Edge State Transport in Separately Contacted Double-Layer Quantum Hall   Systems
  We develop a theory of edge state transport in separately contacted double-layer quantum Hall systems which are tuned close to the resonance condition for tunneling between the layers. When applied to the case where contact is made to only one layer, the theory gives a quantized Hall resistance and zero longitudinal resistance in both weak and strong inter-layer coupling limits. For weak coupling, the leading correction to the Hall resistance occurs at second order, while the longitudinal resistance appears at first order. Recent experiments which show almost quantized Hall resistance and a substantial longitudinal resistance are explained and predictions are made for other contact configurations. 
D. Yoshioka and A.H. MacDonald