Interplay between the coherent and incoherent transport in quantum Hall   bilayers
  We systematically study the coherent transport (Josephson tunneling and counterflow current) and its breakdown which leads to incoherent charge flow in in the excitonic BCS condensate formed in GaAs bilayers at $\nu_{tot}=1/2+1/2$. The Josephson currents in samples with three different interlayer distances vary by four orders of magnitude. In contrast, the breakdown thresholds for the $\nu_{tot}=1$ quantum Hall state are comparable. Furthermore, Coulomb drag in a Corbino ring reveals that the coherent counterflow current coexists with the dissipative charge transport. 
Ding Zhang, Xuting Huang, Werner Dietsche, Maik Hauser, Klaus von   Klitzing
cond-mat.mes-hall