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.
@article{arxiv.1506.05137,
title = {Switchable Coupling of Vibrations to Two-Electron Carbon-Nanotube Quantum Dot States},
author = {P. Weber and H. L. Calvo and J. Bohle and K. Goß and C. Meyer and M. R. Wegewijs and C. Stampfer},
journal= {arXiv preprint arXiv:1506.05137},
year = {2015}
}