The Aharonov-Bohm oscillations in t

The Aharonov-Bohm oscillations in the magnetoresistance of a small ring in a high-mobility 2DEG are quite impressive. As an illustration, we reproduce in Fig. 26 the results obtained by Timp et al.201 Low-frequency modulations were filtered out, so that the rapid oscillations are superimposed on a constant background. The amplitude of the h/e oscillations diminishes with increasing magnetic field until eventually the Aharonov-Bohm effect is completely suppressed. The reduction in amplitude is accompanied by a reduction in frequency. A similar observation was made by Ford et al.74 In metals, in contrast, the Aharonov-Bohm oscillations persist to the highest experimental fields, with constant frequency. The different behavior in a 2DEG is a consequence of the effect of the Lorentz force on the electrons in the ring, which is of importance when the cyclotron diameter 2lcycl becomes smaller than the width W of the arm of the ring, provided W < l (note that lcycl = hkF/eB is much smaller in a 2DEG than in a metal, at the same magnetic field value). We will return to these effects in Section IV.D.