POTENTIAL DISTRIBUTION ON MULTIPLE BRIDGE DEVICES IN QUANTIZING MAGNETIC-FIELDS

We investigated the local potential distribution on multibridge struct ures in high magnetic fields made on the basis of GaAs/GaAlAs heterost ructures. The samples provide six bridges with different widths rangin g from 2 to 100 mu m connected in parallel. The various bridges were f ound to have different current-voltage characteristics. Negative volta ges 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 macr oscopic localized states. These states remain decoupled from the outer boundaries in the quantum Hall regime as long as the longitudinal con ductivity sigma(xx) tends to zero. From the data for the longitudinal resistivity and the Hall resistivity as functions of the magnetic fiel d measured on outer contacts, we calculated the Hall voltage for the s ingle bridges using Ohm's and Kirchhoff's laws. The corresponding expe rimental curves show a similar shape but smaller plateau ranges in com parison with the dependences calculated in this local approach. Comple te agreement between the experimental results on single bridges and th e calculations can be obtained if the widths of the current paths for bulk conduction in the various parts of the samples are allowed to dev iate from the geometrical widths. The results then indicate an oscilla ting width of the current path similar to the oscillations in the long itudinal resistivity rho(xx).