Periodic Orbits and Deformed Shell Structure
  Relationship between quantum shell structure and classical periodic orbits is briefly reviewed on the basis of semi-classical trace formula. Using the spheroidal cavity model, it is shown that three-dimensional periodic orbits, which are born out of bifurcation of planar orbits at large prolate deformations, generate the superdeformed shell structure. 
K. Arita, A.G. Magner and K. Matsuyanagi