Flux-dependent level attraction in double-dot Aharonov-Bohm interferometers

We study electron transport through a closed Aharonov-Bohm interferometer containing two noninteracting single-level quantum dots. The quantum-dot levels are coupled to each other indirectly via the leads. We find that this coupling yields signatures of an effective flux-dependent level attraction in the linear conductance. Furthermore, we predict a suppression of transport when both levels are close to the Fermi level of the leads. The width of this anomaly is also flux dependent. We identify different regimes in which constructive interference of transmission through identical dots yields a signal that is 1, 2, or 4 times as large as the conductance through a single dot.