Thermodynamic Measurements of Quantum Spin Liquid Material Performed by the Micro-Chip Device

We have constructed a micro-chip calorimeter to measure heat capacity of quite small crystals of organic conductors. Using the calorimeter, we have measured heat capacity of κ-(BEDT-TTF)2Cu2(CN)3 and its deuterated one both of which show quantum spin liquid state, where BEDT-TTF is an abbreviation of bis(ethylenedithio)tetrathiafulvalene. The thermal anomaly in κ-(BEDT-TTF)2Cu2(CN)3 was observed by the chip calorimeter. We have investigated effects of magnetic fields against the broad anomaly around 6 K by changing magnitude and directions in the donor layer. It does not show any difference when the external field of 7 T were applied from various directions in the 2D plane. Similar tendency was observed in deuterated κ-(BEDT-TTF)2Cu2(CN)3.

(by Y. Muraoka & Y. Nakazawa)

	Fig.1. Molecular structures of BEDT–TTF and deuterated BEDT–TTF.
	Fig.2. Temperature dependence of heat capacity of κ–(h8–BEDT–TTF)2Cu2(CN)3 around 6 K obtained under 0 T and 7 T. The thermal anomaly around 6 K does not show any angular dependence in magnetic field direction.
	Fig.3. Temperature dependence of heat capacity of κ–(d8–BEDT–TTF)2Cu2(CN)3 around 6 K obtained under 0 T and 7 T. The overall tendency is identical with that of h8–sample.