Physical Mechanism in Kondo Insulator

Physical mechanism in Kondo insulator with nearly homogeneous energy gap is studied based on the model for the valence fluctuation regime in which the mixing band electron is of localized character and the first excited state is a s -wave exciton. This model is applied to new experimental studies by the inelastic neutron scattering in SmB 6 and YbB 12 , as well as their alloys. Therefore, the present model is based on the effective one site Kondo state model. The Luttinger theorem is also critically studied on this stand point. Detailed q -dependence of the s -wave exciton peak in SmB 6 is calculated based on the present model. Good agreement is obtained even though there is no adjustable parameter. In particular, two peak structure along both [111] and [011] directions with the intensity ratio of 3:1, as well as the sharp q dependences are explained very well. Anomalous behaviors in the alloy systems are also well explained based on the present model.