Kondo Effect in Single Quantum Dot Systems --- Study with Numerical Renormalization Group Method ---

TL;DR

This study uses the Numerical Renormalization Group method to analyze the Kondo effect in single quantum dot systems with two active orbitals, revealing how conductance varies with temperature and gate voltage.

Contribution

It demonstrates the differing Kondo temperatures for each orbital and explores the complex conductance behaviors arising from orbital interactions and temperature effects.

Findings

Kondo temperature varies significantly between orbitals.

Conductance exhibits non-monotonic behavior with temperature.

Interference effects can suppress conductance at zero temperature.

Abstract

The tunneling conductance is calculated as a function of the gate voltage in wide temperature range for the single quantum dot systems with Coulomb interaction. We assume that two orbitals are active for the tunneling process. We show that the Kondo temperature for each orbital channel can be largely different. The tunneling through the Kondo resonance almost fully develops in the region $T \lsim 0.1 T_{K}^{*} \sim 0.2 T_{K}^{*}$, where $T_{K}^{*}$ is the lowest Kondo temperature when the gate voltage is varied. At high temperatures the conductance changes to the usual Coulomb oscillations type. In the intermediate temperature region, the degree of the coherency of each orbital channel is different, so strange behaviors of the conductance can appear. For example, the conductance once increases and then decreases with temperature decreasing when it is suppressed at T=0 by the interference cancellation between different channels. The interaction effects in the quantum dot systems lead the sensitivities of the conductance to the temperature and to the gate voltage.