Quantum Interference above 4.2K in a GaAl_0.3As_0.7/GaAs Aharonov-Bohm Ring

Magneto-conductance measurements of a micron sized GaAl_0.3As_0.7/GaAs Aharonov-Bohm device has been performed at temperatures above T = 4.2K, in the regime where only a few transverse modes are occupied. We find that the Aharonov-Bohm oscillations are still visible at these relatively high temperatures. The electron density of the Aharonov-Bohm device was during the measurements controlled via a gate voltage applied to a small stub which was attached to one arm of the ring. Due to this highly asymmetric gate configuration the electron density in the ring is strongly asymmetric, and hence an oscillating conductance as a function of gate voltage is expected - in analogy with the Mach-Zender interferometer.