Construction of a thermal conductivity measurement system for small single crystals of organic conductors

We newly constructed a thermal conductivity measurement system for single crystals of molecular compounds. This system enables us to measure the thermal conductivity of samples with the length of less than 1.0 mm. In order to evaluate the capability of detection of phase transitions occurred in molecule-based materials, we performed the thermal conductivity measurement of single crystals of organic conductors α-(BEDT-TTF)2I3 and κ-(BEDT-TTF)2Cu[N(CN)2]Br, where BEDT-TTF denotes bis(ethylenedithio)tetrathiafulvalene. From the temperature dependence of the thermal conductivity of α-(BEDT-TTF)2I3, we succeeded in observing the metal–insulator transition as a sudden drop of κ(T) at 135 K. In the temperature dependence of thermal conductivity of κ-(BEDT-TTF)2Cu[N(CN)2]Br, we could observe the increment of κ(T) at the metal-superconducting transition (Tc = 11.4 K). These results show that the newly developed system has high performance enough to detect various kinds of phase transitions in small crystals of molecular compounds.