Thermodynamics of the quantum spin liquid state of the single-component dimer Mott system κ − H 3 ( Cat − EDT − TTF ) 2

Thermodynamic properties of the proton-mediated single component dimer-Mott insulator of $\ensuremath{\kappa}\text{\ensuremath{-}}{\mathrm{H}}_{3}{(\mathrm{Cat}\text{\ensuremath{-}}\mathrm{EDT}\text{\ensuremath{-}}\mathrm{TTF})}_{2}$, which has a two-dimensional triangle lattice structure of $S=1/2$ spins, are reported. The extraordinary large electronic heat capacity coefficient $\ensuremath{\gamma}\phantom{\rule{0.16em}{0ex}}=\phantom{\rule{0.16em}{0ex}}58.8\phantom{\rule{0.28em}{0ex}}\mathrm{mJ}\phantom{\rule{0.16em}{0ex}}{\mathrm{K}}^{\ensuremath{-}2}\phantom{\rule{0.16em}{0ex}}\mathrm{mo}{\mathrm{l}}^{\ensuremath{-}1}$ 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 $J/{k}_{\mathrm{B}}$ is quite different from those of other dimer-Mott spin liquids, the thermodynamic feature scales well with the Wilson ratio of 1.4\char21{}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 \ensuremath{\gamma}. 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.