POLARON ABSORPTION IN A PEROVSKITE MANGANITE LA0.7CA0.3MNO3

Optical conductivity spectra of a polycrystalline La0.7Ca0.3MnO3 sampl e were investigated at temperatures between 20 and 300 K. The spectra at a metallic region clearly showed two types of absorption features, i.e., a sharp Drude peak and a broad mid-infrared absorption band. The phonon frequency renormalization occurred with the spectral weight tr ansfer during the metal-insulator transition. Furthermore, the spectra at very low temperatures were quite consistent with the large polaron absorption behavior. A crossover from a small to a large polaron stat e is suggested to explain the observed spectral features.