Dynamics of the charge-density wave. II. Long-range Coulomb effects in an array of chains

In an array of one-dimensional conductors, fluctuations in the phase of the charge-density wave lead to changes in the electron density which are coupled by long-range Coulomb interactions. The Coulomb effect has a profound influence on the dynamics of the charge-density wave as observed by inelastic-neutron scattering. If the momentum transfer equals the Bragg vector of the three-dimensionally-ordered chargedensity wave, it is predicted that almost all of the spectral weight is shifted from the pinning frequency to the plasma frequency ${{\omega }_{\mathrm{pl}}}^{*}$. In ${\mathrm{K}}_2$Pt${\mathrm{}\left(\mathrm{CN}\right)\mathrm{}}_4$ ${\mathrm{Br}}_{0.3}$3.2${\mathrm{H}}_2$O (KCP) this effect is not observed due to the finite transverse correlation length that exists in this system even down to the lowest temperature. The organic conductor tetrathiafulvalene-tetracyanoquinodimethane (TTF-TCNQ), on the other hand, is an excellent candidate for this effect. By combining our results on the dynamics and the neutron scattering experiment on KCP, it is concluded that even the existence of short-range order in KCP is impossible to understand without including the long-range Coulomb effects.