Infrared studies of aLa0.67Ca0.33MnO3single crystal: Optical magnetoconductivity in a half-metallic ferromagnet

The infrared reflectivity of a ${\mathrm{La}}_{0.67}{\mathrm{Ca}}_{0.33}{\mathrm{MnO}}_3$ single crystal is studied over a broad range of temperatures (78–340 K), magnetic fields (0–16 T), and wave numbers $(20\mathrm{}–9000{\mathrm{cm}}^{\mathrm{-}1}).\mathrm{}$ The optical conductivity gradually changes from a Drude-like behavior to a broad peak feature near $5000{\mathrm{cm}}^{\mathrm{-}1}$ in the ferromagnetic state below the Curie temperature $T_C=307\mathrm{}\mathrm{K}.$ Various features of the optical conductivity bear striking resemblance to recent theoretical predictions based on the interplay between the double exchange interaction and the Jahn-Teller electron-phonon coupling. A large optical magnetoconductivity is observed near $T_C.$