Raman spectroscopy of the charge-orbital ordering in layered manganites

The lattice and electronic response in the course of concomitant charge and orbital-ordering transition has been investigated for single crystals of layered manganites, single-layered (Formula presented) and bilayered (Formula presented) by Raman-scattering spectroscopy. In the charge-orbital-ordered state (Formula presented) K for (Formula presented) and (Formula presented) K for (Formula presented) four phonon modes are activated in the (Formula presented) plane, indicating the existence of both Jahn-Teller type and breathing mode type lattice distortions. The diffuse scattering response with (Formula presented) symmetry is suppressed in the charge-orbital-ordered state, both for (Formula presented) and (Formula presented) signaling that the fluctuation caused by the dynamical charge-orbital correlation is suppressed in the charge-orbital-ordered state. These features reveal the unique nature of the charge-orbital-ordering transition realized by the complex interplay of charge and orbital degrees of freedom.