Two-Stage Kondo Effect and Kondo Box Level Spectroscopy in a Carbon Nanotube

TL;DR

This paper explores the two-stage Kondo effect in a carbon nanotube forming a Kondo box, revealing complex spin interactions and conductance behaviors due to competing Kondo states.

Contribution

It provides experimental evidence of the two-stage Kondo effect and compares the observed eigenstates to recent theoretical predictions in a carbon nanotube system.

Findings

Observation of non-monotonic conductance temperature dependence

Identification of competing Kondo states in the nanotube

Analysis of eigenstates consistent with Kondo box theory

Abstract

The concept of the "Kondo box" describes a single spin, antiferromagnetically coupled to a quantum dot with a finite level spacing. Here, a Kondo box is formed in a carbon nanotube interacting with a localized electron. We investigate the spins of its first few eigenstates and compare them to a recent theory. In an 'open' Kondo-box, strongly coupled to the leads, we observe a non-monotonic temperature dependence of the nanotube conductance, which results from a competition between the Kondo-box singlet and the 'conventional' Kondo state that couples the nanotube to the leads.