Sample-dependent resistivity profiles in K-(ET)₂Cu[N(CN)₂]Br organic superconductors - interrelations with other normal- and superconducting-state properties

The organic superconductor κ-(ET)₂Cu[N(CN)₂Br shows striking sample-to-sample variations in the electrical resistivity [1]: While most of the crystals reveal a ρ(T) maximum around 90 K with a semiconducting behaviour above, some remain metallic for T < 300 K. In the absence of significant differences in the crystals´structural parameters, chemical composition and ESR spectra, these results indicate that real structure phenomena, i.e. disorder and/or defects, strongly affect the inclastic scattering. [1]. Here we report on a comparative resistivity study on a variety of crystals with quite different ρ(T) profiles. The work aims at seeking out interrelations between the anomalous scattering contributions at intermediate temperatures and features of the normal- and superconducting-state, susch as the glass transition at T₉ ≈ 77 K, the temperature T* ≈ 40 K [1], as well as the superconducting transition temperature. [1] C. Strack et al., Phys. Rev. B 72 054511 (2005)