Kondo Correlations and the Fano Effect in Closed Aharonov-Bohm Interferometers

We study the Fano-Kondo effect in a closed Aharonov-Bohm (AB) interferometer which contains a single-level quantum dot and predict a frequency doubling of the AB oscillations as a signature of Kondo-correlated states. Using the Keldysh formalism, the Friedel sum rule, and the numerical renormalization group, we calculate the exact zero-temperature linear conductance $G$ as a function of the AB phase $\varphi$ and level position $\epsilon$. In the unitary limit, $G\left(\varphi \right)$ reaches its maximum ${2e}^2/h$ at $\varphi =\pi /2\mathrm{}$. We find a Fano-suppressed Kondo plateau for $G\left(\epsilon \right)$ similar to recent experiments.