Channel interference in a quasiballistic Aharonov-Bohm experiment

New experiments are presented on the transmission of electron waves through a two-dimensional electron gas ring with a gate on top of one of the branches. Magnetoconductance oscillations are observed, and the phase of the Aharonov-Bohm signal alternates between 0 and pi as the gate voltage is scanned. A Fourier transform of the data reveals a dominant period in the voltage, interpreted as the energy spacing between successive transverse modes. A theoretical model including random phase shifts between successive modes reproduces the essential features of the experiment.