We report the synthesis and properties of ${\left(\mathrm{H},\mathrm{Li}\right)}_6{\mathrm{Ru}}_2{\mathrm{O}}_6$, which is shown to be a $J_{\mathrm{eff}}=\frac{1}{2}$ system made out of ${\mathrm{Ru}}^{3+}$ moments in a honeycomb geometry. Bulk magnetization, heat capacity, nuclear magnetic resonance (NMR), and muon spin relaxation rule out the presence of static moments or any spin glass phase down to 84 mK. All techniques suggest a crossover to a liquidlike state below about 40 K. The ${}^7\mathrm{Li}$ NMR shift data suggest a nonzero $T$-independent spin susceptibility at low $T$. In zero field, $C_m/T$ shows $T^{-0.9}$ divergence which is consistent with vacancy-induced effects on low-energy excitations of the pristine Kitaev spin liquid. With field, power-law variations in the ${}^7\mathrm{Li}$ NMR spin-lattice relaxation rate $1/T_1$ and magnetic heat capacity $C_m$ show quantitatively different scaling behaviors as compared to those in ${\mathrm{H}}_3{\mathrm{LiIr}}_2{\mathrm{O}}_6$. A two-step entropy release in heat capacity is also observed putatively from $Z_2$ flux (low-$T$ step) and itinerant Majorana fermions (high-$T$ step). Based on these findings, we propose that ${\left(\mathrm{H},\mathrm{Li}\right)}_6{\mathrm{Ru}}_2{\mathrm{O}}_6$ realizes a Kitaev spin liquid with no evidence of inherent magnetic ordering in zero field unlike $\alpha \text{−}{\mathrm{RuCl}}_3$ where an 8-T field is required to suppress magnetic order.

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• Quantum spin liquid
• Honeycomb lattice
• Muon spin relaxation & rotation
• Nuclear magnetic resonance
• Specific heat measurements
• Susceptibility measurements