ELECTRONIC AND 2-MAGNON LIGHT-SCATTERING IN OXIDE SUPERCONDUCTING CRYSTALS

From investigations of two-magnon Raman scattering (RS) under high pre ssures up to 430 kbar in Eu2CuO4 and YBa2Cu3O6.2 crystals, it was show n that the dependence of the superexchange integral i on the distance between Cu and O atoms in CuO2 planes a is anomalously weak (J is-prop ortional-to a(-n), n=3+/-0.5). The large value of J indicates strong i nitial overlapping of Cu and O wave functions in high-T(c) materials. It was found that an increase in free carrier concentration results in a rapid increase of magnon damping and the disappearance of the two-m agnon peak from RS spectra. A detailed study of electron Raman scatter ing has been carried out in superconducting and insulating Y Ba2Cu3O6x single crystals. The spectral redistribution at frequencies omega < 600 cm-1 in different polarizations indicate that the superconducting gap is strongly anisotropic. In the normal (metallic) phase the behavi or of the imaginary part of the response function R''(omega) in the po larization (x'x') corresponds to the model of a marginal Fermi liquid, and in the polarization (x'y'), this behavior is independent of the t emperature. In insulating crystals, R''(omega) is independent of tempe rature to T greater than or similar to 200 K in both polarizations.