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The effect of medium fluences (from 1019 е/cm2 to 1020 е/cm2) of fast electron irradiation or the change in the praseodymium concentration in the range 0.0 ≤ z ≤ 0.5 on the excess conductivity of optimally oxygen-doped YBa2Cu3O7–δ single crystals has been investigated. Irradiation leads to the appearance of a significant number of defects that cause a decrease in anisotropy, an appreciable increase in phonon scattering, reduction of Tc, and broadening of the superconducting transition. Under the conditions specified, the temperature dependence of electrical resistivity is approximated with high accuracy by the charge carriers' scattering on defects and phonons, and fluctuating conductivity in the Lawrence–Doniach model. It was determined that at fluences 0 ≤ Ф ≤ 6.5⋅1019 е/cm2, the value of the transverse coherence length ξс(0) increases with an increase of Ф by about three times or more than four times as the content of praseodymium in the sample increases to z ≈ 0.42. In both cases, the 2D–3D crossover point shifts upward in temperature. In contrast to the case of irradiation with low fluences (Ф ≤ 1019 е/cm2) or doping with praseodymium up to concentrations z ≤ 0.39, irradiation with medium fluences and doping with praseodymium at higher concentrations leads to a nonmonotonic dependence of the transverse coherence length ξс(0) on the irradiation fluence, with characteristic maxima at Ф ∼ (7–8)⋅1019 е/cm2 or z ≈ 0.42, which may be due to the general suppression of the superconducting characteristics. [ABSTRACT FROM AUTHOR]

The effect of medium doses (from 1019 to 1020 cm–2) of irradiation with fast electrons (energy, E = 2.5 MeV) on the excess conductivity of optimally doped Y1Ba2Cu3O7–δ single crystals has been studied. It is shown that the irradiation with electrons leads to the significant expansion of the temperature interval for the existence of excess conductivity, thereby narrowing the region of the ρ(T) linear dependence in the ab plane in the normal state. It has been established that at doses of 0 ≤ D ≤ 6.5⋅1019 cm–2, the value of the transverse coherence length ξc(0) increases with D by about 3 times and the 2D–3D crossover point shifts in temperature. In contrast to the case of irradiation with low doses (D ≤ 1019 cm–2), irradiation with medium doses leads to a nonmonotonic dependence of the transverse coherence length ξc(0) on the irradiation dose, with a characteristic maximum at D ∼ (7–8)⋅1019 cm–2, which may be related to the general suppression of superconducting characteristics. [ABSTRACT FROM AUTHOR]

The temperature dependences of the longitudinal and transverse conductivity of YВа2Сu3О7−δ single crystals irradiated with high-energy electrons were measured. It was found that, in contrast to unexposed YВа2Сu3О7−δ single crystals, the absolute value of the electrical resistivity anisotropy ρc/ρab significantly decreases with an increase in the number of structural defects in the experimental sample volume. The dependence ρc/ρab(Т) is well described both by the universal "1/2 law" and by the usual exponential expression for thermally activated conductivity. [ABSTRACT FROM AUTHOR]

The effect of room-temperature annealing on the basal-plane conductivity of YBCO single crystals is investigated after their irradiation with fast electrons. It is revealed that the excess conductivity Δ σ (T) of the samples obeys an exponential temperature dependence in a broad temperature range T f < T < T ∗ . Here, T f is the crossover temperature from the pseudogap to the fluctuation conductivity regime. The description of the excess conductivity with the expression Δ σ ∝ T / T ∗ exp (Δ ∗ / T) can be interpreted in terms of the mean-field theory where T ∗ corresponds to the mean-field transition temperature to the pseudogap state and the dependence Δ σ (T) is described within the framework of the BCS-BEC crossover theory. [ABSTRACT FROM AUTHOR]

Temperature dependences of the electrical resistance along the c-axis of YBa 2 Cu 3 O 7 − δ single crystals are investigated before and after irradiation with electrons at 0.5–2.5 MeV energies. The irradiation was done at T ≲ 1 0  K and the irradiation dose was varied from 1. 4 × 1 0 1 8   cm − 2 to 8. 8 × 1 0 1 8   cm − 2 . An enhancement of the charge carriers localization with increase of the irradiation dose has been revealed. A crossover from the pseudogap (PG) regime to the variable-range hopping conductivity has been observed. [ABSTRACT FROM AUTHOR]

