INFRARED REFLECTANCE OF YBA2(CU1-XNIX)3O7-DELTA FILMS

In this paper, we report the infrared reflectance R(nu,T) of a YBa2Cu3 O7-delta film in which 6% of the Cu atoms have been substituted by Ni. These spectra are taken with better resolution than in our earlier re port of films with up to 4% Ni. The reflectance spectra for the 6% Ni- doped film are very similar to those for a 4% Ni-doped film, thus conf irming our earlier conclusions about the very non-BCS gapless nature o f the optical conductivity. The new spectra make evident a plateau at R = 96% for nu < 150 cm-1 and a sharp decrease in R for nu > 150cm-1. These features imply an interesting non-Drude structure in the superco nducting density of states in the infrared.