Many organic superconductors have low-dimensional character in theirs electric states. Accurate configuration and ideal horizontality of a sample against magnetic fields is required when we intend to obtain a piece of in-plane information. One of the important information for understanding superconductivity is in-plane anisotropy of electric heat capacities. However, angle dependence of electric heat capacities is usually extremely small as compared with the total heat capacity and quasiparticle excitation of perpendicular field component is concealed. Therefore, it is requested to measure heat capacity with quite high sensitivity and with accurate control within ideal horizontal control. We tried to develop a calorimeter to cover these demands and assessed performance of the new developed calorimeter. As a result, we attained enough resolution measurement accuracy the electric heat capacity within horizontal control of magnetic fields to guarantee angle-resolved measurements. Consequently, we detected a sign of the fourfold symmetry and angle dependence of in-plane electric anisotropy of κ-(BEDT-TTF)2Cu(NCS)2. For understanding more detailed angle dependence that is related to quasiparticle excitation by in-plane field, systematic studies for various superconductive materials are necessary.
Fig.1 A comparison of temperature dependence of blank heat capacity of the present cell and the previous one reported in annual report in 2012.
Fig.2 Angle dependence of heat capacity of κ-(BEDT-TTF)2Cu(NCS)2 in the bc plane. The magnetic field direction control can allow anisotropy measurements in a superconducting mixed state of organic superconductors.