Conductance in very clean quantum wires and rings

We have observed clear Aharonov-Bohm oscillations in single and multiply connected rings with up to 20% modulation in conductance. The oscillations persist over a very wide range of conductance (0.1-2.0 e2/h) controlled with a gate. Conductance steps as a function of gate bias are observed for the first time in relatively long single and multiple parallel wires and rings. In 2-4 μm long wires, the conductance steps are in multiples of 2e2/h. In the case of the rings, steps of 0.8 and 1.2 e 2/h are observed in one and two loops, respectively.