Fluctuation conductivity in the superconducting compound Bi1.7Pb0.3Sr2Ca2Cu3Oy
V.M. Aliev, J.A. Ragimov, R.I. Selim-zade, S.Z. Damirova, and B.A. Tairov
Institute of Physics of Azerbaijan National Academy of Sciences, Baku Az-1143, Azerbaijan
Received March 20, 2017, revised Jule 17, 2017
The influence of the partial substitution of Bi by Pb on the mechanism of excess conductivity in the Bi–Sr–Ca–Cu–O system is studied. It was found that partial substitution of Bi for Pb leads to an increase in the critical temperatures of the sample Bi1.7Pb0.3Sr2Ca2Cu3Oу (B2) in comparison with Bi2Sr2CaCu2Ox (B1) (Tc(B2) = = 100.09 K and Tc (B1) = 90,5 K, respectively). Simultaneously, the resistivity ρ of Bi1.7Pb0.3Sr2Ca2Cu3Oу in the normal state decreases and is a factor of ≈ 1.5 smaller than that found for Bi2Sr2CaCu2Ox. The mechanism of formation of excess conductivity in cuprate HTSC Bi2Sr2CaCu2Ox and Bi1.7Pb0.3Sr2Ca2Cu3Oу was considered within the framework of the local pair model with allowance for the Aslamazov–Larkin theory near Tc. The temperature T0 of the transition from the 2D fluctuation region to the 3D region (i.e., the temperature of the 2D–3D crossover) is determined. The values of the coherence length ξс(0) along the c axis of the fluctuating cooper pairs are calculated. It is shown that the partial substitution of Bi for Pb in the Bi–Sr–Ca–Cu–O system leads to a 1,3-fold decrease in ξс(0) (4.205 and 3.254 Å, respectively), and also to shrinking of both the region of the pseudogap existence, and the region of superconducting fluctuations near Tc. The temperature dependence of the pseudogap Δ*(Т) and the value of Δ*(Tc) are determined, and the temperatures Тm, corresponding to the maximum on temperature dependences of pseudogap in these materials, are estimated. The maximum value of the pseudogap in the samples Bi2Sr2CaCu2Ox and Bi1.7Pb0.3Sr2Ca2Cu3Oу is found to be 61.06 and 38.18 meV, respectively.