Switchable Coupling of Vibrations to Two-Electron Carbon-Nanotube Quantum Dot States

TL;DR

This study demonstrates the ability to electrically control the coupling between vibrational modes and two-electron states in a suspended carbon nanotube quantum dot, revealing selective coupling to specific electronic states and interactions.

Contribution

It introduces a method to switch vibrational coupling on and off in a carbon nanotube quantum dot and uncovers unique coupling to two-electron states not explained by standard models.

Findings

Electrostatic tuning controls vibration coupling.

Coupling occurs only with the two-electron spin-triplet state.

Coupling involves valley degree of freedom and exchange interaction.

Abstract

We report transport measurements on a quantum dot in a partly suspended carbon nanotube. Electrostatic tuning allows us to modify and even switch 'on' and 'off' the coupling to the quantized stretching vibration across several charge states. The magnetic-field dependence indicates that only the two-electron spin-triplet excited state couples to the mechanical motion, indicating mechanical coupling to both the valley degree of freedom and the exchange interaction, in contrast to standard models.