“…In non-degenerate semiconductor films with a QSE this dependence is smoother because of a more uniform occupancy of quantized states. Though we do not know of any direct observation of such sawor step-like curves in transport measurements without magnetic field (with the exception of, maybe, reference [11]), the QSE has been observed in both metal and semiconductor films (see, e.g., references [12,13] and references therein) by scanning tunnelling microscopy [14], ultraviolet electron spectroscopy, photoemission, and dozens of other optical experimental techniques (see references [3,15] and references therein). Recently a QSE has also been observed in confined 3 He at ultralow temperatures [16].…”