Vortices associated with the wave function of a single electron emitted   in slow ion-atom collisions
  We present measurements and calculations of the momentum distribution of electrons emitted during the ion-atom collision 10 keV/u $He^{2+}+He \rightarrow He^{+} + He^{2+} + e^{-}$, which show rich structures for ion scattering angles above 2 mrad arising dominantly from two-electron states. Our calculations reveal that minima in the measured distributions are zeros in the electronic probability density resulting from vortices in the electronic current. 
L. Ph. H. Schmidt, C. Goihl, D. Metz, H. Schmidt-B\"ocking, R.   D\"orner, S. Yu. Ovchinnikov, J. H. Macek, and D. R. Schultz
physics.atom-ph