FAR-INFRARED CONDUCTIVITY OF YBA//2CU//3O//7//-//Y.

The authors review experimental data on the optical conductivity of YBa//2Cu//3O//7//-//y. Kramers-Kronig analysis shows that in the mid-infrared range the optical conductivity is typical of perovskites with a rich phonon structure in the oxygen bond stretching-and-bending region. In the far-infrared range, a depression of conductivity sets in below the superconducting transition temperature that is associated with the presence of a superconducting energy gap. In all the samples that have been looked at there is residual conductivity in the gap.