author:
Piotr Stefanski Institute of Molecular Physics of the Polish
Academy of Sciences,
ul. Smoluchowskiego 17, 60-179 Poznan,
Poland
Interacting quantum dot side-attached to the metallic wire is the simplest counterpart of magnetic impurity embedded in host metal. Recently, progress in nanotechnology yielded the possibility for such artificial nanoscale devices, which mimic the impurity behavior observed in nature. Moreover, various parameters which are set by chemical bonding in "natural materials" can smoothly be changed in artificial devices by appropriate gate voltages. We calculate conductance through the device of above geometry. A model of quantum dot sideways attached to the wire is conceptually analogous to the Fano model consisting of discrete resonant level and continuos spectrum. However, in the presence of interactions the resonant channel is formed rather by many-body Kondo peak in the vicinity of Fermi surface instead of single-particle quantum dot level. Quantum dots are modeled by Anderson hamiltonian. Calculations of many-body effects have been performed within interpolative perturbative scheme which is an extension of the selfconsistent second order perturbation in Coulomb repulsion U to the atomic limit. This method fulfills Friedel-Langreth sum rule and allows to calculate density of states of a quantum dot coupled to electrodes and conductance for a wide range of parameters, which can be controlled in real experiments. A continuous transition from resonant tunneling (strong coupling to electrodes) to Coulomb blockade regime (weak coupling to electrodes) is also possible during conductance calculation. Conductance is calculated within Landauer formalism in the limit of zero bias. For the wire and one quantum dot coupled sideways to it Kondo effect provides suppression (Fano anti-resonance) of the conductance due to the destructive interference of the electronic waves propagating through direct channel and Kondo channel. The range of the suppression is dependent on Coulomb repulsion U and has a maximum for bare dot level equal to ed=-U/2. When going towards Coulomb blockade regime the conductance suppression starts to be due single-particle dot level and the Kondo resonant channel gradually vanishes. For two quantum dots attached on both sides of the wire two resonant channels are present apart from direct ballistic channel through the wire. When the position of the level inside one quantum dot e1 is continuously shifted from the Kondo regime towards the chemical potential of the wire, while the bare energy level inside the second quantum dot e2 is unchanged, the conductance reaches a minimum when the shifted bare level e1 approaches the value of -U/2. In this case however, the presence of the second side attached quantum dot allows to control the strength of the suppression and the shape of the Fano anti-resonance in the conductance. Depending on the position of e2 the destructive interference of the second quantum dot can be switched off or set to a full range. The second quantum dot (with fixed e2) provides additional background channel; Fano asymmetry parameter is controlled by the position of e2 for such geometry. We hope that our model considerations will stimulate experimental investigations.