THE EFFECT OF PRESSURE ON THE SCATTERING OF NORMAL AND FLUCTUATION CARRIERS IN Y0.66Pr0.34Ba2Cu3O7−δ SINGLE CRYSTALS

Abstract

The experimentally obtained temperature dependences of the electrical resistance, ρ(T), of the single-crystal high-temperature superconductor (HTSC) Y_0.66Pr_0.34Ba₂Cu₃O_7–δ in the normal state (T* ≤ T ≤ 300 K) at different values of quasi-hydrostatic pressure     (0 ≤ P ≤ 1 GPa) are approximated by the Bloch–Grüneisen relation, which takes into account the scattering of charge carriers on phonons and defects. The temperature derivative of the resistance, dρ(Т)/dT, in the normal state passes through a maximum (T_max ≈ θ/3, θ is the Debye temperature), which fully corresponds to the model used. The presence of a high-temperature maximum dρ(Т)/dT indicates the absence of a linear dependence of the electrical resistance in the studied sample at least in the region T ≲ 300 K. The superconducting transition leads to the appearance of a low-temperature maximum at T = T_c. The temperature of the minimum between these maxima is identified with the pseudogap opening temperature T*. The latter increases with increasing hydrostatic pressure. Extrapolation of the normal conductivity (in the Bloch–Grüneisen model) to the temperature range T_c < T ≲ T* allows us to calculate the fluctuation conductivity. The fluctuation conductivity, obtained as the difference between the experimental resistance values and the values extrapolated using the Bloch – Grüneisen relation, is described with good accuracy by the Lorentz – Doniach relation, taking into account the inhomogeneity of the sample. The baric dependences of the parameters of the Lorentz – Doniach model show that hydrostatic pressure contributes to the improvement of the sample structure. The pressure-induced evolution of the fluctuation conductivity in Pr-doped Y_0.66Pr_0.34Ba₂Cu₃O_7–δ single crystals can be determined by two circumstances: an increase in the “three-dimensionality” of the system due to a change in the ratio between the coherence length ξ_c and the interlayer distance d and a shift of the Fermi level relative to the features of the density of electronic states. In contrast to undoped (or lightly Pr-doped) YBCO samples, the application of high pressure leads to a significant increase in the baric derivatives, dT_c/dP and dξ_c/dP.