ULTRASONIC APPROACH TO THE INTEGER AND FRACTIONAL QUANTUM HALL-EFFECT

The integer and fractional quantum Hall effect is investigated using t he acoustoelectric effect in a high mobility two-dimensional electron system. This effect is a result of the interaction of the coherent fie ld of an ultrasonic surface acoustic wave and the completely quantized electron system in strong magnetic fields. The mutual interaction lea ds to both energy and momentum transfer of the wave to the electrons a nd is reflected in giant quantum oscillations in the sound-induced cur rents and voltages in the two-dimensional system. Unlike standard magn etotransport experiments the acoustoelectric effect probes the states of the bulk of the electron system rather than those of the edges and thus is suited to gain insight into the quantum Hall effect from a dif ferent point of view.