On the experimental focusing peaks

On the experimental focusing peaks a fine structure is resolved at low temperatures (below 1 K). The fine structure is well reproducible but sample-dependent. A nice demonstration of the reproducibility of the fine structure is obtained upon interchanging current and voltage leads, so that the injector becomes the collector, and vice versa. The resulting focusing spectrum shown in Fig. 53 (trace b) is almost the precise mirror image of the original one (trace a), although this particular device had a strong asymmetry in the widths of injector and collector. The symmetry in the focusing spectra is an example of the general reciprocity relation (3.16). If one applies the B¨uttiker equations (3.12) to the electron focusing geometry (as is done in Section IV.B), one finds that the ratio of collector voltage Vc to injector current Ii is given by