Tunable few-electron double quantum dots and Klein tunnelling in ultra-clean carbon nanotubes

TL;DR

This paper demonstrates the creation of tunable single and double quantum dots in ultra-clean carbon nanotubes, revealing novel Klein tunneling phenomena that enhance control over electron confinement.

Contribution

It introduces a method to confine single electrons in tunable quantum dots within ultra-clean nanotubes, enabling new studies of relativistic-like tunneling effects.

Findings

Successful confinement of single electrons in tunable quantum dots

Observation of Klein tunneling-like behavior in nanotube devices

Enhanced tunability of quantum dot barriers in ultra-clean nanotubes

Abstract

Quantum dots defined in carbon nanotubes are a platform for both basic scientific studies and research into new device applications. In particular, they have unique properties that make them attractive for studying the coherent properties of single electron spins. To perform such experiments it is necessary to confine a single electron in a quantum dot with highly tunable barriers, but disorder has until now prevented tunable nanotube-based quantum-dot devices from reaching the single-electron regime. Here, we use local gate voltages applied to an ultra-clean suspended nanotube to confine a single electron in both a single quantum dot and, for the first time, in a tunable double quantum dot. This tunability is limited by a novel type of tunnelling that is analogous to that in the Klein paradox of relativistic quantum mechanics.