UNEXPECTED PERIODICITY IN AN ELECTRONIC DOUBLE-SLIT INTERFERENCE EXPERIMENT

We present a controlled interference experiment of ballistic electrons in a two-dimensional electron gas. While the phase along one interfer ing path is kept constant, the phase along the second interfering path is varied using a biased metallic gate, thereby enabling a direct mea surement of the phase accumulated underneath this gate. Surprisingly, in addition to the expected oscillatory signal measured as a function of the gate bias, we observe a longer period signal with approximately half the expected frequency.