Fluctuation-induced conductivity and dimensionality in polysulfur nitride

Abstract

Polymeric sulfur nitride, ${(\mathrm{SN})}_{x}$ is found to exhibit, well above its superconducting transition temperature, electrical conductivity in excess of the normal-state conductivity. This effect is shown to be attributable to thermodynamic fluctuations. The magnitude and the temperature dependence of the effect agree with the predictions of the Aslamazov and Larkin theory for fluctuation-induced conductivity in systems which are either one dimensional (1-D) or zero dimensional (0-D) with respect to the superconducting coherence length; the 1-D or 0-D behavior depending on the sample. Since the overall dimensions of the samples are very much greater than the ${(\mathrm{SN})}_{x}$ coherence length, this behavior is interpreted as due to weak coupling between 1-D or 0-D particles which form bulk (3-D) conglomerates. From an analysis of the temperature-dependent fluctuation conductivity, it is determined that the cross-sectional diameter of these elongated particles is certainly greater than five times the polymer interchain distance and most likely has an average value of 250 \AA{}. The particle lengths are strongly related to sample quality (as measured by dc resistivity) and have an average value of a few thousand angstroms.