Annealing effects on the optical conductivity of single crystal La1-xCaxMnO3, (x=0.1, 0.265) - art. no. 035106

Optical reflectance spectra were measured in the temperature range 70-295 K , and in the energy range of 0.006-6 eV for single crystals of La1-xCaxMnO3 (x=0.1, 0.265) before and after annealing. The conductivity spectrum of th e unannealed La0.735Ca0.265MnO3 in its low-temperature metallic phase featu res a Drude-like peak, the spectral weight of which is dramatically increas ed by annealing the sample. Annealing also repairs a negative anomaly in th e conductivity, which is thought to be associated with a surface layer dama ged by polishing. A secondary ion mass spectrometry measurement shows, howe ver, that the surface valence becomes depth dependent upon annealing. On th e basis that the skin depth is far greater than the extent of annealing dam ages in the low-energy spectral region, analysis of the temperature depende nce of the effective number of carriers N-eff below 0.5 eV is presented.