Heat Capacity Measurements
of an Organic Superconductor
κ-[(BEDT-TTF)1−x (BEDSe-TTF)x]2-
Cu[N(CN)2]Br under Pressures

Thermodynamic properties of an organic superconductor of κ-[(BEDT-TTF)1−x(BEDSe-TTF)x]2Cu[N(CN)2]Br (x ~ 0.1) have been studied by the ac-modulation technique under pressures and with magnetic fields. The superconductive transition temperature of x = 0 salt (11.6 K) shifts to lower temperature with the increase of x. Over x ~ 0.33, the superconductivity is suppressed. Using the high-pressure calorimetry cell, we have observed a thermal anomaly around 6 K at ambient pressure. The suppression of the superconductivity by magnetic fields suggests that the observed peak is associated with the superconductive transition. Upon pressurize to 3 kbar, a thermal anomaly related to the superconductive transition was observed around 4.7 K. The decrease of transition temperature Tc suggests that the superconductive phase has suppressed by applying the pressure.

(by N. Tokoro & Y. Nakazawa)

	Fig. 1. CpT-1 vs T plot of κ–[(BEDT–TTF)1−x(BEDSe–TTF)x]2Cu[N(CN)2]Br (x ~ 0.1) at ambient pressure. A thermal anomaly related to the superconducting phase transition is observed around 6 K. The critical temperature shows a downward shift with the increase of magnetic fields.
	Fig. 2. CpT-1 vs T plot of κ–[(BEDT–TTF)1−x(BEDSe–TTF)x]2Cu[N(CN)2]Br (x ~ 0.1) under pressure of 3 kbar. We can see a thermal anomaly related to the superconducting phase transition around 4.7 K. The downward shift of critical temperatures by magnetic fields is also observed.