A. V. Kuznetsov

Magnetic flux creep in HTSC films

In weak magnetic fields, precision measurements of the magnetic moment relaxation in thin epitaxial films YBa2Cu3O7−δ are performed. The exponents µ of the dependence of the vortex motion activation energy on the current are determined in a wide temperature range. Despite the low vortex density, the data obtained indicate the collective nature of their creep, which is probably caused by the strong interaction of vortices through the space surrounding the film.

An interplay between spatially separated Fermi and Bose subsystems and superconductivity in perovskite-like oxides

Abstract A new scenario for the insulator-metal phase transition and the superconductivity in the perovskite-like bismuthates Ba1−xKxBiO3 (BKBO) based on our EXAFS-studies is proposed. We have shown that two types of the charge carriers: the local pairs (real-space bosons) and the itinerant electrons exist in the metallic Ba1−xKxBiO3 (x⩾0.37). Bosons and fermions occupy different types of the octahedral BiO6 complexes, so they are separated in real space. A new type of spatially separated Fermi–Bose mixture is likely to be realized in bismuthates. The likeness of the local peculiarities of BiO6 complexes in bismuthates and CuOn complexes in cuprates allows one to discuss the applicability of this scenario for all high-Tc perovskite-like oxides. A new superconducting oxide Ba1−xLaxPbO3 has been successfully synthesized to check our conclusions.

The peculiarities of local structure of YbNi2 and YbCo2 intermetallics synthesized at high pressure.

Local structure of YbCo2 and YbNi2 was investigated by EXAFS and XANES spectroscopy. It was found that the bond Yb-Co(Ni) has the highest static disorder and its length increases with temperature decrease, while all other bonds remain almost unchanged. This phenomenon may be caused by short-range magnetic ordering at temperatures above the phase transition. XANES measurements above ZIII-Yb absorption edge in YbCo2 and YbNi2 revealed that both compounds have almost the same density of free 5d-states

Local lattice distortions and the nature of superconductivity in Ba(K)BiO3-BaPb(Bi)O3

Based on the temperature dependent XAFS- studies of bismuthates BaPb1−xBixO3(BPBO) and Ba1−xKxBiO3(BKBO) the model of the relationship of the local crystal and the local electronic structures have been proposed. We found that it is the local structure distortions that are mostly responsible for the main macroscopic properties of these compounds. The proposed model explains the long list of contradictions observed in transport measurements, inelastic neutron and electron scattering, UPS, XPS, EXAFS and Raman spectroscopy of the BPBO-BKBO systems. The likeness of the local peculiarities of BiO6 and CuOn complexes allows us to hope that similar approach can be applied to the copper-based superconductors.