Gapless Spin Excitations
in the Triangular Spin System
Consists of Deuterated BEDT-TTF

Heat capacity measurements of organic triangular lattice compound κ-(BEDT-TTF)2Cu2(CN)3 were performed to discuss the low energy excitations from the spin-liquid ground states. Concerning on the sample of which hydrogen atoms in ethylene group in BEDT-TTF molecule have been substituted by deuterons, we have observed almost similar thermodynamic behavior as the hydrogenated sample. The absence of drastic change of electronic properties of this compound is consistent with the electronic phase diagram given by Kurosaki et al. (Phys. Rev. Lett. 95, 17001(2005)). The obtained data are well consistent with the previous heat capacity experiments. The existence of the γ term demonstrates that the excitations from the quantum spin liquid states show a gapless behavior at least down to 0.7 K.

(by S. Yamashita & T. Yamamoto)

	Fig. 1. The schematic figure of BEDT–TTF molecules. The hydrogen atoms in ethylene group in BEDT–TTF molecule have been substituted by deuterons.
	Fig. 2. CpT −1 vs T2 plot of hydrogenated κ–(BEDT–TTF)2Cu2(CN)3 samples and a deuterated sample. There is no considerable difference in heat capacities between hydrogenated sample and deuterated sample.
	Fig. 3. CpT −1 vs T2 plot of the deuterated κ–(BEDT–TTF)2Cu2(CN)3 sample obtained in a temperature range between 0.8 K and 7 K.