Flow-Equation method for a superconductor with magnetic correlations

Abstract

The flow equation method has been used to calculate the energy of single impurity in a superconductor for the Anderson model with $U\ne 0$. We showed that the energy of the impurity depends only of the ${\Delta }_R^2$ (renormalized order parameter) which depends on the renormalized Hubbard repulsion$U^R$. For a strong Hubbard repulsion $U^R=U$ and ${\Delta }^R={\Delta }^I$ the effect of the $s-d$ interactions are nonrelevant, a result which is expected for this model.

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