Dimensional exponents of Gaussian and critical fluctuations in Bi2Sr2CaCu2O+8+δ processed under different conditions

The Gaussian and critical fluctuations of quenched and furnace cooled samples are studied to find out the nature of fluctuations above and below the mean field critical temperature respectively. The fluctuation induced conductivity of the polycrystalline Bi-2212 sample is extracted. The processing conditions of a superconductor affect the fluctuation conductivity. The variation of dimensional exponent (λ)with the reduction in temperature is not sharp but a continuous phenomenon over a temperature range. The variation of λ in the furnace cooled sample is unlike that in the quenched sample. The fluctuation induced conductivity below the mean field critical temperature is extracted to study the nature of the dimensional exponent in the paracoherence region. (author)