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The temperature (6{endash}350 K) and magnetic-field dependence (0{endash}7.5 T) of the phononic Raman spectra in the layered manganites, R{sub 1.2}Sr{sub 1.8}Mn{sub 2}O{sub 7} (R=La,Nd), reveal anomalous behaviors of the Mn and equatorial O{sub xy}{sup B{sub 1g}} modes arising from local octahedral distortions and coupling to the Mn{sup 3+} e{sub g} electrons. These results provide the evidence for polaron formation and its interplay with electrical transport and magnetism in the layered manganites. {copyright} {ital 1998} {ital The American Physical Society}

Polarized Raman spectra of undoped and doped ${\mathrm{La}}_{1\ensuremath{-}x}{M}_{x}{\mathrm{MnO}}_{3}$ single crystals have been studied in the temperature range from 5 to 423 K ($M=\mathrm{Sr},$ Ca). The spectral intensity is mainly related to scattering by optical phonons at $q\ensuremath{\sim}0$ (for $x\ensuremath{\approx}0$) and the density of vibrational states for $xg0.1.$ Raman spectra from the undoped ${\mathrm{LaMnO}}_{3}$ structure distorted by the static Jahn-Teller effect are consistent with the orthorhombic ${D}_{2h}^{16}$ space group. Raman spectra of the doped ${\mathrm{La}}_{1\ensuremath{-}x}{M}_{x}{\mathrm{MnO}}_{3}$ crystals have weakly resolved features and intensities comparable to those of the second-order spectra in cubic media. The anomalies in the phonon spectra of doped crystals were explained by the doping dependence of the ionic radius of a La/Sr site. The most intense ${B}_{1g}$ mode in ${\mathrm{LaMnO}}_{3}$ crystal has an abrupt frequency shift near ${T}_{N}=140\mathrm{K},$ which corresponds to a paramagnetic to canted-antiferromagnetic phase transition.

Infrared and far-infrared transmittance measurements were performed on Bi{sub 2}Sr{sub 2}CaCu{sub 2}O{sub 8} (2:2:1:2) and Bi{sub 2}Sr{sub 2}CuO{sub 6} (2:2:0:1). Below {ital T}{sub {ital c}}, a characteristic feature occurs at {omega}=700 cm{sup {minus}1} (12{ital k}{sub {ital B}T{ital c}}) in the 2:2:1:2 material. No similar feature is found in the 2:2:0:1 compound. The 2:2:1:2 material also showed substantial {ital ab}-plane anisotropy.

The competition of charge, orbital, and ferromagnetic interactions in layered manganites is investigated by magneto-Raman scattering spectroscopy. We find that the colossal magnetoresistance effect in the layered compounds results from the interplay of the orbital and ferromagnetic double-exchange correlations. Inelastic scattering by charge-order fluctuations dominates the quasiparticle dynamics in the ferromagnetic-metal state. The scattering is suppressed at low frequencies, consistent with the opening of a charge-density wave pseudogap., Comment: 10 pages, 4 figures