Direct measurement of bulk currents in the quantized Hall regime

The integer quantized Hall effect reveals a state of scattering-free carrier transport and quantized resistance in a two-dimensional conductor exposed to a perpendicular magnetic field. The quantized resistance is observed for the Hall bar geometry, i.e., if the current carrying contacts are connected by sample edges. A widely accepted model is the Landauer-Buttiker picture, which assumes an incompressible, i.e., electrically insulating bulk state surrounded by one-dimensional edge channels giving rise to quantized resistance. This model is challenged by the screening theory, which takes into account electron-electron interaction and predicts for the quantized Hall plateaus current flow in incompressible strips, which gradually shifts from the sample edges into the bulk with increasing magnetic field. We present direct proof of the predicted scattering-free bulk transport by exploring a Hall bar augmented with an additional contact placed in its center away from the Hall bar edges. Our result supports the screening theory.