The quantum spin liquid state based on the quasi-isotropic triangular system in EtMe3Sb[Pd(dmit)2]2 was greatly interested in due to its peculiar quantum character. Our recent heat capacity measurements of this compound discovered the interesting characters such as gap-less excitations. However, the character of this compound still has open question. In this study, we have performed heat capacity measurement for deuterated quantum spin liquid compound Et(CD3)3Sb[Pd(dmit)2]2 in order to explore the effect of deuteration. As a result we found two peculiar behaviors in deuterated sample. One is suppression of large heat capacity below 1 K. This result suggests the origin of large heat capacity in pristine sample due to proton rotation of Me group in cation layer. The other observation is anomalous increase of electronic heat capacity at low temperatures. Possibility of electronic structure change by chemical pressure is expected as a kind of quantum behavior in spin liquid state.
Fig.1. The temperature dependence of CpT -1 of the pristine sample (EtMe3Sb[Pd(dmit)2]2: red square) and the deuterated sample (Et(CD3)3Sb[Pd(dmit)2]2: light green circle). The high value of CpT -1 seen in the pristine sample was suppressed in the deuterated sample.
Fig.2. TheCpT -1 vs T 2 plot of the pristine sample (EtMe3Sb[Pd(dmit)2]2) and the deuterated sample (Et(CD3)3Sb[Pd(dmit)2]2). In spite of similar behavior of heat capacities higher than 2 K (4 K2), the significant difference was observed below this temperature. This difference considered as due to anomalous enhancement of electronic heat capacity related to quantum critical behavior.