${}^{13}\mathrm{C}$ NMR evidence for dynamics of nanotubes in ropes

We report on ${}^{13}\mathrm{C}$ nuclear magnetic resonance from $10$ up to $350$ K on single wall carbon nanotubes. The magic angle spinning NMR spectrum shows one isotropic line at $126$ ppm and the static spectrum a powder pattern typical for a curved graphene sheet. The T dependence of the spin-lattice relaxation rate $T_1^{-1}$ reveals an unusual phenomenon which could be explained by thermally activated small amplitude motion (SAM) of the nanotubes. If above $170$ K, diffusion of twistons might be responsible for the local SAM of the ${}^{13}\mathrm{C}$ sites, below this transition temperature frozen in twistons could appear with an orientational order of the nanotubes in the ropes.