Density of States and Energy Gap in Andreev Billiards
  We present numerical results for the local density of states in semiclassical Andreev billiards. We show that the energy gap near the Fermi energy develops in a chaotic billiard. Using the same method no gap is found in similar square and circular billiards. 
A. Lodder (Amsterdam) and Yu. V. Nazarov (Delft, The Netherlands)