Fizika Nizkikh Temperatur: Volume 46, Number 9 (September 2020), p. 1068-1077    ( to contents , go back )

Analysis of fluctuation conductivity in Y1–хСdxBa2Cu3O7–δ (x = 0–0.4)

V. M. Aliyev, R. I. Selim-zade

G.M Abdullayev Institute of Physics of Azerbaijan NAS, Baku, 1143, Azerbaijan
E-mail: v_aliev@bk.ru

J. A. Ragimov

Azerbaijan Medical University, Baku, 1022, Azerbaijan

L. V. Omelchenko, and E. V. Petrenko

B. Verkin Institute for Low Temperature Physics and Engineering of the National Academy of Sciences of Ukraine Kharkiv 61103, Ukraine

Received December 13, 2019, revised May 12, published online July 22, 2020

Abstract

The effect of partial substitution of Y on Cd on the mechanism of excess conductivity in Y1–хCdxBa2Cu3O7–δ polycrystals with c x = 0, 0.1, 0.3 and 0.4 (samples Y1, Y2, Y3 and Y4) has been studied. With an increase in x, the resistivity of the samples ρ increased markedly, and the critical temperature of the transition to the superconducting (SC) state, Tc, decreased. The mechanism of the formation of fluctuation conductivity σ′(T) near Tc was considered in the framework of the Aslamazov–Larkin theory. The Ginzburg temperature (TG), the critical temperature in the mean-field approximation (Tcmf), the 3D–2D crossover temperature (T0), and the temperature T01, which limits the region of the SC fluctuations from above, were determined. It was shown that doping with Cd leads to an increase in the coherence length along the c axis, ξс(0), by 2.7 times, and also the distance between the CuO2 planes, d01, by 2.2 times, with an increase in x from 0 to 0.4. In the framework of the local pair model, from the analysis of excess conductivity, the temperature dependence of the pseudogap (PG), Δ*(Т), was determined. It was found that with increasing substitution, the maximum value of PG, Δ*(Tpair), decreases from 250.2 K to 215.7 K, while the real value of PG, measured at ТG, Δ*(TG), increases from 217.4 K to 224.2 K.

Key words: superconductivity, pseudogap, fluctuation conduc-tivity, coherence length, Y1–хСdxBa2Cu3O7–δ.

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