  Dark soliton excitations are shown to exist in single wall carbon nanotubes
(SWCNTs). At first, the nonlinear effective interatomic potential and the
difference equation for longitudinal lattice displacement are obtained for the
SWCNTs by expanding Brenner's many-body potential in a Taylor series up to
fourth-order terms. Then using a multi-scale method, for short wavelength
lattice excitations the equation of motion of lattice is reduced to the cubic
nonlinear Schrodinger equation. Finally, the dark soliton solutions and
relevant excitations in the SWCNTs with subsonic velocity are discussed.
