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 φ and level position ε. In the unitary limit, G(φ) reaches its maximum 2e²/h at φ0ex0ex=0ex0exπ/2. We find a Fano-suppressed Kondo plateau for G(ε) similar to recent experiments.