Superconductivity and antiferromagnetism: Hybridization impurities in a two-band spin-gapped electron system

We present the exact solution of a one-dimensional model of a spin-gapped c orrelated electron system with hybridization impurities exhibiting both mag netic and mixed-valence-properties. The host supports superconducting fluct uations with a spin gap. The localized electrons create a band of antiferro magnetic spin excitations inside the gap for concentrations x of the impuri ties below some critical value x(c). When x=x(c), the spin gap closes and a ferrimagnetic phase appears. This is an example of an exactly solvable mod el with coexisting superconducting and antiferromagnetic fluctuations, whic h in-addition supports a quantum phase transition to a(compensated) ferrima gnetic phase. We discuss the possible relevance of our results for experime ntal systems, in particular the U-based heavy fermion materials. [S0163-182 9(99)01345-4].