We have measured the specific heat down to 1.5 K of a collection of high-quality single crystals of κ-(ET${)}_2$Cu(NCS${)}_2$ in fields parallel to the crystalline $a^{\mathrm{*}}$ direction to 12.5 T. In this first determination of γ, we find γ to be 25±3 mJ/${\mathrm{K}}^2$ mole. The anomaly in C at $T_c$ is quite distinct when compared to normal-state data obtained by suppressing $T_c$ with field. The value of ΔC/γT>2 obtained implies that this organic superconductor has strong coupling.

• Received 16 August 1989

DOI:https://doi.org/10.1103/PhysRevB.40.11345