TEMPERATURE-DEPENDENT BREAKDOWN OF LINEAR SCREENING IN THE QUANTUM HALL REGIME

It is shown that the linear Thomas-Fermi screening for an electron gas in a triangular well subjected to a quantising magnetic field always breaks down at sufficiently low temperatures. This is not the case for an ideal 2DEG. The Thomas-Fermi parameter Q approaches a constant value in the low-temperature limit, whereas for an ideal 2DEG it varies as T-1. Further it is shown that a lateral confined electron system is surrounded by broad depletion regions caused by electrons trapped in surface states at the lithographic boundaries. The widths of the depletion regions are estimated from the difference in energy between the conduction band level and the level of the surface states. As an example of nonlinear screening the authors consider the QHE breakdown in a narrow channel and show that the observed linear dependence between the critical voltage for breakdown and B-Bi can be explained if the electrons in the channel are considered as a non-metallic region. Here Bi corresponds to i filled Landau levels, i being an integer. A reasonable agreement with experimental results is obtained.