Thermodynamics of the quantum spin liquid state of the single-component dimer Mott system κ-H3(Cat-EDT-TTF)2

Thermodynamic properties of the proton-mediated single component dimer-Mott insulator of kappa-H-3(Cat-EDT-TTF)(2), which has a two-dimensional triangle lattice structure of S = 1/2 spins, are reported. The extraordinary large electronic heat capacity coefficient gamma= 58.8 mJK(-2) mol(-1) observed by the low-temperature heat capacity measurements up to 6 T suggests the formation of the gapless spin liquid ground state. Although the magnetic interaction J/k(B) is quite different from those of other dimer-Mott spin liquids, the thermodynamic feature scales well with the Wilson ratio of 1.4-1.6. The heat capacity measurements also detected that the deuteration of the proton-linkage changes the ground state to the nonmagnetic one with almost vanishing.. Using the data of the deuterated compound, the accurate temperature dependence of the magnetic heat capacity reflecting on the low-energy excitations from the gapless spin liquids ground state is discussed.