Theory of magnetic excitations in the Kondo lattice

Abstract

We present a theory for the spin excitations of the Kondo lattice. We derive an effective Hamiltonian, which describes Fermionic spin 1/2 charge fluctuations interacting with Bosonic triplet spin fluctuations. We show that already the simplest approximation possible, i.e. replacing the magnon self-energy by the free polarization bubble for the charge excitation Greens function, gives a quantitative description of the `spin gap' and `charge gap' as obtained in numerical calculations for the Kondo insulator.