A giant softening by $30{\mathrm{cm}}^{-1}$ of the 490 and $620{\mathrm{cm}}^{-1}$ Jahn-Teller and breathing optical phonon modes is observed in Raman spectroscopy below the Curie temperature of single crystalline $\mathrm{La}\mathrm{Mn}{\mathrm{O}}_{3+\delta }$ $(0.085⩽\delta ⩽0.125)$. A pseudogaplike suppression of a continuum and a Fano antiresonance at $144{\mathrm{cm}}^{-1}$ 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.

• Received 8 April 2006

DOI:https://doi.org/10.1103/PhysRevB.74.064406