MAGNETIZATION OF A CLEAN QUANTUM-DOT IN A TIME-DEPENDENT FLUX - RESTORATION OF AHARONOV-BOHM OSCILLATIONS BY INELASTIC-SCATTERING

We discuss criteria for discriminating between ballistic' and 'clean' quantum structures created in the 2D electron gas of gated semiconduct or heterostructures and show that they are different for impurity pote ntial fluctuations of shea and long range. For long-range fluctuations , such as in high-mobility modulation-doped heterostructures, we show that the criterion for the system to be clean-so that impurity scatter ing is not at all important-can be met. Hence, disorder-induced gaps i n the electron spectrum can be ignored while considering dynamical pro perties in a time-dependent magnetic field even at a relatively low ra te of change. The magnetization of a 2D clean quantum dot turns out to be very sensitive to inelastic relaxation processes in the system. In contrast to the usual destructive role played by inelastic scattering in mesoscopic phenomena, here inelastic scattering restores an Aharon ov-Bohm type of quantum oscillation in the magnetization. In the absen ce of such relaxation, strong nonequilibrium behaviour suppresses thes e oscillations in favour of large diamagnetic moments. We discuss the special type of inelastic backscattering responsible for relaxation in the case of an isolated dot. By monitoring the transient behaviour of the induced magnetic moment as the magnetic field is switched from on e value to another we propose to measure the characteristic time of in elastic backscattering estimated to be of the order of 10(-8)-10(-7) s econds.