The fine structure on the focusing

The fine structure on the focusing peaks in Fig. 53 is the first indication that electron focusing in a 2DEG is qualitatively different from the corresponding experiment in metals. At higher magnetic fields the resemblance to the classical focusing spectrum is lost; see Fig. 54. A Fourier transform of the spectrum for B ≥ 0.8T (inset in Fig. 54) shows that the large-amplitude highfield oscillations have a dominant periodicity of 0.1 T, which is approximately the same as the periodicity Bfocus of the much smaller focusing peaks at low magnetic fields (Bfocus in Fig. 54 differs from Fig. 53 because of a smaller L = 1.5 μm). This dominant periodicity can be explained in terms of quantum interference between the different skipping orbits from injector to collector or in terms of interference of coherently excited edge channels, as we discuss in the following subsection. The experimental implication is that the injector acts as a coherent point source with the coherence maintained over a distance of several microns to the collector.