Single Crystal Heat Capacity Measurement of Charge Glass Compound θ-(BEDT-TTF)2CsZn(SCN)4 Performed under Current and Voltage Application

Heat capacity measurements of θ-(BEDT-TTF)2CsZn(SCN)4 in its non-equilibrium electronic states induced by applying electric currents and voltages were performed by a modified relaxation calorimetry technique. We developed a single crystal heat capacity measurements system by which the Joule heating produced in samples by external currents and voltages can be balanced with the cooling power to make a non-equilibrium steady state. Although temperature versus time profiles in the relaxation process in calorimetry can be obtained as exponential curves as in the usual relaxation technique, we found that the change of resistivity that occurs during the heating and relaxation process should be taken into account in analyzing the data. By correcting this factor in the analyses, we succeeded in evaluating absolute values of Cp(I) and Cp(V) in these non-equilibrium states. The experiments up to 150 μA and the constant voltage of 20 mV do not induce visible change in the structure of the Boson peak in CpT−3 vs. T suggestive of the glassy ground state of phonons. Although the suppression of the short-range fluctuations of the charge density has been reported, it does not seriously affect the glassy phonons in this current range.

The effect of lattice disorder on the low-temperature heat capacity of (U1−yThy)O2 and 238Pu-doped UO2

The low-temperature heat capacity of (U1−yThy)O2 and 238Pu-doped UO2 samples were determined using hybrid adiabatic relaxation calorimetry. Results of the investigated systems revealed the presence of the magnetic transition specific for UO2 in all three intermediate compositions of the uranium-thorium dioxide (y = 0.05, 0.09 and 0.12) and in the 238Pu-doped UO2 around 25 K. The magnetic behaviour of UO2 exposed to the high alpha dose from the 238Pu isotope was studied over time and it was found that 1.6% 238Pu affects the magnetic transition substantially, even after short period of time after annealing. In both systems the antiferromagnetic transition changes intensity, shape and Néel temperature with increasing Th-content and radiation dose, respectively, related to the increasing disorder on the crystal lattice resulting from substitution and defect creation.

Development of light irradiation calorimetry system for molecule-based compounds

Construction of a calorimetry system, by which the light irradiation to the surface area of molecular crystals at extremely low temperatures can be possible is reported. The development was performed based on the relaxation calorimetry technique to evaluate electronic structure using small amount of samples of molecular compounds where the electron correlation effects and electron–lattice coupling effects induce drastic change of the ground state. Detection of electronic structure changes occur as the light-induced phenomena becomes possible by this type of calorimetry apparatus. We report on the detailed structure of the small-sized calorimetry cells constructed for this purpose as well as the design of the calorimeter. The experimental results using organic superconductor and magnetic materials are given, which substantiate that the absolute value measurements under light irradiation are promising using the developed systems. Further possibility is also discussed.