Thermal anomaly around the superconductive transition of κ-(BEDT-TTF)2Cu(NCS)2 with external pressure and magnetic field control

Abstract

The temperature dependence of the ac heat capacity of a molecule-based superconductor κ-(BEDT-TTF)2Cu(NCS)2 under external pressures and with magnetic fields is reported. A peak structure in C p T −1 due to the superconductive transition was observed around 9 K at ambient pressure. This peak is suppressed by applying magnetic fields up to 7 T. The systematic decrease in the transition temperature with the increase in external pressure is confirmed by thermodynamic measurements under 0.15, 0.30 and 0.45 GPa. Through the analysis of the peak shape of the thermal anomaly, it is suggested that the gradual suppression of the coupling strength of the superconductivity occurs with the increase in pressure. This feature is consistent with the argument based on the chemical pressure effect in the superconductive phase of κ-(BEDT-TTF)2 X system, where X denotes mono-valence counter anions. The result demonstrates that the appearance of the Fermi-liquid character produced by applying pressure in the dimer-Mott phase diagram affects the nature and the coupling feature of the superconductivity. Importance of high-pressure heat capacity for molecule-based compounds is emphasized.