Abstract
We report an electronic Raman scattering study of the colossal magnetoresistance (CMR) manganese perovskites as a function of temperature, magnetic field, symmetry, and doping. The low-frequency electronic Raman spectrum in the paramagnetic-insulating phase of these materials is characterized by a diffusive Raman-scattering response, while a nearly flat continuum response is observed in the ferromagnetic-metallic state. We found that the ${B}_{1g}$-symmetry electronic scattering intensity is significantly reduced with applied magnetic field near ${T}_{C},$ in a manner reminiscent of the dc magnetoresistivity. The strongly field-dependent scattering rate in the ${B}_{1g}$ channel appears to reflect the highly field-dependent mobility along the Mn-O bond direction expected in the double exchange mechanism. In addition, we observe a persistent field dependence in the ${B}_{1g}$ electronic scattering response for $T\ensuremath{\ll}{T}_{C},$ suggesting that the ferromagnetic phase is inhomogeneous, perhaps consisting of both metallic and insulating components.
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