Observation of charge-density-wave excitations in manganites

In the optical conductivity of four different manganites with commensurate charge order ( CO), strong peaks appear in the meV range below the ordering temperature T(CO). They are similar to those reported for one-dimensional charge density waves (CDW) and are assigned to pinned phasons. The peaks and their overtones allow one to obtain, for La(1-n/8)Ca(n/8)MnO(3) with n = 5, 6, the electron-phonon coupling, the effective mass of the CO system, and its contribution to the dielectric constant. These results support a description of the CO in La-Ca manganites in terms of moderately weak coupling and of the CDW theory.