Many-body Regime Research Articles

Competing local exchange mechanisms: a validity test of a simple scaling hypothesis

The interplay of a direct ferromagnetic exchange interaction I>0 between local and band states and an indirect antiferromagnetic exchange -J<0 via hybridization V is studied using an expanded version of the Anderson impurity model in the highly correlated regime. A simple scaling idea is put forward for the dependence of the free energy, one-particle spectra, T-matrix and susceptibility on the size of hybridization and direct exchange. It describes the many-body regime J>>I in terms of a universal picture as well as the crossover near J approximately=I to the trivial regime J<<I, the latter being characterized by an effective elastic one-particle scattering problem. These physical arguments are supported by extensive numerical calculations in the framework of perturbation theory with respect to I and V. It is also indicated how I may be included into new post-NCA theories of the Kondo effect.