Fluctuation conductivity in cuprate superconductors

Abstract

We have measured the in-plane resistivity of Bi 2 Sr 2 CaCu 2 O 8+δ and Tl 2 Ba 2 CaCu 2 O 8+δ single crystals in the temperature range 70-300 K. The thermodynamic fluctuations in the conductivity of both the samples start around ∼ 125 K. We find the Lawrence and Doniach [1] model to be inadequate to describe the fluctuation conductivity in these materials. The modification suggested by Ramallo et al [4] where by the conductivity is enhanced due to the presence of two superconducting layers in each unit cell is also not adequate. We suggest the fluctuation conductivity to be reduced due to the reduction in the density of states (DOS) of the quasiparticles which results due to the formation of Cooper pairs at the onset of the fluctuations. The data agrees with the theory proposed by Dorin et al [5] which takes into account this reduction in DOS.