Electronic transport through a quantum dot strongly coupled to electrodes is studied within a model with two conduction channels. It is shown that multiple scattering and interference of transmitted waves through both channels lead to Fano resonance associated with Kondo resonance. Interference effects are also pronouncedly seen in transport through the Aharonov-Bohm ring with the Kondo dot, where the current characteristics continuously evolve with the magnetic flux.PACS 72.15.Qm, 75.20.Hr Recent electron transport experiments performed in a single electron transistor strongly coupled to electrodes [1] and by a scanning tunneling microscope (STM) on a single magnetic adatom on a metallic surface [2,3] showed that the Kondo resonance [4] occurs simultaneously with the Fano resonance [5]. Multiple scatterings of travelling electronic waves on a localized magnetic state are crucial for a formation of both resonances. The condition for the Fano resonance to appear is a presence of at least two scattering channels: the discrete level and the broad continuum band [5,6]. In the mesoscopic systems the nature of two conduction channels is dependent on the geometry of the device under consideration. Interferometer geometry is realized when an Aharonov-Bohm ring with a quantum dot (QD) placed in one of the arms is studied [7][8][9]. When an adatom is deposited on the metallic surface, the STM tip probes indirectly the hybridized local adatom level together with the band of surface electrons [2,3,10,11]. We consider the transmission geometry, when the coupling of the QD to the leads increases to a strong regime [1] and additional transmission channels are activated. The QD is a multilevel system and the transmission through a higher level (close to the Fermi energy) can be treated as an effective bridge channel. Although the electron transport through the QD is governed by the Kondo effect, interference processes are essential and can produce the Fano-shaped resonances.It is also interesting to analyze the Aharonov-Bohm ring with the Kondo impurity. In such a system one can continuously change the interference conditions by varying a magnetic flux and can observe the resulting evolution of the current characteristics from the Kondo peak to the Fano dip. The studies have been performed for various energies of the impurity state: in the Kondo regime, in the mixed-valence regime as well as in the empty state regime. Our model is described by the HamiltonianThe first term describes electrons in the in the left (L) and the right (R) electrode; the second one describes the quantum dot with a single state ǫ 0 and Coulomb interactions characterized by the parameter U ; the third one corresponds to the tunneling from the electrodes to the dot; and the last one describes the bridge channel over the dot.The current from the left electrode can be calculated from the time evolution of the occupation number N L = k,σ c † kL,σ c kL,σ for electrons in the left electrode using the Green functions of the Keldysh type [12]. The result is...

No abstract

Linear conductance across a large quantum dot via a single level epsilon(0) with large hybridization to the contacts is strongly sensitive to quasibound states localized in the dot and weakly coupled to epsilon(0). The conductance oscillates with the gate voltage due to interference of the Fano type. At low temperature and Coulomb blockade, Kondo correlations damp the oscillations on an extended range of gate voltage values, by freezing the occupancy of the epsilon(0) level itself. As a consequence, the antiresonances of Fano origin are washed out. The results are in good correspondence with experimental data for a large quantum dot in the semiopen regime.