EFFECT OF HIGH PRESSURE ON TEMPERATURE DEPENDENCE OF PSEUDOGAP IN Y0.66Pr0.34Ba2Cu3O7-δ SINGLE CRYSTALS

Abstract

The paper investigates the effect of high hydrostatic pressure on the conductivity, s(T), in the basic ab-plane of the HTSC single crystal Y_0.66Pr_0.34Ba₂Cu₃O_7–δ. The YBa₂Cu₃O_7–δ single crystal was grown using the well-known solution-melt technology. Y₂O₃, BaCO₃, CuО and Pr₅O₁₁ compounds were used in the appropriate percentage ratio as initial components for growing Y_0.66Pr_0.34Ba₂Cu₃O_7–δ single crystal. The modes of growth and oxygen saturation of the Y_1–xPr_xBa₂Cu₃O_7–δ crystal were the same as for undoped single crystals. Electrical resistance in the ab-plane was measured according to the standard 4-pin method. Hydrostatic pressure was created in a piston-cylinder multiplier. The temperature dependences of the specific electrical resistance, r(Т), of the studied single crystals in the ab-plane in the temperature range T_c–300 K at pressures of 0–10 kbar were obtained experimentally. At all applied pressures, the experimental curves r(T) contain linear sections at temperatures T > T*. When T < T*, the r(T) curves deviate downward from their linear extrapolation, i.e., excess conductivity, Ds(T), appears in the studied samples. It was established that Ds(T) of the samples in a wide temperature range T_f < T < T* are characterized by an exponential temperature dependence                                        Δs ~ (1–Т/Т*)exp(Δ*_ab/T), where T* is the mean-field temperature of the superconducting transition, and can be interpreted in terms of the BCS-BEC crossover theory. Using this ratio, the temperature dependence of the pseudogap, Δ*_ab(T), from T* to the temperatures corresponding to the maximum value of the pseudogap was constructed. An increase in the applied pressure leads to the effect of narrowing the temperature interval of realization of the pseudogap (PG) mode and, as a result, to the expansion of the interval of the linear dependence of the specific electrical resistance in the ab-plane. As the pressure increases, the temperature dependence of the pseudogap shows a crossover from the dependence of the BCS type to the dependence of the BEK type.