Dynamical Chiral Symmetry Breaking in Sliding Nanotubes
X.H. Zhang, G.E. Santoro, U. Tartaglino, and E. Tosatti
Simulations in the group of E. Tosatti of AFRI and ACOF CRPs discovered an unanticipated nanoscale example of dynamical symmetry breaking in the sliding of perfectly left-right symmetric and nonchiral nanotubes. At a series of critical sliding velocities, corresponding to large frictional peaks, a nonzero angular momentum of phonon origin appears spontaneously.
Figure 1: (a) Coaxial sliding of (5,5)@(10,10) nanotubes. (b) Sliding friction force per innertube atom and angular momentum JCM versus speed v at T = 300 K. Note the frictional peaks and the threshold near 780 m/s. The nonzero angular momentum signals nanoscale dynamical chiral symmetry breaking in correspondence with the threshold, and with peaks at 570 m/s and 450 m/s. A, B, and C designate related resonance regions, described in text. (c) Outer tube radial motion Fourier spectra with n=2 (green), 3 (blue), and 5 (red) symmetry, showing resonant enhancement in correspondence with peaks and threshold.
We discover in simulations of sliding coaxial nanotubes (Fig. 1, panel (a)) 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 (Fig. 1, panel (b)). The nonlinear 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.
These results recently appeared on Physical Review Letters 102, 125502 (2009), and were simultaneously highlighted in the Physics APS highlights service.
