2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/170923It is pointed out that the answer on the question about the role played by spin and charge excitations will help to solve the physical origin of the heavy- fermion phenomena. Our answer is that neutral spin-like excitations are responsible for the heavy-fermion phenomena whereas the role of the charge excitations is negligible. Keywords: heavy fermion, spin excitations, charge excitations PACS No: 75.20.H7 pages in RevTex, no figuresStrongly Correlated Electronstext