Abstract
It is shown that collective modes can emerge in the Kondo insulator which is described as an ordered state of conduction–f electron–hole (\(\bar{c}\)–f) pair fields in the symmetric case of the Kondo lattice model (KLM). The one-loop approximation is adopted in a functional integral formalism similar to that developed by Popov for the s-state superfluid Fermi system (SFS). The massless Nambu–Goldstone (NG) mode due to the phase fluctuation of \(\bar{c}\)–f pair fields possesses a quadric dispersion, differently from a linear one for the SFS, and the massive Higgs mode due to the amplitude fluctuation has a gap 2Δ, twice the fermionic gap, similarly to the SFS. Because of the quadric dispersion of the NG mode, similar to the ferromagnetic spin wave mode, the specific heat of the KLM is expected not to be an activation-type but to exhibit a T3/2-dependence, which may be confirmed experimentally.
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