IMAGING OF THE DISSIPATION IN QUANTUM-HALL-EFFECT EXPERIMENTS

The spatial distribution of heat dissipation in quantum-Hall-effect devices was imaged utilizing the fountain pressure effect of superfluid helium. This was done by observing visually the local thickness of a helium film covering the sample. We found that dissipation takes place only in two opposite corners at the current contacts. Unexpected asymmetries between the two corners were observed if the Hall currents exceeded a threshold value. A new and striking dissipative effect was found when current is passed from narrow to wide 2 DEG areas which also was asymmetric upon current reversal.