  A linear temperature dependence of the electrical resistivity as T -> 0 is
the hallmark of quantum criticality in heavy-fermion metals and the archetypal
normal-state property of high-Tc superconductors, yet in both cases it remains
unexplained. We report a linear resistivity on the border of spin-density-wave
order in the organic superconductor (TMTSF)2X (X = PF6, ClO4), whose strength
scales with the superconducting temperature Tc. This scaling, also present in
the pnictide superconductors, reveals an intimate connection between linear-T
scattering and pairing, shown by renormalization group theory to arise from
antiferromagnetic fluctuations, enhanced by the interference of superconducting
correlations. Our results suggest that linear resistivity in general may be a
consequence of such interference and pairing in overdoped high-Tc cuprates is
driven by antiferromagnetic fluctuations, as in organic and pnictide
superconductors.
