Critical tunneling currents in the regime of bilayer excitons
  We have investigated the tunneling properties of an electron double quantum well system where the lowest Landau level of each quantum well is half filled. This system is expected to be a Bose condensate of excitons. Our four-terminal dc measurements reveal a nearly vanishing interlayer voltage and the existence of critical tunneling currents which depend on the strength of the condensate state. 
L. Tiemann, W. Dietsche, M. Hauser and K. von Klitzing