Magnetic impurity coupled to interacting conduction electrons.

We consider a magnetic impurity which interacts by hybridization with a system of weakly correlated electrons and determine the energy of the ground state by means of an 1/Nf expansion. The correlations among the conduction electrons are described by a Hubbard Hamiltonian and are treated to lowest order in the interaction strength. We find that their effect on the Kondo temperature, TK, in the Kondo limit is twofold: First, the position of the impurity level is shifted due to the reduction of charge fluctuations, which reduces TK. Secondly, the bare Kondo exchange coupling is enhanced as spin fluctuations are enlarged. In total, TK increases. Both corrections require intermediate states beyond the standard Varma-Yafet ansatz. This shows that the Hubbard interaction does not just provide quasiparticles, which hybridize with the impurity, but also renormalizes the Kondo coupling. 75.20.Hr, 75.30.Hx, 71.28.+d 71.27.+a Typeset using REVTEX 1