Antiferromagnetism and Kondo effect in a two quantum dot system: a slave boson approach.

I. J. HAMAD; L. COSTA RIBEIRO; E. V. ANDA

Aguas de Lindoia

Conferencia; XXXV Encontro Nacional de Materia Condensada; 2012

Sociedade Brasileira de Fisica

In a recent experiment, Jakob et. al [1] proposed a device consisting of a cobalt atom attached to the tip of a scanning tunneling microscope (STM) which interacts with another Co atom adsorbed on a gold surface. The high capacity to tune the tip-sample distance obtained by the authors, with a subpicometre resolution, enabled the control of the electronic interaction between the two Co atoms and allowed the access to a very rich set of physical phenomena, specifically, those associated to the interplay of the antiferromagnetic interaction between the spins of the Co atoms and the Kondo correlation with the electronic reservoir spins. As well, it is possible to carefully study the geometrical aspects of the experimental disposition creating Fano antiresonances in the differential conductance as a function of the applied potential. In order to reproduce the physics observed in such an experiment we elaborate a model consisting of two sites where the electrons are highly correlated, that simulates the two Co atoms. Each atom interacts with an electronic reservoir and between themselves by means of a directed coupling and also, indirectly, through a coupling between the two electronic reservoirs. The many- body system is solved using a Slave Boson Formalism, solving the problem in the mean field approximation for finite values of U, the Coulomb electronic repulsion at the Co sites. Unlike the NRG calculations developed in the mentioned work, which partially explain the measurements, our results carries the physics information associated to the direct coupling between the Co atoms that permits to study the different regimes and the geometrical implications on the conductance results. Our study is able to explain the experimental results in all the parameter space. [1] Jakob Bork, Yong-hui Zhang, Lars Diekhoner, Lszl Borda, Pascal Simon, Johann Kroha, Peter Wahl, and Klaus Kern.