[en] It is well known that retardation effects are essential to allow the attractive part of the electron-electron interaction (for instance, phonon mediated) to overcome the Coulomb repulsion. In new superconductors such as the cuprates for which the interaction is a priori unknown, it is therefore essential to determine the retarded and non retarded parts of the interaction. We show how this can be achieved by an analysis of Sharvin contact measurements between a noble metal tip and a cuprate. It turns out that both the retarded and non retarded parts are large, the former being however larger than the later

[en] We investigate the changes of the total energy, the electronic bands, and the dielectric function with the displacement of the apical oxygen position in YBa₂Cu₃O₇ by LAPW-calculations. From these data we calculate the corresponding vibronic Raman-spectrum. Anharmonic terms of the vibrational potential and higher order derivatives of the dielectric function are taken into account. We find excellent agreement with experimental data for the phonon frequency as well as for the intensities of fundamental and overtone spectra within a wide temperature range

[en] Using pulsed Raman spectroscopy, we directly examined the intrinsic apical O potential in insulating YBa₂Cu₃O_6.25 and metallic YBa₂Cu₃O_6.9. We selectively excited the apical O vibration mode with ultra short laser pulses to obtain a 'hot' apical O vibration mode in a 'cold' bulk phonon background. Measurements showed that the apical O phonon frequency shift and linewidth change are much smaller in the case of selective heating of the apical O vibration mode compared to bulk heating. The results agree well with theoretical predictions and indicate a strong influence of surrounding lattice ions on the apical O potential. (author)

[en] The response of point contacts between tantalum, copper or niobium and YBa₂Cu₃O_7-δ ceramics to microwave and optical electromagnetic radiation is studied. The ceramics inhomogeneous composition requires the effect of radiation on the circuit resistive elements be taken into account, particularly at high biases

[en] Possibility of high-temperature superconductivity in high-correlated systems of 3d- and 2-p-electrons with orbital degeneration is studied on the basis of kinematic mechanism. Phase diagrams of models of HTS oxides with e_g²-electrons are calculated

[en] The flux creep rate at 77.3 K for the fields below 2000 Oe, and the relation between flux creep rate and temperature for the fields of 150, 300 Oe have been experimentally studied in Bi(Pb) SrCaCuO bulk superconductor. The flux pinning potential U₀ is estimated. There is a decrease of flux pinning potential U₀ with the increase of temperature above 77.3 K in a certain field

[en] The samples of YBa_2-xSr_xCu₃O_7-δ (x = 0.000, 0.299) were prepared. Their superconducting transition temperatures (Tc) were measured. The results show that Tc decreases when Sr atoms substitute for Ba atoms partially in the sample. Their crystal structures have been measured by neutron diffraction method, with their oxygen defect values (δ) being obtained. The reason for the decrease of Tc is discussed primarily from these experimental results

[en] The movements of the flux lines in the YBa₂Cu₃O_7-δ epitaxial film have been studied by Hall effect and the broadening of the resistance-temperature curves(R-T curves) in the magnetic field. From the broadened R_T curves the exponent relation is obtained between the value of the activation energy of the flux creep and the value of the field. From the measurements of the Hall coefficient R_H the unusual variation of the Hall coefficient corresponding to the broadening of the R-T curves is found. All of the variations in the R-T curves as well as the R_H-H curves have been also discussed by the vortex glass model, exploring the laws of the flux creep in different ways

[en] The microstructure of BiSrCaCuO superconductor has been studied. Bi₂Sr₂Ca₂Cu₃O_y phase with T_c = 110 K and Bi₂Sr₂CaCu₂O_y phase with T_c = 80 K are existed in the samples. The T_c of superconductor depends on the proportion and the distribution state of the two phases. Pb dopping is benificial to the formation and stabilization of high T_C phase. The sintering process influences the microstructure of the superconductivity of the samples

[en] The analysis of a previous paper, in which it was shown that the energy for the Aharonov-Bohm effect could be traced to the interaction energy between the magnetic field of the electron and the background magnetic field, is extended to cover the case in which the magnetic field of the electron is shielded from the background magnetic field by a superconducting material. The paradox that arises from the fact that such a shielding would apparently preclude the possibility of an interaction energy is resolved and, within the limits of the ideal situation considered, the observed experimental result is derived. 7 refs