Vortex Drag in Quantum Hall Effect
  A new model of momentum and electric field transfer between two adjacent 2D electron systems in the Quantum Hall Effect is proposed. The drag effect is due to momentum transfer from the vortex system of one layer to the vortex system of another layer. The remarkable result of this approach is periodical change of $sign$ of the dragged electric field with difference between the layer filling factors. 
S. A. Vitkalov