Superconducting Pairing Amplitude and Local Density of States in   Presence of Repulsive Centers
  We study the properties of superconductor in presence of a finite concentration of repulsive centers. The superconductor is described by the negative $U$ Hubbard model while repulsive centers are treated as randomly distributed impurities with repulsive interaction. Analyzing the paring potential and local density of states at impurity sites we find a wide range of the system parameters where the $\pi$ - like state could possibly be realized. Comparison of our results to the single repulsive center case is also given. 
Grzegorz Litak, Mariusz Krawiec