Transport in Coherent Quantum Hall Bilayers
  We discuss two phenomenological descriptions of low-current transport in bilayer quantum Hall system with exciton condensates, one based on a Landauer-Buttiker description of Andreev scattering at contacts to coherent bilayers and one based on a simplified single-parameter {\em p-ology} description of the weak to strong interlayer coupling crossover. The Andreev scattering phenomenology in intended to apply when the condensate is well developed and is used to predict current-voltage relationships for a variety of two contact geometries. We also apply this formalism to circumstances in which the tunnel current exceeds its critical value and the condensate is time-dependent. The {\em p-ology} approach is used to establish the universal development of large longitudinal drags, even in homogenous coherent samples, as the condensate weakens and the Hall drag is reduced. 
D. A. Pesin, and A. H. MacDonald
cond-mat.mes-hall