Eur. Phys. J. B 67, 231–238 (2009) DOI: 10.1140/epjb/e2009-00012-0 Regular Article T HE EUROPEAN P HYSICAL JOURNAL B Fano effect in a double T-shaped interferometer V. Moldoveanu 1, a , I.V. Dinu 1 , and B. Tanatar 2 1 National Institute of Materials Physics, P.O. Box MG-7, 077125 Bucharest-Magurele, Romania 2 Department of Physics, Bilkent University, Bilkent, 06800 Ankara, Turkey Received 25 August 2008 / Received in final form 10 November 2008 Published online 20 January 2009 – c  EDP Sciences, Societ`a Italiana di Fisica, Springer-Verlag 2009 Abstract. We study the coherent transport in a one-dimensional lead with two side-coupled quantum dots using the Keldysh’s Green function formalism. The effect of the interdot Coulomb interaction is taken into account by computing the first and second order contributions to the self-energy. We show that the Fano interference due to the resonance of one dot is strongly affected by the fixed parameters that characterize the second dot. If the second dot is tuned close to resonance an additional peak develops between the peak and dip of the Fano line shape of the current. In contrast, when the second dot is off-resonance and its occupation number is close to unity the interdot Coulomb interaction merely shifts the Fano line and no other maxima appear. The system we consider is more general than the single-dot interferometer studied experimentally by Kobayashi et al. [Phys. Rev. B 70, 035319 (2004)] and may be used for controlling quantum interference and studying decoherence effects in mesoscopic transport. PACS. 73.23.Hk Coulomb blockade; single-electron tunneling – 85.35.Ds Quantum interference devices – 85.35.Be Quantum well devices – 73.21.La Quantum dots 1 Introduction The level structure of quantum dot systems is very sen- sitive to the potentials applied on the metallic gates that define them. In particular, one can match a discrete level of the quantum dot to the continuous spectrum of the in- cident electrons from leads. This tunability is nowadays widely used to study resonant transport and quantum in- terference effects in various structures (for recent reviews see Refs. [1,2]). A typical example is the experiment of Kobayashi et al. [3] in which the measured conductance of a quantum wire with a side-coupled quantum dot shows asymmetric Fano line shapes [4] as a function of the gate potential V g applied on the latter. This effect is due to the interference between two types of electronic trajectories within the system: the forward scattered electronic waves and the more complicated paths involving scattering at the dot, i.e., resonant tunnelling processes. A similar ef- fect was previously observed in single-dot Aharonov-Bohm rings [5]. The recent observation of the Fano-Kondo effect [6] in mesoscopic interferometers with a side-coupled quantum dot stimulated many theoretical investigations on strongly correlated transport. Various non-perturbative methods were used to study the formation of the Kondo correlated states in systems composed of a quantum dot which on one hand is coupled to two leads and on the other hand has a second side-coupled dot. a e-mail: valim@infim.ro Kim and Hershfield [7] considered the electronic trans- port through such a system by including the on-site Coulomb interaction in the side-coupled dot, while ne- glecting both the interdot interaction and the Coulomb re- pulsion on the central dot. The interaction self-energy was computed within the non-crossing approximation (NCA) and the spectral functions of the two dots were analyzed. The Kondo scattering was shown to reduce the conduc- tance of the system at low bias. Franco et al. [8] used the X-boson method for the single-impurity model in order to compute the conductance of side-coupled dot systems for weak and strong lateral coupling. Later on Cornaglia and Grempel [9] studied the same system using both numer- ical renormalization group techniques (NRG) and slave- boson mean-field theory (SBMFT). The temperature de- pendence of the conductance was discussed for the case in which the dots are half-filled or when the total charge of the dot is odd or even. We stress that in the approach con- sidered there the Coulomb interaction exceeds all the tun- neling couplings appearing in the problem and therefore the main physical processes are due to spin fluctuations, the occupation on each dot being close to unity. Another interacting regime was investigated by Wu et al. [10] still within SBMFT. In their model the cen- tral dot (i.e., the one which is connected to the leads) operates in the Kondo regime, the side-coupled dot be- ing instead noninteracting. The formula for the density of states was decomposed into a broad Breit-Wigner reso- nance term and a Fano line shape contribution. A com- parison between interacting and noninteracting Fano line shapes of the current in a T -network was presented by