Comparative resistivity studies under hydrostatic pressure on different variants of the organic superconductor κ - (ET)₂Cu[N(CN)₂]Br

Resistivity measurements on four samples of κ - (ET)₂Cu[N(CN)₂]Br, synthesized by following two different preparation routes, yield strongly sample-dependent ρ(T) profiles. By comparing the interlayer resistivities and their response to hydrostatic pressure we infer: (i) a significant part of the inelastic-scattering contribution, causing the anomalous ρ(T) maximum around 90K, is extrinsic in nature, (ii) the abrupt change in the slope of ρ (T) around T* ≈ 40K is sample independent and most likely marks a second-order phase transition, (iii) the origin of the ρ(T) ∝ AT² dependence at low temperatures, with a strongly sample dependent coefficient A and range of validity, is different from coherent Fermi-liquid excitations.