At specific values of external magnetic field B, and under microwave irradiation (red arrow), the conductance of a two-dimensional electron (e-, generated by a nearby filament) gas on the surface of liquid helium falls to zero. Credit: 2011 Denis Konstantinov and Kimitoshi Kono
Trapping electrons in a flat plane prevents them from moving freely in the third dimension and opens the door to a whole range of unusual physics. These effects are harnessed, for example, in modern ultrafast transistors, which confine electrons to thin layers of high-quality semiconductor crystals such as gallium arsenide. But scattering from impurities in semiconductors can mask the deeper underlying physics of these so-called two-dimensional electron gases (2DEGs). Liquid helium may provide an alternative to semiconductors since it is largely impurity free. Using this approach, Denis Konstantinov and Kimitoshi Kono from the RIKEN Advanced Science Institute (Japan) have demonstrated a novel effect where light totally switches off the conductivity of 2DEGs.