Coherent Kondo-lattice state and the crossover transitions in the Anderson-lattice model

Abstract

We study the formation of the coherent Kondo-lattice state responsible for the heavy-fermion quasiparticle state in the Anderson-lattice model, and discuss the crossover transitions between the incoherent and coherent Kondo-lattice states, and between the coherent Kondo-lattice state and the valence-fluctuation state. The f-electron lattice Green function is obtained in the self-consistent equation-of-motion method in the decoupling approximation, and is found to have a characteristic feature of lattice different from the impurity Green function. The overall f-electron densities of states are studied as a function of temperature. In the Kondo-lattice regime, as temperature decreases, the crossover transition from the incoherent to the coherent Kondo-lattice states takes place before the single-site Kondo resonances are fully developed at individual sites. Thus the lattice Kondo effect is distinct from the impurity one. The coherent Kondo-lattice state, which has a sharp pseudogap at the Fermi level, fully develops at the coherence temperature ${T}_{0}$\ensuremath{\sim}0.1${T}_{K}$, which is in agreement with the experimental results.