Infrared studies of a<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mrow><mml:msub><mml:mrow><mml:mi mathvariant="normal">La</mml:mi></mml:mrow><mml:mrow><mml:mn>0.67</mml:mn></mml:mrow></mml:msub></mml:mrow><mml:mrow><mml:msub><mml:mrow><mml:mi mathvariant="normal">Ca</mml:mi></mml:mrow><mml:mrow><mml:mn>0.33</mml:mn></mml:mrow></mml:msub></mml:mrow><mml:mrow><mml:msub><mml:mrow><mml:mi mathvariant="normal">MnO</mml:mi></mml:mrow><mml:mrow><mml:mn>3</mml:mn></mml:mrow></mml:msub></mml:mrow></mml:math>single 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 $(20--9000{\mathrm{cm}}^{\mathrm{\ensuremath{-}}1}).$ The optical conductivity gradually changes from a Drude-like behavior to a broad peak feature near $5000{\mathrm{cm}}^{\mathrm{\ensuremath{-}}1}$ in the ferromagnetic state below the Curie temperature ${T}_{C}=307\mathrm{K}.$ 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 ${T}_{C}.$