Decorating „Hot Spots“ at the integer quantum Hall effect
In the quantum Hall effect regime, the longitudinal resistance tends to vanish while the Hall resistance shows quantized values. This means that inside the sample the lines of constant electric potential must run parallel to the edges of the sample. However, to match the potential landscape at the contacts where the potential lines run perpendicular to the current, one has to invoke “hot spots” in one corner of each contact. In these hot spots nearly all dissipation of the quantum-Hall effect takes place.
Using the fountain effect of superfluid helium, we managed to visualize the hot spots. This effect leads to an easily visible drop in the helium film covering the sample at the hot spots. The animation shows the effect of turning the current on (drops visible) and off (no drops can be seen).