Transverse electron focusing in a two-dimensional electron gas is mvestigated expenmentally and theoretically for the flrst time. A split Schottky gate on top of a GaAs-Al x Ga,_^As heterostructure defines two point contacts of variable width, which are used äs mjector and collector of ballistic electrons As evidenced by their quantized conductance, these are quantum point contacts with a width comparable to the Fermi wavelength At low magnetic flelds, skipping orbits at the electrongas boundary are directly observed, thereby establishing that boundary scattenng is highly specular Large additional oscillatory structure in the focusing spectra is observed at low temperatures and for small pomt-contact size This new phenomenon is mterpreted in terms of mterference of coherently excited magnetic edge states m a two-dimensional electron gas A theory for this effect is given, and the relation with nonlocal resistance measurements in quantum ballistic transport is discussed It is pomted out, and expenmentally demonstrated, that four-termmal transport measurements m the electron-focusmg geometry constitute a determmation of either a generalized longitudmal resistance or a Hall resistance At high magnetic fields the electron-focusmg peaks are suppressed, and a transition is observed to the quantum Hall regime The anomalous quantum Hall effect m this geometry is discussed m light of a four-termmal resistance formula
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