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 electro n system (2DES) under quantum Hall conditions at a temperature T = 1.4 K. W e mapped out the Hall potential profiles for the Landau level filling facto r range 1 < nu < 14 with submicron resolution. At integer filling factors, the potential drop is rather nonlinear, but depends strongly on the scan po sition. Obviously inhomogeneities of the sample strongly affect the Hall po tential profile if the bulk of the 2DES is nonconductive and cannot screen. At filling factors slightly above an even integer value, the Hall potentia l drops at prominent positions at both edges which are associated with the positions of the incompressible strips as confirmed by comparison with theo retical predictions. With these broad incompressible strips electrically de coupling the edge region from the compressible bulk region, a nearly vanish ing Hall potential drop is observed in the compressible bulk region, sugges ting that most of the current is flowing close to the edges. In addition, p otential 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.