Fano and Fano-Kondo resonance in double quantum dot in parallel

It has been a controversial issue whether the Fano resonance is observed or not in the transport through a mesoscopic ring with an embedded quantum dot, so-called Aharonov-Bohm interferometer. To address this issue, we theoretically examine the nonequilibrium transport through a double quantum dot (DQD) in parallel: resonant tunneling at the Coulomb peak or Kondo effect in the Coulomb valley in quantum dot 1, with a broad linewidth in quantum dot 2. Our model is more tractable than a model for the AB interferometer [1]. We stress the importance of multiple channels in external leads to simulate the experimental systems, which was often neglected in previous studies. In the case of single channel in the leads, we find an asymmetric Fano resonance or Fano-Kondo resonance as a function of energy level in quantum dot 1. With an increase in the number of channels, these approach the symmetric Breit-Wigner resonance or Kondo plateau. This is because the coherence between the quantum dots is weakened, which can be characterized by the off-diagonal element normalized by the diagonal elements in a two-by-two matrix of the linewidth function.
[1] W. Hofstetter et al., Phys. Rev. Lett. 87, 156803 (2001).