Lattice dynamics and charge ordering inLa1−xCaxMnO3(0.45<~x<~0.76)

Abstract

We study local lattice fluctuations in ${\mathrm{La}}_{1\ensuremath{-}x}{\mathrm{Ca}}_{x}{\mathrm{MnO}}_{3}$ $(0.45l~xl~0.76)$ by means of inelastic light scattering. Fluctuation effects are especially strong in the intensity variation of Jahn-Teller mode at 480 ${\mathrm{cm}}^{\mathrm{\ensuremath{-}}1}$ around commensurate doping $x\ensuremath{\approx}0.5.$ The linewidth of the Jahn-Teller mode shows a minimum at $x=0.50$ indicating ``long-range'' lattice and charge commensuration at low temperatures. The electron-phonon interaction is fundamentally changed at the transition to the charge-ordered (CO) state as evidenced by sign and magnitude changes in the Fano parameter. Temperature-dependent data show enhanced fluctuations persisting up to temperatures of at least 2 ${T}_{\mathrm{co}}$ for $x\ensuremath{\approx}0.50.$