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.

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