Tunable Fano-Kondo resonance in side-coupled double quantum dot system

TL;DR

This paper investigates how the interplay of Fano and Kondo effects in a side-coupled double quantum dot system influences the spectral properties, revealing a two-stage Kondo effect with distinctive double dip-peak features.

Contribution

It introduces a detailed analysis of the Fano-Kondo interplay using RG and NRG methods, highlighting the universal low-energy scaling and the two-stage Kondo effect in the system.

Findings

Double dip-peak features in the Fano lineshape at different energy scales.

Universal scaling behavior at very low energies.

Qualitative agreement between RG and NRG results.

Abstract

We study the interference between the Fano and Kondo effects in a side-coupled double-quantum- dot system where one of the quantum dots couples to conduction electron bath while the other dot only side-couples to the first dot via antiferromagnetic (AF) spin exchange coupling. We apply both the perturbative renormalization group (RG) and numerical renormalization group (NRG) approaches to study the effect of AF coupling on the Fano lineshape in the conduction leads. With particle-hole symmetry, the AF exchange coupling competes with the Kondo effect and leads to a local spin-singlet ground state for arbitrary small coupling, so called "two-stage Kondo effect". As a result, via NRG we find the spectral properties of the Fano lineshape in the tunneling density of states (TDOS) of conduction electron leads shows double dip-peak features at the energy scale around the Kondo temperature and the one much below it, corresponding to the two-stage Kondo effect; it also shows an universal scaling behavior at very low energies. We find the qualitative agreement between the NRG and the perturbative RG approach. Relevance of our work to the experiments is discussed.