DRASTIC SUPPRESSION OF SCATTERING AND ACTIVATED BEHAVIOR IN MESOSCOPIC QUANTUM HALL SYSTEMS WITH SMOOTH CONFINEMENT

It is shown that in a degenerate two-dimensional electron gas (2DEG), intralevel intracenter electron transitions due to a strong impurity p otential, for not too low temperatures, can lead to the observed activ ated behavior of the resistivity in micrometer- or submicrometer-width parabolic channels. This contribution is exponentially suppressed if the Fermi level is not too close to the bottom of the nearest Landau l evel. As the temperature decreases, at fixed confining potential, this activated behavior is changed to a temperature-independent behavior t hat is usual for elastic scattering of the degenerate 2DEG. The latter is related with intralevel interedge electron transitions. The asymme try of the Shubnikov-de Haas oscillations and their dependence on conf inement and temperature are obtained in agreement with experimental ob servations.