$\pi-$shifted magnetoconductance oscillations in mesoscopic   superconducting-normal-heterostructures
  Interference of proximity induced superconducting correlations in mesoscopic metallic rings is sensitive to the magnetic flux $\Phi$ inside these rings. This is the reason for magnetoconductance oscillations in such systems. We detected experimentally and explained theoretically a novel effect: the phase of these oscillations can switch between 0 and $\pi$ depending on the resistance of intermetallic interfaces and temperature. The effect is due to a nontrivial interplay between the proximity induced enhancement of the local conductivity and the proximity induced suppression of the density of states at low energies. 
V.N.Antonov, H.Takayanagi, F.K. Wilhelm, and A.D.Zaikin