Raman scattering study of anomalous charge-, spin-, and lattice-dynamics in the charge-ordered phase of ${\mathbf{B}\mathbf{i}}_{1-x}{\mathbf{C}\mathbf{a}}_x{\mathbf{M}\mathbf{n}\mathbf{O}}_3$ ($x>0.5$)

We report an inelastic light scattering study of the effects of charge-ordering on the spin-, charge-, and lattice-dynamics in ${\rm Bi}{1-x}{\rm Ca}{x}{\rm MnO}_3$ $(x>0.5)$. We find that charge-ordering results in anomalous phonon behavior, such as the appearance of `activated’ modes. More significantly, however, the transition to the CO phase results in the appearance of a quasielastic scattering response with the symmetry of the spin chirality operator ($T_{1g}$); this scattering response is thus indicative of magnetic or chiral spin fluctuations in the AFM charge-ordered phase.