EFFECT OF FINITE CONCENTRATION IN KONDO ALLOYS - APPROACH TO THE HEAVY-FERMION PROBLEM

By using Nozières' Fermi-liquid formulation for magnetic impurities as scattering centers at low temperatures (T<TK), we calculate the x2 correction terms (in the impurity concentration) to the thermodynamic potential. We interpret the difference in the low-temperature properties between some cerium- and uranium-based alloys in terms of how close the scattering phase shift δ for an isolated impurity center is to the unitary limit (δ=π/2). We apply a picture of independent impurity centers for a large range of x in some Ce-based alloys, but only for x1 in U-based alloys. This is due to the Ce-based alloys being much closer to the unitary limit than the U-based alloys, suggesting that in the formation of a collective ground state the change in the density of states is the dominant effect in a dense Kondo lattice where the single-center phase shift is close to the unitary limit, while the magnetic interaction between local-impurity centers becomes important in a system where the phase shift differs from π/2. © 1995 The American Physical Society.