2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/28091We study the formation of a heavy-fermion state in the 2D periodic Anerson model. For U=2, the density of states, imaginary part of the self-energy and effective magnetic moment all indicate the Kondo screening of local f electrons, leading to a coherent heavy-fermion state. For U=3 and 4, the dominance of RKKY interaction over Kondo screening at low temperatures indicates a magnetic instability at zero temperature. A partial screening of magnetic moments, however, still gives rise to a relatively sharp peak at the Fermi energy in the density of states.5 pages, revtex, 5 figuresCondensed Mattertext