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 correlated electron system with hybridization impurities exhibiting both magnetic and mixed-valence properties. The host supports superconducting fluctuations, with a spin gap. The localized electrons create a band of antiferromagnetic spin excitations inside the gap for concentrations x of the impurities below some critical value x_c. When x = x_c the spin gap closes and a ferrimagnetic phase appears. This is the first example of an exactly solvable model with coexisting superconducting and antiferromagnetic fluctuations which in addition supports a quantum phase transition to a (compensated) ferrimagnetic phase. We discuss the possible relevance of our results for experimental systems, in particular the U-based heavy-fermion materials. 
A. A. Zvyagin and H. Johannesson