Phase shift experiments identifying Kramers doublets in a chaotic   superconducting microwave billiard of threefold symmetry
  The spectral properties of a two-dimensional microwave billiard showing threefold symmetry have been studied with a new experimental technique. This method is based on the behavior of the eigenmodes under variation of a phase shift between two input channels, which strongly depends on the symmetries of the eigenfunctions. Thereby a complete set of 108 Kramers doublets has been identified by a simple and purely experimental method. This set clearly shows Gaussian unitary ensemble statistics, although the system is time-reversal invariant. 
C. Dembowski (1), B. Dietz (1), H.-D. Graef (1), A. Heine (1), F.   Leyvraz (2), M. Miski-Oglu (1), A. Richter (1), T. H. Se...