Normal and oblique specular reflectivity ofCuGeO3

We report on the ac-plane specular reflectivity of ${\mathrm{CuGeO}}_3$ as a function of the angle of incidence. While our spectra for near-normal incidence are those of an insulator, in the grazing-incident spectrum we found a broad continuum. This suggests that the b-direction response, that is, the response normal to the ac plane, is weakly metallic. We suggest the origin of this electronic anisotropy is due to impurity levels in the gap. We reason that its presence is due to oxygen vacancies in the chains and that this would justify, at least in part, some of the softening of the longitudinal acoustical mode recently reported by neutron-scattering measurements.