Charge kinks are considered as fundamental excitations in quarter-filled
charge-ordered ladders. The strength of the coupling of the kinks to the
three-dimensional lattice depends on their energy. The integrated intensity of
Raman scattering by kink-antikink pairs is proportional to $\phi ^{5}$ or $\phi
^{4},$ where $\phi $ is the order parameter. The exponent is determined by the
system parameters and by the strength of the electron-phonon coupling.Comment: To be published in Phys. Rev.B (june 2001