κ−(BEDT−TTF)2Cu[N(CN)2]Br: A Fully Gapped Strong-Coupling Superconductor

High-resolution specific-heat measurements of the organic superconductor $\kappa -\left(\mathrm{BEDT}-\mathrm{TTF}{)}_2-\mathrm{Cu}\right[\mathrm{N}\left(\mathrm{CN}{)}_2\right]\mathrm{Br}$ in the superconducting ( $B=0\mathrm{}$) and normal ( $B=14\mathrm{}\mathrm{T}$) states show a clearly resolvable anomaly at $T_c=11.5\mathrm{}\mathrm{K}$ and an electronic contribution, $C_{\mathrm{es}}$, which can be reasonably well described by strong-coupling BCS theory. Most importantly, $C_{\mathrm{es}}$ vanishes exponentially in the superconducting state which gives evidence for a fully gapped order parameter.