Effect of high-pressure-induced structural relaxation on evolution of the temperature dependence pseudogap in HoBa2Cu3O7-δ single crystals

In present work the influence of high pressure on the conductivity in the basal plane of the oxygen underdoped HoBa2Cu3O7-δ single crystals is investigated. It is found that excess conductivity Δ(Т) in the HoBa2Cu3O7-δ single crystals over a wide temperature range (Tс<Т<T*, where Tc is the critical temperature and T* represents the mean field temperature of the superconducting transition) obeys an exponential temperature dependence. The description of the excess conductivity with Δ~(1-Т/Т*)exp(Δ*ab/T) can be interpreted in terms of mean field theory. The temperature dependence pseudogap is satisfactorily described within the framework of the BCS-BEC crossover. В роботі досліджено вплив високого тиску на провідність в базисній площині ВТНП-монокристалів HoBa2Cu3O7-δ з нестачею кисню. Встановлено, що надлишкова провідність (Т) монокристалів HoBa2Cu3O7-δ у широкому інтервалі температур Tс<Т<T* підкоряється експоненційній температурній залежності. При цьому описання надлишкової провідності за допомогою співвідношення Δ~(1-Т/Т*)exp(Δ*ab/T) може бути інтерпретовано в термінах теорії середнього поля, де Т * представлена, як середньопольова температура надпровідного переходу, а температурна залежність псевдощілини задовільно описується в рамках теорії кросовера БКШ-БЕК. В работе исследовано влияние высокого давления на проводимость в базисной плоскости ВТНП-монокристаллов HoBa2Cu3O7-δ с недостатком кислорода. Установлено, что избыточная проводимость (Т) монокристаллов HoBa2Cu3O7-δ в широком интервале температур Tс<Т<T* подчиняется экспоненциальной температурной зависимости. При этом описание избыточной проводимости с помощью соотношения Δ~(1-Т/Т*)exp(Δ*ab/T) может быть интерпретировано в терминах теории среднего поля, где Т* представлена, как среднеполевая температура сверхпроводящего перехода, а температурная зависимость псевдощели удовлетворительно описывается в рамках теории кроссовера БКШ-БЭК

Про створення лінгвосоціокультурного адаптаційного центру для іноземних громадян

The necessity of creation of the lingualsocial-cultural adaptation centre for foreigners is substantiated in the article. The components of the adaptation process are analyzed. The main directions of the activity of the centre are considered.У статті обґрунтовується необхідність створення центру лінгвосоціокультурної адаптації для іноземних громадян, аналізуються складові процесу адаптації, розглядаються основні напрямки роботи адаптаційного центру

Evolution of normal electrical resistance in oxygen underdoped Ho₁Ba₂Cu₃O₇₋δ single crystals in the process of application-removal of high hydrostatic pressure

The influence of high hydrostatic pressure on electrical resistance in afr-plane of oxygen underdoped Ho₁Ba₂Cu₃O₇₋δ has been studied. It was found that high-pressure-in-duced redistribution of labile oxygen leaded to increasing phase separation, which was accompanied by a process of structural relaxation and uphill diffusion in the bulk of the pilot sample. It has been suggested that the generation of low-temperature (oxygen-depleted) phase can occur at twin boundaries. The temperature dependence of the resistivity above Tc can be accurately approximated by the model s-d-electron scattering by phonons. Application of high pressure leads to a decrease of the resistance, which at high temperatures is much larger than at low temperatures. This may be due to the weakening the electron-phonon interaction with increasing pressure

Aging-effect in optimal doped Yba₂Cu₃O₇₋δ single crystals

We investigate the conducting properties of the optimally oxygen doped YBa₂Cu₃O₇₋δ single crystals in the basal ab-plane before and after a long time exposure (aging) at air atmosphere. Prolonged exposure leads to increase of amount of the effective scattering centers of the normal carriers. The excess conductivity in a wide temperature range has exponential temperature dependence and near the critical temperature (Tc) is well described within the Aslamazov-Larkin theoretical model. Here we show that the prolonged exposure leads to a great extention of temperature range of the pseudogap state implementation and to narrowing the linear section of the dependence ρab(T)

Anisotropy of magnetoresistance in untwinned YBa₂Cu₃O₇₋δ single crystals

In this work we study an influence of the disorientation angle between direction of constant magnetic field up to 15 kOe and ah-plane α ≡ ∠(H,ab) on the temperature dependences of the excess conductivity in the temperature interval of transition to superconducting state in untwinned YBa₂CU₃O₇₋δ single crystals with a small oxygen hypostoichiometry. At temperature T > Tc, the temperature dependence of the excess para-conductivity is interpreted within the Aslamazov-Larkin theoretical model of the fluctuation conductivity for layered superconductors. The cause of appearances of low temperature "tails" (para-coherent transitions) on the resistive transitions, corresponding to different phase regimes of the vortex-matter state is discussed. Remove selecte

Transverse resistance in HoBa2Cu3O7−δ single crystals

The transverse electrical resistance of HoBa2Cu3O[Formula: see text] single crystals is investigated in the temperature range [Formula: see text] for optimally-doped [Formula: see text] and oxygen-poor [Formula: see text] samples. With decreasing temperature, the resistivity of the optimally-doped samples has been found to transit from the regime of scattering on phonons and defects to the regime of “semiconductor” character and, near [Formula: see text], of the fluctuation conductivity. The oxygen-poor samples have been revealed to exhibit only a variable range hopping conductivity of “semiconductor” character, which near [Formula: see text] transits into the fluctuation conductivity. A significant anisotropy of the residual resistivity and characteristics of the fluctuation conductivity is observed for samples of both types.</jats:p

Effect of transverse and longitudinal magnetic field on the excess conductivity of YBa₂Cu₃₋zAlzO₇₋δ single crystals with a given topology of plane defects

The effect of a constant magnetic field to 12.7 kOe on the temperature dependences of electric conductivity of aluminum-doped YBaCuO single crystals with a system of unidirectional twinning boundaries has been investigated. It is determined that the twinning boundaries are effective centers of scattering of fluctuation carriers. Directly near Tc the temperature dependences of the excess paraconductivity are satisfactorily described by the Hikami-Larkin theoretical model of fluctuation conductivity for layered superconducting systems. The reasons for the suppression of three-dimensional superconducting fluctuations and the nonmonotonic dependence of ξc(0,H) in weak magnetic fields with the magnetic field vector oriented along c axis were discussed. It was shown that the lack of fan-shaped expansion of the resistive transitions in the magnetic field in these samples is conditioned by the lack of the no pinning vortex liquid phase due to increased pinning of the vortex lattice at the twin boundaries