Possible gapless spin liquid in a rare-earth kagomé lattice magnet Tm${}_3$Sb${}_3$Zn${}_2$O${}_{14}$

Abstract

We report the thermodynamic and muon spin relaxation ($\mu$SR) evidences for a possible gapless spin liquid in Tm${}_3$Sb${}_3$Zn${}_2$O${}_{14}$, with the rare-earth ions Tm${}^{3+}$ forming a two-dimensional kagomé lattice. We extract the magnetic specific heat of Tm${}_3$Sb${}_3$Zn${}_2$O${}_{14}$ by subtracting the phonon contribution of the non-magnetic isostructural material La${}_3$Sb${}_3$Zn${}_2$O${}_{14}$. We obtain a clear linear-$T$ temperature dependence of magnetic specific heat at low temperatures, with the heat-capacity coefficient $\gamma$ = 26.6(1) mJ mol-Tm${}^{-1}$ K${}^{-2}$ in the zero temperature limit. No long-range magnetic order was observed down to 0.35 K in the heat capacity measurement. A broad hump around 9 K was observed in the zero field magnetic specific heat and is gradually suppressed in the magnetic fields that also create a spin gap in the specific heat. The absence of magnetic order is further confirmed by the $\mu$SR measurement down to 20 mK. We find that the spin-lattice relaxation time remains constant down to the lowest temperatures. We point out that the physics in Tm${}_3$Sb${}_3$Zn${}_2$O${}_{14}$ is fundamentally different from the Cu-based herbertsmithite and propose spin liquid ground states with non-Kramers doublets on the kagomé lattice to account for the experimental results.

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