[en] Lattice vibrations of YBa₂Cu₃O_7-x crystals with a site-selective isotope substitution ¹⁸O → ¹⁶O are investigated theoretically. It is shown that shifts of the frequencies of A_1g oxygen vibrations due to this substitution are smaller than under complete one. However, phonon bands and normal vectors are changed much stronger, especially in the case when apical oxygens are substituted. On the basis of the presented analysis anharmonic properties and transition temperatures of the selectively substituted crystals are also briefly discussed. (orig.)

[en] Qualitative analysis of spectra of visible radiation Raman scattering (RS) in YBa₂Cu₃O_7-δ is conducted. Arguments supporting the decisive role of bridges connecting planes and chains in the formation of primary polarization of oxygen Ag- bands along c axis are presented

[en] Qualitative theory of light scattering on 335, 435 and 500 cm^-1 phonons in YBa₂Cu₃O_7-δ was constructed. Preliminary ZZ-polarization for 500 cm^-1 phonon, related with tridge oxygen, is explained by pronounced difference of overlap integrals of dpσ and dpπ type, where d and p-atomic orbitals of copper and oxygen. It is shown that single phonon light scattering by CuO₂-planes is resolved only due to distortions of their form and therefore can't be used for determining force of electron-phonon bond in them. Explanation of high scattering intensity on the planar 435 cm^-1 phonon in ZZ-component of the spectrum, based on participation of bridge oxygen in CuO₂-plane vibration, is suggested. High intensity of scattering on the planar 335 cm^-1 phonon in planar (xx and yy) polarizations, as compared to 435 cm^-1 phonon, testifies to fulfilment of /E/>>4t criterion, where E-difference of energies on copper and oxygen with account of electron correlations, t-integral of electron transfer. Possibilities of analyzing energy spectrum of charge carriers according to the dependence of scattering intensity on δ were discussed

[en] The binding of carriers by an external potential in the presence of a weak long-range electron-phonon coupling with longitudinal optical phonons is considered. This coupling results in a nonlocal effectively attractive contribution in the Schroedinger equation that makes the formation of a bound state possible in weaker potentials. As a physical example the potential of a charge cluster in heavily doped polar semiconductors is considered

[en] Raman scattering (RS) by coupled electron-phonon excitations in a crystal with disturbed translational symmetry (e.g. due to impurities) is investigated. Due to impurities the q=0 selection rule is broken and the phonon line shape can become asymmetric. In addition, for an anisotropic phonon dispersion, the line shape depends on the propagation direction of the phonon. It is shown that the impurity induced non-zero momentum of the phonons opens a new channel for scattering from electrons. (orig.)

[en] The resonant dependence of the light combinational scattering intensity by fully-symmetric phonons in YBa₂Cu₃O_7-x for different polarization of incident and scattered light is investigated. An analysis of the resonance profiles shows that the scattering by 435 and 500 cm^-1 phonons is a typical two-band process and is determined by the diagonal terms of the electron-phonon interaction. The connection between the Fermi energy and velocity and the shape of the resonance is discussed. The resonant dependence for 335 cm^-1 phonons is quite different. The difference is ascribed to the fact that different electron transitions give the main contribution to the Raman polarizability

[en] We report experimental results on resonant electronic Raman scattering in superconducting single crystals of Bi₂Sr₂CaCu₂O_8+x. The change of excitation wavelength results in a shift of the position for the superconductivity-induced 2Δ peak in A_1g and B_1g symmetries. In addition, in the red-light excitation a new Raman peak arises at approximately 130 K in the B_1g spectra. Various explanations of these effects are discussed. (author)

[en] The authors consider theoretically and experimentally how an extended van Hove singularity manifests itself in electronic and phonon Raman scattering in superconducting cuprates. The analysis and experimental data shows that in the case of singularity carriers redistribution between different parts of the Brillouin zone and/or electronic bands is a common feature of both the electronic and phonon Raman scattering

[en] We consider in detail Raman scattering by vibration of the apical oxygen ions in the RBa₂Cu₃O₇ superconducting cuprates. The scattering intensity is very sensitive to the ratio of diagonal and off-diagonal matrix elements of electron-phonon coupling, band structure, and carrier concentration. Our results show a large quantitative difference between the results of frozen-phonon and perturbational approach to the Raman process. The discrepancy becomes especially large when interband transitions to the states near the Fermi level are close to resonance with the incident light. The calculation of phonon-induced ion charge fluctuations shows an analogous discrepancy. The reason for these effects is the possibility of carrier redistribution between different parts of the Fermi surface arising in the frozen-phonon approximation. Our results show that Raman scattering in superconducting superlattices is very sensitive to the properties of the states near the Fermi level. For this reason experiments performed on the superlattices can help to resolve the discrepancy. (orig.)

[en] We investigate the charge redistribution in high T_c cuprates as a function of pressure, composition, and doping. To this extent we have performed first-principles calculations based on density functional theory for several representatives of the Hg based cuprates. In particular, we focus on the creation of holes in the copper-oxygen planes. Conclusions are drawn about the similarities and differences between the three parameters influencing the superconducting transition temperature. (copyright 2004 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)