Spectral density of an interacting dot coupled indirectly to conducting leads

L. VAUGIER, A.A. ALIGIA AND A.M. LOBOS

PHYSICAL REVIEW B - CONDENSED MATTER AND MATERIALS PHYSICS

APS

Año: 2007 vol. 76 p. 16 - 5112

0163-1829

   We study the spectral density of electrons in an interacting quantum dot QD with a hybridization to a noninteracting QD, which, in turn, is coupled to a noninteracting conduction band. The system corresponds to an impurity Anderson model in which the conduction band has a Lorentzian density of states of width Delta. We solved the model using perturbation theory in the Coulomb repulsion U (PTU) up to second order and a slave-boson mean-field approximation SBMFA . The PTU works surprisingly well near the exactly solvable limit Delta going to 0. For fixed U and large enough or small enough Delta, the Kondo peak in the density of states  splits into two peaks. This splitting can be understood in terms of weakly interacting quasiparticles. Before the splitting takes place, the universal properties of the model in the Kondo regime are lost. Using the SBMFA, simple analytical expressions for the occurrence of split peaks are obtained. For small or moderate Delta, the side bands of the spectral density have the form of narrow resonances that were missed in previous studies using the numerical renormalization group. This technique also has shortcomings for properly describing the split Kondo peaks. As the temperatureis increased, the intensity of the split Kondo peaks decreases, but it is not completely suppressed at high temperatures.