Symmetric, gated, ballistic rings as tunable electron interferometers

In the present work we investigate the coherent electron transport in a symmetrically designed ballistic ring uniformly covered by a top metal gate. We find that as the Fermi energy is varied, the phase of Aharonov–Bohm (AB) oscillations near zero magnetic field switches between 0 and π. It seems unlikely that this behaviour can be explained by some accidental asymmetry in the structures. We give a qualitative explanation of our results using a model where the ring is considered to be weakly coupled to the leads and the conductance is calculated on the basis of an exact energy spectrum of an ideal ring. This model predicts that a variation of the phase of AB oscillations with gate voltage may be observed in a symmetrical ring.