Abstract
We report on the optical properties of undoped single crystal the parent compound of the colossal magnetoresistive manganites. Near-normal-incidence-reflectance measurements are reported in the frequency range of and in the temperature range The optical conductivity is derived by performing a Kramers-Kronig analysis of the reflectance data. The far-infrared spectrum of displays the infrared active optical phonons. While several of the phonons soften as the temperature is raised, no anomalies in the width or frequency of the phonons are observed at the Neel temperature of the sample The high-frequency is characterized by the onset of absorption near 1.5 eV, a peak at 2 eV, and a second larger peak at 4 eV. The 2-eV feature has been identified as optical transitions across the Jahn-Teller split levels. The spectral weight of this feature increases in the low-temperature state. This implies a transfer of spectral weight from the UV to the visible region associated with the paramagnetic to antiferromagnetic state. We discuss the results in terms of the double-exchange processes that affect the optical processes in this magnetic material.
- Received 29 March 2001
DOI:https://doi.org/10.1103/PhysRevB.64.224426
©2001 American Physical Society