Fluctuation induced conductivity in the Sn-doped (Bi, Pb)2Sr2Ca2Cu3Oy superconducting system

The resistivity data above the transition temperatures of the systems Bi1.7Pb0.3Sr2Ca2Cu3.6Oy, Bi1.7Pb0.3Sn0.05Sr2Ca2Cu3.55Oy and Bi1.6Pb0.4SnxSr2Ca2Cu3Oy (x = 0, 0.05 and 0.10) have been studied. The excess conductivity above the transition temperature shows a power law behaviour. The Sn-free samples have an exponent λ ∝ 1.0, confirming that superconducting fluctuations in this system have a two-dimensional nature and a coherence length of 13.2 A. There is an increase in the exponent in the Sn-doped samples. This is interpreted as evidence that there is a disorder which breaks the homogeneity of the superconducting fluctuations in the Cu-O planes, with the fluctuations developing an effective dimensionality between one and two. (orig.)