Decoherence of the Kondo singlet caused by Fano resonance

We investigate the structure of an Aharonov-Bohm interferometer with a quantum dot coupling to left and right electrodes. By employing cluster expansions, the equations of motion of Green's functions are transformed into the correspond- ing equation of motion of connected Green's functions, which provides a truncation scheme. With this method under the Lacroix's truncation approximation, we show that Fano resonance causes a decoherence of the Kondo singlet. PACS: 73.23.-b, 73.63.-b, 72.15.Qm, 75.20.Hr