A generalized proximity effect model in superconducting bi- and   tri-layer films
  This paper presents a general model for calculating the density of states and the Cooper pair potential in proximity coupled superconducting bi- and tri-layer films. The typical example of superconducting tunnel junctions is used to show that the model is working. 
G.Brammertz, A. Poelaert, A. A. Golubov, P.Verhoeve, A. Peacock, H.   Rogalla