The Fano-Kondo effect in semiconductor quantum dots

We report observation of the Fano-Kondo effect in semiconductor quantum dot-wire hybrid systems. The Fano effect originates from the rapid change of phase shift by pi at a quantum dot when the energy of incident electrons passes through a resonant point and results in distorsion in the spectrum of the transition probability. When it is combined with the Kondo effect, the lineshape of the conductance versus the gate voltage (i.e., the electron energy) reflects not only transmission probability but also the characteristic phase shift, e.g., locking to pi/2 in the case of SU(2) Kondo effect. First in a quantum wire with a side-coupled quantum dot, clear Fano-Kondo effect with distortion parameter q = 0 has been observed. That is, the Kondo resonant transmission at Coulomb valleys has appeared as a revresed lineshape in the conductance, which verifies quantum coherence of the Kondo effect and at the same time, evidences phase shift locking to pi/2. When an Aharonov-Bohm (AB) ring interferometer is adopted, the distortion parameter q can also be modified by the AB flux resulting in direct confirmation of the phase shift locking effect.