Magnetic properties and superconducting-fluctuation diamagnetism above Tc in Bi2−xPbxSr2CaCu2O8+δ (x=0.0, 0.1, 0.2, 0.3, 0.5) and Bi2−xPbxSr2Ca2Cu3O10+δ (x=0.2, 0.25)

Abstract

The magnetic susceptibilities χ(T) of the title compounds above and below Tc are reported. For the Bi2−xPbxSr2CaCu2O8+δ (Bi 2:2:1:2) system, optimization of the phase purity and superconducting properties is found between x=0.2 and 0.3. The χ(T) data for these Bi 2:2:1:2 and for the two Bi 2:2:2:3 samples increase monotonically with temperature from Tc up to at least 400 K, exhibiting strong negative curvature below ∼200 K. From theoretical fits to the data in the two-dimensional regime above Tc using the static Lawrence-Doniach model as modified by Klemm, we conclude that the negative curvature in χ(T) for each sample arises from superconducting-fluctuation diamagnetism (SFD). The data are thus consistent with a superconducting order parameter of s-wave symmetry. From the fits to the data, the Ginzburg-Landau coherence lengths in the CuO2 planes were obtained and found to be ξab(0)=20.4(2) Å for Bi 2:2:1:2 and 11.8(4) Å for Bi 2:2:2:3. The value for Bi 2:2:1:2 is comparable to those calculated from upper critical magnetic-field data for this compound (23.5–27.1 Å). Our ξab(0) values for Bi 2:2:1:2 and Bi 2:2:2:3 are also comparable with that (13.6 Å) found from our previous similar analysis of the SFD in YBa2Cu3O7. The possible role of the bridging oxygens out of the CuO2 plane in Bi 2:2:2:3 and the influence of the dynamics in the fits to the SFD in the Bi-based compounds remain to be addressed.

Source-reported materials — not catalogue approval

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