Kondo Peaks and Fano dips in a two Co Atoms System: a theoretical approach.

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

Eindhoven

Conferencia; The 7th International Conference on Physics and Applications of Spin-related Phenomena in Semiconductors; 2012

Eindhoven University of Technology

In a recent experiment, Jakob et. al. [1] studied a system consisting of a cobalt atom attached to the tip of a scanning tunneling microscope which interacts with another Co atom adsorbed on a gold surface. The high capacity to tune the tip-sample distance, 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, specif- ically, those associated to the interplay of the antiferromagnetic interaction between the spins of the Co atoms and the Kondo correlation with the electronic reservoirspins. As well, it was possible to carefull study the ge-ometrical aspects of the experimental disposition creating Fano antiresonances in the differential conduc-tance as a function of the applied potential. 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 cou-pling between the two electronic reservoirs, as shown in Figure 1. We assume an exponential relationship between the couplings tLR and tαβ with a parameter z that emulates de distance between the tip and substrate in the experiment. The many-body system is solved usingtwo different approaches: a Slave Boson Formalism in the mean field approximation [2] 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. We have also calculated the width of the Fano antiresonances and the splitting observed in thedifferential conductance at very short distances, obtaining also a good agreement. We discuss the relationship of our study with the mentioned work and with other experimental and theoretical studies developed for similar systems.References[1] Jakob Bork et al., Nature Physics, Vol. 7, p. 901906 (2011).[2] G. Kotliar and A. E. Ruckenstein, Phys. Rev. Lett. 57, 1362 (1986).[3] E. V. Anda et al., Phys. Rev. B. Vol. 78, 085308 (2008).