Robert J. Joynt

Anderson Model in a Superconductor: $Φ$-Derivable Theory

We introduce a new $Φ$-derivable approach for the Anderson impurity model in a BCS superconductor. The regime of validity of this conserving theory extends well beyond that of the Hartree-Fock approximation. This is the first generalization of the U-perturbation theory to encompass a superconductor.