FINE-STRUCTURE OF THE INFRARED REFLECTION SPECTRA IN YBA2CU3O6+X SINGLE-CRYSTALS

In the far-infrared region the reflection spectra for the E perpendicular-to C and E parallel-to C polarizations in YBa2Cu3O6+x single crystals of the various oxygen content are studied. It is found that in the superconducting state the fine structure of the E perpendicular-to C polarization spectra including the features at 150-250 and 480 cm-1 can be explained by normal free carriers scattering with optical phonons and by the direct excitation of optical phonons. Studying the temperature behavior of the optical phonon frequencies shows the presence of two superconducting gaps in the crystal of T(c)=80 K: the gap with 5.0<2DELTA(t)/kT(c)<5.6 in the CuO2-plane carrier spectrum the gap 2DELTA2/kT(c) almost-equal-to 2 may be related to the chain carriers. The experimental results are interpreted in the framework of the SNS-structure of superconducting YBa2Cu3O6+x.