Observations of two-fold shell filling and Kondo effect in a graphene nano-ribbon quantum dot device

TL;DR

This study investigates the electronic transport properties of a graphene nanoribbon quantum dot, revealing shell filling, broken valley degeneracy, and Kondo resonance, indicating complex spin and edge state interactions.

Contribution

First observation of two-fold shell filling and Kondo effect in a graphene nanoribbon quantum dot device, highlighting edge state influence.

Findings

Two-fold shell filling observed in Coulomb blockade measurements

Kondo-like resonance with symmetric conductance peaks detected

Splitting of Kondo resonance suggests spin polarization due to edge states

Abstract

A graphene nanoribbon (GNR) with orientation along its principle axis was obtained through a mechanical tearing process, and a quantum dot device was fabricated from the GNR. We have studied the transport property of the GNR quantum dot device down to dilution refrigerator temperatures. Two-fold charging periodicity was observed in the Coulomb-blockade measurement, signaling a shell-filling process with broken valley degeneracy. In one of the smaller Coulomb diamonds, Kondo-like resonance were observed, with two conductance peaks displaced symmetrically from the zero bias voltage. The splitting of Kondo resonance at zero magnetic field suggests spin-polarization of the quantum dot, possibly due to the edge states of a zigzag GNR.