Probing the order parameter of the layered organic superconductorκ−(BEDT−TTF)2Cu[N(CN)2]Brby ac susceptibility measurements

Ac susceptibility measurements are reported for single crystals of the layered organic superconductor $\kappa {-(\mathrm{B}\mathrm{E}\mathrm{D}\mathrm{T}-\mathrm{T}\mathrm{T}\mathrm{F})\mathrm{}}_2\mathrm{Cu}\left[\mathrm{N}\right(\mathrm{CN}{)}_2]\mathrm{Br}.$ The value of the out-of-plane penetration depth ${\lambda }_b\mathrm{}\left(0\right)\mathrm{}$ was found to be 133 $\mu \mathrm{m},$ consistent with earlier results. The temperature dependence of the in-plane superfluid density, with the value of in-plane component ${\lambda }_{\mathrm{ac}}\mathrm{}\left(0\right)\mathrm{}$ of the order of 1 $\mu \mathrm{m},$ is strongly linear in T, whereas the out-of-plane superfluid density varies as $T^2$ at low temperatures. The observed behavior is fully consistent with the one expected for d-wave superconductivity.