Zero-field splitting of the Kondo resonance and quantum criticality in triple quantum dots

TL;DR

This paper investigates a triple quantum dot system revealing how interference and quantum phase transitions influence the Kondo effect and conductance, with implications for understanding quantum criticality in nanoscale devices.

Contribution

It maps a triple quantum dot system onto a single-impurity Anderson model and explores quantum criticality and interference effects using Numerical Renormalization Group methods.

Findings

Splitting of the Kondo peak due to interference effects.

Identification of a quantum phase transition between Kondo and non-Kondo states.

Observation of Fano-Kondo effect influenced by quantum criticality.

Abstract

We consider a triple-quantum-dot (TQD) system composed by an interacting quantum dot connected to two effectively non-interacting dots, which in turn are both connected in parallel to metallic leads. As we show, this system can be mapped onto a single-impurity Anderson model with a non-trivial density of states. The TQD's transport properties are investigated under a continuous tuning of the non-interacting dots' energy-levels, employing the Numerical Renormalization Group technique. Interference between single and many-particle resonances splits the Kondo peak, fulfilling a generalized Friedel sum rule. In addition, a particular configuration in which one of the non-interacting dots is held out of resonance with the leads allows to access a pseudogap regime where a Kosterlitz-Thouless type quantum-phase-transition (QPT) occur, separating the Kondo and non-Kondo behavior. Within this same configuration, the TQD exhibits traces of the Fano-Kondo effect, which is in turn, strongly affected by the QPT. Signatures of all these phenomena are neatly displayed by the calculated linear conductance.