RESPONSE FUNCTION OF A 2-DIMENSIONAL ELECTRON-GAS IN A UNIDIRECTIONALPERIODIC POTENTIAL

The dynamical density-response function of a periodically modulated tw o-dimensional electron gas under a perpendicular magnetic field is cal culated within the random-phase approximation. It is found that the re sponse function is not only broadened by the periodic potential, it al so contains a series of subsingularities at the band edges. The maximu m number of subsingularities is 2n(max), where n(max) is the number of occupied Landau levels (the last level may be partially filled). It i s further proposed that light-scattering or electromagnetic absorption experiments can be performed to study these predicted structures.