Potential distribution on multiple bridge devices in quantizing magnetic fields

Abstract

We investigated the local potential distribution on multibridge structures in high magnetic fields made on the basis of GaAs/GaAlAs heterostructures. The samples provide six bridges with different widths ranging from 2 to 100 mu m connected in parallel. The various bridges were found to have different current-voltage characteristics. Negative voltages were detected over some of the bridges in a distinct current range. This is due to non-local edge conduction and can be explained if one considers the inner boundaries between the bridges as regions of macroscopic localized states. These states remain decoupled from the outer boundaries in the quantum Hall regime as long as the longitudinal conductivity sigma xx tends to zero. From the data for the longitudinal resistivity and the Hall resistivity as functions of the magnetic field measured on outer contacts, we calculated the Hall voltage for the single bridges using Ohm's and Kirchhoff's laws. The corresponding experimental curves show a similar shape but smaller plateau ranges in comparison with the dependences calculated in this local approach. Complete agreement between the experimental results on single bridges and the calculations can be obtained if the widths of the current paths for bulk conduction in the various parts of the samples are allowed to deviate from the geometrical widths. The results then indicate an oscillating width of the current path similar to the oscillations in the longitudinal resistivity rho xx.