Direct Observation of Born-Oppenheimer Approximation Breakdown in Carbon Nanotubes

TL;DR

This study provides the first experimental evidence of the breakdown of the Born-Oppenheimer approximation in individual carbon nanotubes, observed through Raman spectra and conductance measurements under varying gate voltages.

Contribution

It experimentally confirms the theoretical prediction of Born-Oppenheimer approximation breakdown in carbon nanotubes using Raman and electrical measurements.

Findings

G-band downshifts at small gate voltages, minima at EF = +/- 1/2 Ephonon

Raman shift exhibits a 'W'-shaped profile at higher voltages

Results align with a non-adiabatic phonon renormalization model

Abstract

Raman spectra and electrical conductance of individual, pristine, suspended, metallic single-walled carbon nanotubes are measured under applied gate potentials. The G- band is observed to downshift with small applied gate voltages, with the minima occurring at EF = +/- 1/2 Ephonon, contrary to adiabatic predictions. A subsequent upshift in the Raman frequency at higher gate voltages results in a 'W'-shaped Raman shift profile that agrees well with a non-adiabatic phonon renormalization model. This behavior constitutes the first experimental confirmation of the theoretically predicted breakdown of the Born-Oppenheimer approximation in individual single walled carbon nanotubes.