Andreev Spectroscopy of Josephson Coupling
  It is shown that the low energy spectrum of mesoscopic superconductors coupled by Josephson interaction can be probed by two-electron tunneling from a normal electrode. The Andreev reflection in the NS junction of a normal-superconductor-superconductor double junction (NSS transistor) provides a unique spectroscopic tool to probe the coherent Cooper pair tunneling and the energy spectrum of the Josephson (SS) junction. The ground state properties are reflected in a resonant structure of the linear conductance; excited states with an energy as low as the Josephson coupling energy lead to a threshold in the nonlinear $I$-$V$ characteristic. 
F.W.J. Hekking, L. I. Glazman, and Gerd Schoen