Hidden symmetry and the magnetically induced `Mott transition' in quantum wells containing an electron gas

The magnetoluminescence spectra of symmetric quantum wells containing an electron gas show an abrupt transition from Landau level behavior (i.e. a linear shift of energy with field) to quadratic (exciton-like) behavior as the magnetic field is increased. This so-called `Mott transition' always occurs at the field at which the electron filling factor v<sub>e</sub> is 2, i.e. when the lowest Landau level is just filled. We show that the transition is a natural consequence of a hidden symmetry which has been shown to hold in two-dimensional systems at high fields. The mechanism driving it has nothing to do with that driving the true Mott transition, and it would be better named a `symmetry-driven transition'.