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Frictional Drag Between Parallel Conducting Layers

Frictional Drag Between Parallel Conducting Layers

The frictional drag experiment is a novel probe of the properties of bilayer systems. The concept is similar to conventional friction and is illustrated below. A current is driven in one layer (the drive layer), and interlayer electron-electron interactions transfer momentum to a nearby layer (the drag layer). The drag layer is conventionally in an open circuit configuration, where no drag current is allowed to flow. A voltage therefore builds up in the drag layer to counteract the drag force, which gives a direct measure of the interlayer electron-electron scattering rate.

Schematic diagram of the drag experimentFigure 1: Schematic diagram of the drag experiment.

The drag relies on inhomoeneities in the two layers, otherwise the each layer experience only a smooth potential from the adjacent layer. These inhomogeneities are density fluctuations within each layer, and the fluctuations in the two layers are coupled either by the Coulomb or Phonon interactions. The drag measurement therefore probes both the excitations within the layers and the interlayer interaction.

Within the Semiconductor Physics group the frictional drag experiment has been used to probe the bilayer plasmon modes, and has also been investigated in the QH regime.