Hall potential profiles in the quantum Hall regime measured by a scanning force microscope

A low-temperature scanning force microscope sensitive to electrostatics is used to investigate the potential distribution of a two-dimensional electron system (2DES) under quantum Hall conditions at a temperature T = 1.4 K. We mapped out the Hall potential profiles for the Landau level filling factor range 1 < nu < 14 with submicron resolution. At integer filling factors, the potential drop is rather nonlinear, but depends strongly on the scan position. Obviously inhomogeneities of the sample strongly affect the Hall potential profile if the bulk of the 2DES is nonconductive and cannot screen. At filling factors slightly above an even integer value, the Hall potential drops at prominent positions at both edges which are associated with the positions of the incompressible strips as confirmed by comparison with theoretical predictions. With these broad incompressible strips electrically decoupling the edge region from the compressible bulk region, a nearly vanishing Hall potential drop is observed in the compressible bulk region, suggesting that most of the current is flowing close to the edges. In addition, potential profiles near the current injecting contacts reveal the well known hot spot region in the direct vicinity of the contact, but recover to the described shape within a distance of only 6 mum. (C) 2001 Elsevier Science B.V. All rights reserved.