Effect of impurity and radiation defects on the scattering of normal and fluctuation carriers in YBa2Cu3O7–δ and Y1–zPrzBa2Cu3O7–δ single crystals

Abstract

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.