Torsional electromechanical quantum oscillations in carbon nanotubes

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Carbon nanotubes1,2 can be distinctly metallic or semiconducting depending on their diameter and chirality3. Here we show that continuously varying the chirality by mechanical torsion4 can induce conductance oscillations, which can be attributed to metal–semiconductor periodic transitions. The phenomenon is observed in multiwalled carbon nanotubes, where both the torque5 and the current are shown to be carried predominantly by the outermost wall6,7. The oscillation period with torsion is consistent with the theoretical shifting8 of the corners of the first Brillouin zone of graphene across different sub-bands allowed in the nanotube. Beyond a critical torsion, the conductance irreversibly drops due to torsional failure, allowing us to determine the torsional strength of carbon nanotubes. Carbon nanotubes could be ideal torsional springs for nanoscopic pendulums4,9,10, because electromechanical detection of motion could replace the microscopic detection techniques used at present. Our experiments indicate that carbon nanotubes could be used as electronic sensors of torsional motion in nanoelectromechanical systems11.