Mesoscopic Fano effect through a quantum dot in an Aharonov–Bohm ring

The Fano effect illustrates how the interference and resonance cooperatively occur between a discrete state and a continuum energy state. We have realized a tunable Fano system by fabricating a quantum dot embedded in an Aharonov–Bohm ring on a two-dimensional electron gas. In the Coulomb oscillation, clear asymmetric lineshapes were observed, which manifests the formation of the Fano state, namely, a mixture of the discrete state and the continuum state. The non-equilibrium transport and the temperature dependence reveal the essential role of the coherence for this effect. Through the phase controlling by the magnetic flux piercing the ring, Fanoʹs asymmetric parameter q is obtained as a complex number for the first time.