Magnetic and electronic phase diagram and superconductivity in the organic superconductorsκ−(ET)2X

The magnetic susceptibility of the organic superconductors $\kappa -(\mathrm{h}8\mathrm{}\mathrm{}or\mathrm{}\mathrm{d}8-\mathrm{E}\mathrm{T}{)}_{2}X,$ $X=\mathrm{Cu}(\mathrm{NCS}{)}_2$ and $\mathrm{Cu}\left[\mathrm{N}\right(\mathrm{CN}{)}_2]\mathrm{Br}$ has been studied. A metallic phase below $T^{*}=37\mathrm{}–38\hspace{0.5em}\mathrm{K}$ for $X=\mathrm{Cu}\left[\mathrm{N}\right(\mathrm{CN}{)}_2]\mathrm{Br}$ and 46–50 K for $X=\mathrm{Cu}(\mathrm{NCS}{)}_2$ has an anisotropic temperature dependence of the susceptibility and the charge transport. Partial charge-density-wave or charge fluctuation is expected to coexist with the metallic phase instead of the large antiferromagnetic fluctuation above $T^{*}.$ The phase diagram and the superconductivity of $\kappa -(\mathrm{ET}{)}_{2}X$ are discussed in connection with this phase.