Transport in Carbon Nanotubes: 2LSU(2) regime reveals subtle competition between Kondo and Intermediate Valence states

TL;DR

This paper investigates charge transport in carbon nanotube quantum dots within the 2LSU(2) regime, revealing a subtle competition between Kondo and Intermediate Valence states using advanced numerical techniques.

Contribution

It introduces a detailed analysis of the 2LSU(2) regime derived from an SU(4) model, highlighting the transition from double- to single-channel transport and proposing a new energy scale for experimental analysis.

Findings

Charge transport switches from double- to single-channel in the 2LSU(2) regime.

Gate potential influences occupancy oscillations due to Kondo and Intermediate Valence competition.

The energy scale T_0 helps distinguish the dominant many-body state in the system.

Abstract

In this work, we use three different numerical techniques to study the charge transport properties of a system in the two-level SU(2) (2LSU2) regime, obtained from an SU(4) model Hamiltonian by introducing orbital mixing of the degenerate orbitals via coupling to the leads. SU(4) Kondo physics has been experimentally observed, and studied in detail, in Carbon Nanotube Quantum Dots. Adopting a two molecular orbital basis, the Hamiltonian is recast into a form where one of the molecular orbitals decouples from the charge reservoir, although still interacting capacitively with the other molecular orbital. This basis transformation explains in a clear way how the charge transport in this system turns from double- to single-channel when it transitions from the SU(4) to the 2LSU2 regime. The charge occupancy of these molecular orbitals displays gate-potential-dependent occupancy oscillations that arise from a competition between the Kondo and Intermediate Valence states. The determination of whether the Kondo or the Intermediate Valence state is more favorable, for a specific value of gate potential, is assessed by the definition of an energy scale $T_0$, which is calculated through DMRG. We speculate that the calculation of $T_0$ may provide experimentalists with a useful tool to analyze correlated charge transport in many other systems. For that, a current work is underway to improve the numerical accuracy of its DRMG calculation and explore different definitions.