Orbital fluctuating state in ferromagnetic insulating LaMnO3+δ (0.085≤δ≤0.125) studied using Raman spectroscopy

A giant softening by $30\phantom{\rule{0.3em}{0ex}}{\mathrm{cm}}^{\ensuremath{-}1}$ of the 490 and $620\phantom{\rule{0.3em}{0ex}}{\mathrm{cm}}^{\ensuremath{-}1}$ Jahn-Teller and breathing optical phonon modes is observed in Raman spectroscopy below the Curie temperature of single crystalline $\mathrm{La}\mathrm{Mn}{\mathrm{O}}_{3+\ensuremath{\delta}}$ $(0.085\ensuremath{\leqslant}\ensuremath{\delta}\ensuremath{\leqslant}0.125)$. A pseudogaplike suppression of a continuum and a Fano antiresonance at $144\phantom{\rule{0.3em}{0ex}}{\mathrm{cm}}^{\ensuremath{-}1}$ appear below the charge-ordering temperature. Upon going through the antiferromagnetic/ferromagnetic insulating phase boundary a high-frequency maximum of three-peaks structure evolves to a unstructured, broadened maximum while undergoing a softening in the peak energy. This is interpreted in terms of the presence of fluctuating orbitals and mobile holes which form a stripelike state in the lightly doped, insulating manganites.