The effect of irradiation with high-energy electrons on the transverse electrical resistivity of YBa2Cu3O7–δ single crystals with a high degree of perfection that are optimally doped with oxygen is considered. This irradiation creates macroscopic regions oriented along the layers in the sample, which are characterized by oxygen deficiency, leading to variable-range hopping transverse conductivity. An increase in the dose of irradiation leads to a decrease in the region of localization of charge carriers. [ABSTRACT FROM AUTHOR]

Evolution of the excess conductivity in optimally doped YBa 2 Cu 3 O 7 - δ single crystals is investigated after their irradiation with fast electrons at T ≲ 10 K at energies of 0.5–2.5 MeV and a dose of 3 × 10 18 cm - 2 . The measurements were performed in a magnetic field of 15 kOe applied at various angles with respect to the basal plane of the crystals. The temperature dependences of the paraconductivity were analyzed within the framework of the Aslamazov–Larkin theoretical model of fluctuation conductivity and revealed two major effects of the electron irradiation. Namely, (i) the vortex-lattice-melting kinks in the resistivity temperature dependences vanish after electron irradiation and (ii) the resistivity data in the irradiated state allow for a Kouvel-Fisher-type scaling pointing to the presence of a irradiation-induced vortex Bragg-glass phase. These effects are discussed in terms of a competition between intrinsic pinning due to point defects and volume pinning induced by electron irradiation. In all, our findings are relevant for YBCO-based circuitry which is exposed to fast electrons in moderately strong magnetic fields. [ABSTRACT FROM AUTHOR]

Irradiation with electrons is an efficient approach to induce a large number of defects with minimal impact on the material composition. In high-temperature superconducting cuprates, electrons with MeV energies produce point defects in the form of interstitial ions and vacancies that act as efficient scattering centers. Here, we analyze the changes in the electronic transport along the c-axis of YBa2Cu3O7-δ single crystals after their irradiation with 0.5-2.5 MeV electrons at T≲10 K and a dose of 1018 cm-2. While a variable-range hopping conductivity associated with some mesoscopic length scale is observed in the non-irradiated samples, we reveal a two-step superconducting transition in the irradiated samples, that attests to the presence of an additional, macroscopic inhomogeneity induced by the electron irradiation. [ABSTRACT FROM AUTHOR]

It is shown that electron irradiation leads to the appearance of macroscopic (comparable with the sample thickness) fluctuations in the sample composition, which coexist with mesoscopic fluctuations. A decrease in Тс caused by a change in the oxygen deficiency and/or the appearance of displaced Cu, Y, and Ba atoms, was also detected. A resistance minimum is observed in the normal state, which shifts toward high temperatures after irradiation. [ABSTRACT FROM AUTHOR]

Irradiation with electrons is an efficient approach to inducing a large number of defects with a minimal impact on the material itself. Analysis of the energy transfer from an accelerated particle smashing into the crystal lattice shows that only electrons with MeV energies produce point defects in the form of interstitial ions and vacancies that form perfect scattering centers. Here, we investigate the changes in the resistive characteristics of YBCO single crystals from the 1-2-3 system after several steps of low-temperature irradiation with 0.5-2.5 MeV electrons and irradiation doses of up to 8.8×1018 cm-2. The penetration depth of such electrons is much larger than the crystal thickness. We reveal that defects appearing in consequence of such electron irradiation not only increase the residual resistance, but they affect the phonon spectrum of the system and lower the superconducting transition temperature linearly with increase of the irradiation dose. Furthermore, the irradiation-induced defects are distributed non-uniformly, that manifests itself via a broadening of the superconducting transition. Interestingly, the excess conductivity remains almost unaffected after such electron irradiation. [ABSTRACT FROM AUTHOR]

In this work, the evolution of the excess conductivity of the YВа2Сu3О7−δ single crystals under electron irradiation is studied. It is shown that irradiation with electrons leads to a significant expansion of the temperature interval that excess conductivity exists. Therefore, the value of the transverse coherence length ξс(0) increases by a factor of 1.4 and the point of the 2D-3D crossover shifts with respect to the temperature. [ABSTRACT FROM AUTHOR]

The effect of electron irradiation at T ≲ 10 K (energy 0.5–2.5 MeV, dose 1018 cm–2) on the parameters of charge carrier scattering and superconducting transition characteristics in an optimally doped Y–Ba–Cu–O single crystal (Тc = 91.74 K) was studied. Irradiation with electrons leads to a significant increase in the residual resistance and the Debye temperature. The latter is associated with the isotropization of the phonon spectrum due to an increase in the concentration of defects. Irradiation also results in a decrease in Тc and an increase in the coherence length. [ABSTRACT FROM AUTHOR]