Crossover from dilute-Kondo system to heavy-fermion system

Ground-state properties of a Kondo lattice model with random configuration of f electrons are investigated with a variational Monte Carlo method. We show that the crossover from a dilute-Kondo system to a heavy-fermion system occurs when the density of c and f electrons (n_c, n_f) become comparable, n_f n_c. In the heavy-fermion region, the correlation between f electrons is strong and the f electrons themselves greatly contribute to the screening of other f -electron moments. We propose that the character of Kondo screening changes from "individual" to "collective" across the crossover.