Classical and weak localization processes in a tunable ballistic-electron cavity

The appeal of the lateral surface gate technique lies in the ability to tune the device through application of variable gate bias. We apply positive bias to a 250-nm-wide continuous gate, or stripe, defined above the two-dimensional electron gas of an ${\mathrm{Al}}_{\mathit{x}}$ ${\mathrm{Ga}}_{1\mathrm{-}\mathit{x}}$As/GaAs heterostructure. Following pulsed light emitting diode illumination, inhomogeneities in the region shielded by the stripe can be annealed by tuning the positive bias. We employ this technique to introduce trajectory scrambling events into a ballistic-electron cavity. Through a systematic study of the low-field magnetoresistance of the cavity as a function of positive stripe bias (tuning the inhomogeneities) and temperature (control of electron phase coherence), we examine the interplay between geometry-induced weak localization and classical transport phenomena. In contrast to other recent observations of weak localization in the ballistic regime, our cavity is relatively large (1.8×30 μ${\mathrm{m}}^2$) and the trajectory loops are defined, not by the confining walls of the cavity, but by the profile of the exit port.