Fano-Kondo effect in side-coupled double quantum dots at finite temperatures and the importance of the two-stage Kondo screening

TL;DR

This paper investigates the interplay of Fano and Kondo effects in a double quantum dot system at finite temperatures, revealing how two-stage Kondo screening influences conductance line shapes and offers new interpretations of experimental data.

Contribution

It provides a detailed analysis of the temperature-dependent conductance in side-coupled double quantum dots, highlighting the role of two-stage Kondo screening in shaping Fano-like resonances.

Findings

Fano resonance shape depends on the interaction strength of the side dot.

Two-stage Kondo effect can produce Fano-like conductance anti-resonances.

Temperature influences the line-shape significantly, especially in the strongly interacting regime.

Abstract

We study the zero-bias conductance through the system of two quantum dots, one of which is embedded directly between the source and drain electrodes, while the second dot is side-coupled to the first one through a tunneling junction. Modeling the system using the two-impurity Anderson model, we compute the temperature-dependence of the conductance in various parameter regimes using the numerical renormalization group. We consider the non-interacting case, where we study the extent of the departure from the conventional Fano resonance line shape at finite temperatures, and the case where the embedded and/or the side-coupled quantum dot is interacting, where we study the consequences of the coexistence of the Kondo and Fano effects. If the side-coupled dot is very weakly interacting, the occupancy changes by two when the on-site energy crosses the Fermi level and a Fano-resonance-like shape is observed. If the interaction on the side-coupled dot is sizeable, the occupancy changes only by one and a very different line-shape results, which is strongly and characteristically temperature dependent. These results suggest an intriguing alternative interpretation of the recent experimental results study of the transport properties of the side-coupled double quantum dot [Sasaki et al., Phys. Rev. Lett. 103, 266806 (2009)]: the observed Fano-like conductance anti-resonance may, in fact, result from the two-stage Kondo effect in the regime where the experimental temperature is between the higher and the lower Kondo temperature.