Excess conductivity of Pb-doped (Cu0.5−xPbxTl0.5)Ba2Ca2Cu3O10−δ superconductors

Abstract The excess conductivity was determined from the resistivity measurements of the as-prepared and oxygen annealed (Cu 0.5− x Pb x Tl 0.5 )Ba 2 Ca 2 Cu 3 O 10− δ ( x  = 0, 0.15, 0.25, 0.35) samples in the temperature region well above the superconducting transition temperature. The excess conductivity data was analyzed in the light of Aslamazov–Larkin (AL) theory and its modified form given by Lawrence–Doniach (LD) model. These analyses have shown that the excess conductivity data of (Cu 0.5− x Pb x Tl 0.5 )-1223 samples fits very well to the two-dimensional (2D) and three-dimensional (3D) AL equations. Moreover, at higher temperature a crossover from 2D to 0D was also observed. The width of 3D region has been increased; but, the increase was not monotonous. However, the width of 0D region has been increased up to x  = 0.25. The zero temperature coherence length [ ξ c (0)] has shown a decreasing trend with the increase of T c (0) and Pb concentration in the charge reservoir layer (Cu 0.5− x Pb x Tl 0.5 )Ba 2 O 4− δ . The phase relaxation time [ τ ϕ ] and coupling parameter λ obtained from FIC analysis shows that the fluctuation pairs are formed both due to electron–phonon and electron–electron correlations in (Cu 0.5− x Pb x Tl 0.5 )-1223 samples. The (Cu 0.5− x Pb x Tl 0.5 )-1223 samples were also annealed in oxygen to change the carrier concentration in the CuO 2 planes. A possibility of suppression of the spin and charge density gaps with Pb-doping is also discussed.