Thermodynamic measurements of doped dimer-Mott organic superconductor under pressure

Thermal anomalies in the temperature dependence of the heat capacity around the superconducting transition of a hole-doped superconductor, κ−(BEDT-TTF)₄Hg_2.89Br₈, which is known as a dimer-Mott triangle lattice system are investigated by the ac modulation technique under external pressure. To detect the electronic phase transition under applied pressure conditions for a single crystal sample, we have improved resolution of the ac modulation technique. By tracking the appropriate frequency during the temperature scan measurement, we succeed in detecting the thermal anomaly with the applied pressure of 0.3 GPa where the electronic state is located in the crossover region of non-Fermi liquid to Fermi liquid. Application of the external magnetic fields of H = 2 and 6 T in the in-plane direction reveals that the superconductivity in this doped triangle lattice of molecular dimers is relatively stable against the magnetic field. (author)