Asymmetric Anderson Model and Spin Excitations in the Kondo Insulator YbB_(12)

摘要

A cluster problem is analyzed as an example demonstrating that the observed three-mode behav_ior of spin-triplet excitations in YbB_(12) can be described by the asymmetric Anderson model with insulating singlet ground state. In the case of an infinite system, it is argued that the behavior of the f subsystem can be analyzed by using an effective Hamiltonian H_J with direct antifenomagneticf_f exchange interaction. The spin excitation spectrum is shown to have a minimum at the antiferromagnetic vector, as observed experimen_tally. A distinctive feature of the analysis is the use of singlet and triplet basis operators.