Fontein et al.463 have used the bir

Fontein et al.463 have used the birefringence of GaAs induced by an electric field to perform a contactless measurement of the electrostatic potential distribution in a Hall bar. They measure the Hall potential profile VH(x) as a change in the local electrostatic potential if a current is passed through the Hall bar. The data points shown in Fig. 80 were taken at 1.5K for two magnetic field values on the plateau of quantized Hall resistance at 14h/e2. The potential varies steeply at the edges (at x = ±1mm in Fig. 80) and is approximately linear in the bulk. The spatial resolution of the experiment was 70 μm, limited by the laser beam used to measure the birefringence. The current distribution is not directly measured, but can be estimated from the guiding center drift (4.2) (this assumes a slowly varying potential). The nonequilibrium current density i(x) along the Hall bar is then given by