Evolution of over-conductivity of YВа₂Сu₃О₇-δ single crystals under the exposure of irradiation by high-energy electrons

The evolution of the excess conductivity of YВа₂Сu₃О₇-δ single crystals upon electron irradiation is investigated. It was shown that electron irradiation leads to a significant expansion of the temperature range for the existence of excess conductivity, thereby narrowing the region of the linear dependence of p(Т) in the ab plane. It was found that the excess conductivity Δσ(Т) of YВа₂Сu₃О₇-δ single crystals in a wide temperature range Tf<Т<T⚹ (Тf – the transition temperature from the PG to the FP mode) is subject to exponential temperature dependence. Moreover, the description of excess conductivity using the relation Δσ ⁓ (1-Т/Т⚹)exp(Δ⚹ab/T) (Δ⚹ab – the pseudogap in ab-plane) can be interpreted in terms of the mean-field theory, where T⚹ is presented as the mean-field temperature of the transition to the PG state, and the temperature dependence of the pseudogap is satisfactorily described in the framework of the BCS-BEC crossover theory. In this case, the value of the transverse coherence length ξс(0) increases 1.4 times and the 2D-3D crossover point shifts in temperature.Досліджено еволюцію надлишкової провідності монокристалів YВа₂Сu₃О₇-δ при опроміненні електронами. Показано, що опромінення електронами призводить до значного розширення температурного інтервалу існування надлишкової провідності, тим самим, звужуючи область лінійної залежності p(Т) в ab площині. Встановлено, що надлишкова провідність Δσ(Т) монокристалів YВа₂Сu₃О₇-δ в широкому інтервалі температур Tf<Т<T⚹ підпорядковується експоненційній температурній залежності. При цьому опис надлишкової провідності за допомогою співвідношення Δσ⁓(1–Т/Т⚹)exp(Δ⚹ab/T) може бути інтерпретовано в термінах теорії середнього поля, де Т⚹ представлена, як середньополева температура переходу в ПЩ-стан, а температурна залежність псевдощілини задовільно описується в рамках теорії кросовера БКШ-БЕК. При цьому величина поперечної довжини когерентності ξс(0) збільшується в 1,4 рази, і зміщується по температурі точка 2D-3D кросовера.Исследована эволюция избыточной проводимости монокристаллов YВа₂Сu₃О₇-δ при облучении электронами. Показано, что облучение электронами приводит к значительному расширению температурного интервала существования избыточной проводимости, тем самым, сужая область линейной зависимости p(Т) в ab-плоскости. Установлено, что избыточная проводимость Δσ(Т) монокристаллов YВа₂Сu₃О₇-δ в широком интервале температур Tf<Т<T⚹ подчиняется экспоненциальной температурной зависимости. При этом описание избыточной проводимости с помощью соотношения Δσ⁓(1–Т/Т⚹)exp(Δ⚹ab/T) может быть интерпретировано в терминах теории среднего поля, где Т⚹ представлена, как среднеполевая температура перехода в ПЩ-состояние, а температурная зависимость псевдощели удовлетворительно описывается в рамках теории кроссовера БКШ-БЭК. При этом величина поперечной длины когерентности ξс(0) увеличивается в 1,4, раза и смещается по температуре точка 2D-3D кроссовера

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

Scattering of electrons in oxygen underdoped YBa₂Cu₃O₇₋x single crystals

The electrical resistivity in the range of Tc-300 K in the layer planes of YBa₂Cu₃O₇₋x single crystals with a range of oxygen deficiency, which is characterized by the Tc in the range 78 + 92 K was studied. The experimental data on the resistance in normal state are approximated by an expression that takes into account the scattering of electrons on phonons, as well as on defects and the fluctuation conductivity in 3D-model of the Aslamazov-Larkin theory. According to this approximation, depending upon the oxygen deficiency, the Debye temperature changes from 245 to 400 K, coherence length ξc(0) ≈ 0.5 Å

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

Effect of electron irradiation on excess conductivity of single Y₁Ba₂Cu₃O₇₋δ crystals

Effect of electron irradiation on the excess conductivity of Y₁Ba₂Cu₃O₇₋δ single crystals is investigated. It is shown that irradiation with electrons leads to significant expansion of the temperature interval that excess conductivity exists. The excess conductivity Δσ(T) has been revealed to obey an exponential temperature dependence in he broad temperature range Tf < T < T*. The description of the excess conductivity can be interpreted in terms of the mean-field theory where T* is the mean-field ransition temperature to the pseudogap state and Δ*(T) is satisfactory described within the framework of the BCS-BEC crossover heory. The value of the transverse coherence length ξc(0) increases by a factor of 1.4 and the point of 2D-3D crossover shifts with respect to temperature

Effect of high pressure on conductivity in the basal plane of Y₁₋xPrxBa₂Cu₃O₇₋δ single crystals lightly doped of praseodymium

Effect of high hydrostatic pressure up to 17 kbar on conductivity of lightly Pr-doped Y₁₋xPrxBa₂Cu₃O₇₋δ (x~0.05) single crystals is investigated. We show that in contrast to non-doped YBa2Cu3O7-δ samples, application of the high pressure leads to a substantial increase of the pressure derivative of the coherence length dξc/dP and temperature shift of 2D-3D crossover point. Possible mechanisms of the influence of the high pressure on the critical temperature and the coherence length are discussed within the frames of a model assuming the presence of singularities in the charge carriers electron spectrum typical for lattices with strong coupling. The excess conductivity Δ σ(T) inY₀.₉₅xPr₀Ba₂Cu₃O₇₋δ has beenY0.95Pr0.05Ba2Cu3O7-δ revealed to obey an exponential dependence in the wide temperature range Tf < T < T*. At this, description of the excess conductivity by the expression Δ σ ~ (1 - T/T*)exp(Δ*ab/T) can be interpreted in terms of the mean-field theory, where T* is the mean-field superconducting transition temperature and pseudogap temperature dependence is satisfactory described within the framework of the BCS-BEC crossover theory. An increase of the applied pressure leads to narrowing of the temperature range of realization of the pseudogap regime, thereby expanding the linear temperature dependence of the basal-plane resistivity ρab(T)