Evidences for Metal-Insulator Phase Coexistence Below Tc in Self-doped Manganite Films

We present evidence for the existence of a significant insulating phase component more that 100 K below the magnetic ordering temperature in the self-doped system La$_{0.80}$MnO3. Reflectivity measurements were made over the range 100 to 8000 cm-1. Using the Drude-Lorenz Model, we convert reflectivity spectra into optical conductivity spectra. The insulating phase was evident as sharp resonances corresponding to atomic vibrational modes which disappeared deep in the metallic phase at low temperature. A significant component of the insulating phase exists down to 200 K below Tc. Between 200 K and 150 K, the metallic phase becomes the dominant phase. Comparisons are made with the La0.7Ca0.3MnO3 samples measured under the same conditions.