Kondo screening of a high-spin Nagaoka state in a triangular quantum dot

TL;DR

This paper investigates how conduction electrons screen a high-spin Nagaoka state in a triangular quantum dot, revealing a two-stage Kondo screening process and distinct conductance behaviors in different configurations.

Contribution

It demonstrates the occurrence of a two-stage Kondo screening of a high-spin Nagaoka state in a triangular quantum dot using NRG calculations, highlighting unique transport properties.

Findings

Two-stage Kondo screening of S=1 state observed.

Series conductance is suppressed to near zero.

Parallel conductance reaches the quantum limit of 4e^2/h.

Abstract

We study transport through a triangle triple quantum dot connected to two noninteracting leads using the numerical renormalization group (NRG). The triangle has a high-spin ground state of S=1 caused by a Nagaoka ferromagnetism, when it is isolated and has one extra electron introduced into a half-filling. The results show that the conduction electrons screen the local moment via two separate stages with different energy scales. The half of the S=1 is screened first by one of the channel degrees, and then at very low temperature the remaining half is fully screened to form a Kondo singlet. The transport is determined by two phase shifts for quasi-particles with even and odd parities, and then a two-terminal conductance in the series configuration is suppressed $g_{\rm series} \simeq 0$, while plateau of a four-terminal parallel conductance reaches a Unitary limit value $g_{\rm parallel} \simeq 4e^2/h$ of two conducting modes.