Gap symmetry of organic superconductor κ-(MDT-TTF)2AuI2 determined by specific heat

We have made precise measurement of specific heat C of the organic superconductor, (MDT-TTF)2AuI2 (Tc = 4.15 K) at low temperatures down to 0.5 K at zero field and at several fields up to 1 T. Owing to the lattice softness, the specific heat, which does not follow simple Debye T3 law, is dominant over electronic part. Subtracting the lattice part, we clarified the specific heat jump at Tc and determined the temperature dependence below Tc with the special interest of the mechanism of the superconductivity in this material. We found that the difference of C between superconducting and normal state follows the temperature dependence of the BCS framework. This is consistent with the conclusion of the previous 1H-NMR study.