Two Quantum Dot Systems: Interplay of RKKY interaction and Kondo effect.

L. COSTA RIBEIRO; I. J. HAMAD; G. CHIAPPE; G. B. MARTINS; E. V. ANDA

Dresden

Conferencia; International Conference on Superlattices, Nanostructures and Nanodevices.; 2012

It is theoretically well established that two quantum dots (QD ́s) interacting between themselves via conduction electrons give rise to physical phenomena dominated by the competition between Kondo physics and the RKKY interaction. However, there is no experimental clear evidence of the interplay of these two effects. In a recent experiment, Jakob et. al [1], within the scope of these phenomena, studied a system consisting of two magnetic atoms, one attached to the tip of a scanning tunneling microscope and the other adsorbed on a goldsurface. The experiment permits to control the electronic interaction between the two Co atoms and allows the access to a very rich set of physical phenomena. In order to simulate the physics observed in such an experiment, we propose a theoretical model consisting of two sites where the electrons are highly correlated, that represent the two Co atoms. Each atom interacts with an electronic reservoir and between themselves by means of a direct coupling and also, indirectly, through a coupling between the two electronic reservoirs. The many-body system is solved using two different approaches: a Slave Boson Formalism [2] in the mean field approximation for finite values of the Coulomb electronic repulsion at the Co site and also the Logarithmic Discretization Embedded Cluster Approximation [3]. The model studied is able to explain qualitatively and semi-quantitatively the variation of the experimental differential conductance results in all the parameter space. Within this same formalism we show that the effect of the RKKY interaction on the conductance depends very much upon the geometry of the system. We propose, in particular, a geometrical configuration, shown in fig1, that results to be very appropriate to understand this problem. We analyze the transport properties of this structure composed by two quantum dots with strong Coulomb interaction $U$ interconnected through N non-interacting sites and coupled to two electronic reservoir. These systems allow us to study the effect of the RKKY interaction on the conductance that exhibits the competition of Kondo and RKKY physics. We discuss a variety of scenarios and propose that a measurement of the conductance is the appropriate experiment to be done, not only to study these two quantum regimes and the crossover region between them, but as well to read the quantum information associated with the sign of the RKKY interaction between the QD’s.