  We discovered in simulations of sliding coaxial nanotubes an unanticipated
example of dynamical symmetry breaking taking place at the nanoscale. While
both nanotubes are perfectly left-right symmetric and nonchiral, a nonzero
angular momentum of phonon origin appears spontaneously at a series of critical
sliding velocities, in correspondence with large peaks of the sliding friction.
The non-linear equations governing this phenomenon resemble the rotational
instability of a forced string. However, several new elements, exquisitely
"nano" appear here, with the crucial involvement of Umklapp and of sliding
nanofriction.
