmetric version of the periodic Anderson model for a Kondo insulator, an effective singlet-triplet Hamiltonian ? _(s-t) with indirect antiferromagnetic f-f exchange is constructed, which makes it possible to analyze the dynamic magnetic susceptibility χ _f (k, ω) of f electrons. Hamiltonian ? _(s-t) is used to describe the experimentally observed dispersion of the three-level spin excitation spectrum in YbB_(12). A distinguishing feature of this analysis is the introduction of small-radius singlet and triplet collective f-d excitations that form low- and high-lying spin bands during motion over the lattice.