COUPLED FLUCTUATIONS OF SDW WITH ONE-DIMENSIONAL QUARTER-FILLED BAND

we examine charge and spin fluctuations around the mean-held of a spin density wave (SDW) state with a one-dimensional quarter-filled band b y calculating the excitation spectra of collective modes, spectral wei ghts and static susceptibilities. Both the longitudinal and transverse modes are determined by four kinds of coupled fluctuations which resu lt from the four-fold periodic potential of the commensurate SDW. The interplay of the 2k(F)-SDW and the 4k(F)-CDW appears in the longitudin al fluctuation of both the collective mode and susceptibilities. It is shown that the spectral weight of the longitudinal mode with a gap be comes much larger than that of the transverse mode with a gapless exci tation when the energy of the on-site repulsive interaction is the sam e order of magnitude as the band width.