Gate-voltage dependence of Kondo effect in a triangular quantum dot

TL;DR

This study investigates how the Kondo effect in a triangular quantum dot varies with gate voltage, revealing different Kondo regimes, conductance dips, and a two-stage screening of a local magnetic moment.

Contribution

It demonstrates the gate-voltage dependence of multiple Kondo effects, including SU(4) and S=1 Kondo phenomena, in a triangular quantum dot system using NRG calculations.

Findings

SU(4) Kondo effect at half-filling

Conductance dip due to phase lapse

Two-stage screening of S=1 moment

Abstract

We study the conductance through a triangular triple quantum dot, which are connected to two noninteracting leads, using the numerical renormalization group (NRG). It is found that the system shows a variety of Kondo effects depending on the filling of the triangle. The SU(4) Kondo effect occurs at half-filling, and a sharp conductance dip due to a phase lapse appears in the gate-voltage dependence. Furthermore, when four electrons occupy the three sites on average, a local S=1 moment, which is caused by the Nagaoka mechanism, is induced along the triangle. The temperature dependence of the entropy and spin susceptibility of the triangle shows that this moment is screened by the conduction electrons via two separate stages at different temperatures. The two-terminal and four-terminal conductances show a clear difference at the gate voltages, where the SU(4) or the S=1 Kondo effects occurring.