Analysis of fluctuation conductivity in Y1−хCdxBa2Cu3O7−δ (x = 0−0.4)

Abstract

The effect that the partial substitution of Cd for Y has on the mechanism of excess conductivity formation in polycrystalline Y1−хCdxBa2Cu3O7−δ with x = 0 (Y1), 0.1 (Y2), 0.3 (Y3), and 0.4 (Y4) is investigated. The resistivity ρ of the samples increases markedly with increasing x, and the critical temperature of the superconducting (SC) state transition, Tc, decreases. The mechanism responsible for the formation of fluctuation conductivity, σ'(T), is considered within the framework of the Aslamazov–Larkin theory near Tc. The Ginzburg temperature (TG), the critical temperature in the mean-field approximation (Tcmf), the temperature of the 3D–2D crossover (T0), and T01, which limits the region of the SC fluctuations from above, are determined. It is shown that doping with Cd at x = 0−0.4 increases the coherence length along the c axis, ξc(0), by 2.7 times, and the distance between the CuO2 planes, d01, by 2.2 times. The temperature dependences of the pseudogap (PG), Δ*(T), are determined by analyzing the excess conductivity within the framework of the local pair model. It is found that with an increase in substitution, the maximum value of the PG Δ*(Tpair) decreases from 250.2 to 215.7 K, while the real value of the PG, measured at TG,Δ*(TG), increases from 217.4 to 224.2 K.

Impact of Heat Treatments and Hole Density (p) on the Structural, Electrical, and Superconducting Properties of LnSrBaCu<sub>3</sub>O<sub>6+z</sub> (Ln = Eu, Sm, Nd) Compounds

“…The linear relationship between resistivity and temperature is a widely observed characteristic in cuprates [30] [31] [32]. These electric coefficients are specific to the Cu(2)O 2 planes and are influenced by hole doping, as shown in Figure 9(a).…”

Analysis of fluctuation conductivity in Y-=SUB=-0.5-=/SUB=-Cd-=SUB=-0.5-=/SUB=-Ba-=SUB=-2-=/SUB=-Cu-=SUB=-3-=/SUB=-O-=SUB=-7-delta-=/SUB=-

“…In HTSC near T c , the coherence length along the c axis is greater than the corresponding YBCO lattice cell size d = c = 11.7 Å [33], and fluctuation superconducting pairs (FSCP) interact in the entire volume of the superconductor. Accordingly, this is the region of 3D fluctuations.…”

“…Earlier in [33] we analyzed the fluctuation conductivity in the compositions Y 1−x Cd x Ba 2 Cu 3 O 7−δ (x = 0−0.4). In the present work, the studies of the normal state of YBa 2 Cu 3 O 7−δ (Y1) and Y 0.5 Cd 0.5 Ba 2 Cu 3 O 7−δ (Y2) in the temperature range T * > T > T c , in order to determine their physical characteristics, as well as to identify the opportunity of the appearance of a PG state in the composition of Y 0.5 Cd 0.5 Ba 2 Cu 3 O 7−δ .…”