Optical reflectivity studies of magnetically oriented YBa_2Cu_3O_7−δ

The optical reflectivity spectra of magnetically oriented YBa2Cu3O7 −δ are reported over a wide energy range from 50 to 24 000 cm−1 (6 meV to 3 eV). A strong optical anisotropy is observed, with most phonon modes associated with the E ‖ c spectrum. An anisotropic effective-medium theory is used to permit direct comparison of these data with spectra from unoriented grains. The excitonic feature is found to be considerably more intense in the unoriented sample.