Infrared Studies of a La_{0.67}Ca_{0.33}MnO_3 Single Crystal: Optical   Magnetoconductivity in a Half-Metallic Ferromagnet
  The infrared reflectivity of a $\rm La_{0.67}Ca_{0.33}MnO_3$ single crystal is studied over a broad range of temperatures (78-340 K), magnetic fields (0-16 T), and wavenumbers (20-9000 cm$^{-1}$). The optical conductivity gradually changes from a Drude-like behavior to a broad peak feature near 5000 cm$^{-1}$ in the ferromagnetic state below the Curie temperature $T_C=307 K$. 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 $T_C$. 
A. V. Boris, N. N. Kovaleva, A. V. Bazhenov, P. J. M. van Bentum, Th.   Rasing, S-W. Cheong, A. V. Samoilov, N.-C. Yeh