Ruslan V. Vovk

c-axis hopping conductivity in heavily Pr-doped YBCO single crystals

We investigated the temperature dependence of the longitudinal and transverse conductivity of Y1−zPrzBa2Cu3O7−δ single crystals with different praseodymium contents. The correlation between the experimental results and the predictions of various theoretical models was analyzed. It is observed that the increase of the praseodymium concentration in Y1−zPrzBa2Cu3O7−δ single crystals leads to increased localization effects and suppression of the superconducting state. Interestingly, for single crystals with large praseodymium content the anisotropy of the normal electrical resistivity ρc/ρab(T) is described by the universal ‘law of 1/2’ for thermally activated hopping conductivity. This is in contrast to the case for comparable crystals of YBa2Cu3O7−δ.

Interactions between phonon sheets in superfluid helium

We have measured the effect of colliding two phonon sheets together at different angles. At small angles they interact strongly and a hot line is formed along the line of intersection of the two sheets. At angles between ~13? and ~27? the interaction becomes weaker and less energy goes into the hot line. At angles greater than ~27? there is no interaction between the sheets and they pass through each other. By delaying one sheet with respect to the other, the path of the hot line can be shifted laterally. Using this behaviour, we show that the sensitive area of the bolometer is around 10?2?mm2. We have measured the profile of the hot line and find that its width, typically 1?mm, varies as 1/sin(?/2), where ? is the angle between the two sheets. We analyse the data and estimate that the typical angle between two phonons interacting by the three phonon process varies between 8.4? and 12.5?, depending on their energy. We model the formation of the hot line when the sheets are strongly interacting. From the model and the measured data, we find that the temperature of the hot line decreases, and the cone angle and energy density of the hot line increases, with both increasing energy density in the sheets and increasing angle ?.

Temperature dependence of the pseudogap in aluminum and praseodymium-doped YBa2Cu3O7-δ single crystals

Abstract We have investigated the conductivity in the basis plane of YBaCuO single crystals slightly doped by Al and Pr with a pre-specified topology of twin boundaries. The excess conductivity for the analyzed samples shows dependence Δ σ ∼ ( 1 - T / T * ) exp ( Δ ab * / T ) in a wide temperature range T f T T * , where T * is the mean field temperature of superconducting transition. The temperature dependence of the pseudogap can be satisfactorily described in terms of the BCS–BEC crossover theoretical model.In present work the conductivity in the basis plane of YBaCuO single crystals slightly doped by Al and Pr with a pre-specified topology of twin boundaries has been investigated. The excess conductivity for the analyzed samples shows dependence like

INFLUENCE OF LONGITUDINAL MAGNETIC FIELD ON THE FLUCTUATION CONDUCTIVITY IN SLIGHTLY Al-DOPED YBa2Cu3-zAlzO7-δ SINGLE CRYSTALS WITH A GIVEN TOPOLOGY OF PLANE DEFECTS

\Delta\sigma\sim(1-T/T^*)\exp(\Delta_{ab}^*/T)

INFLUENCE OF HIGH PRESSURE ON THE TEMPERATURE-DEPENDENCE OF THE PSEUDO-GAP IN OXYGEN DEFICIENT YBa2Cu3O7-δ SINGLE CRYSTALS

in wide temperature range

Phase segregation and the effect of high pressure on the electro-transport in Y0.95Pr0.05Ba2Cu3O7-δ single crystals

T_f<T<T^*

Mobile fluxons as coherent probes of periodic pinning in superconductors

, where

Conductivity anisotropy in Y1-yPryBa2Cu3O7-δ single crystals in a wide range of praseodymium concentrations

T^*

Zero-Bias Shapiro Steps in Asymmetric Pinning Nanolandscapes

can be represents as mean field temperature of superconducting transition. The temperature dependence of pseudogap can be satisfactory described in terms of the BCS-BEC crossover theoretical model.

Oxygen self-diffusion in apatites

In this work we study the influence of the constant magnetic field up to 14 kOe to the temperature dependence of the electrical conductivity in the ab-plane of aluminium doped YBa2Cu3O7-δ single crystals with an unidirectional twin boundaries system. The temperature dependence of the excess para-conductivity is interpreted within the Aslamazov–Larkin theoretical model of the fluctuation conductivity. It was shown that the lack of fan-shaped expansion of the resistive transitions in the magnetic field in these samples may be due to the lack of the non-pinning vortex liquid phase.