Thermodynamic behavior of the 10 K class organic superconductor κ-(BEDT-TTF)2Cu(NCS)2 studied by relaxation calorimetry

Heat capacities of single crystal of κ-(BEDT-TTF)2Cu(NCS)2, which is known as an organic superconductor with Tc = 9.5 K, were measured with a recently constructed 3He-calorimeter of a relaxation type. A large heat capacity jump of about ΔCpT−1 = 65 mJ K−2 mol−1 was observed in association with the superconductive transition. The characteristic behavior of the thermal anomaly is compared with the previous results reported. Only slight change was found between the heat capacity peaks for the slowly cooled and rapidly cooled samples. This demonstrates that the degree of disorder left in the cooling process is not so serious in this material.