Disorder-induced spin-liquid-like behavior in kagome-lattice compounds

Quantum spin liquids (QSLs) are an exotic state of matter that is subject to extensive research. However, the relationship between the ubiquitous disorder and the QSL behaviors is still unclear. Here, by performing comparative experimental studies on two kagomé-lattice QSL candidates, Tm₃Sb₃Zn₂O₁₄ and Tm₃Sb₃Mg₂O₁₄ , which are isostructural to each other but with strong and weak structural disorder, respectively, we show unambiguously that the disorder can induce spin-liquid-like features. In particular, both compounds show dominant antiferromagnetic interactions with a Curie-Weiss temperature of -17.4 and -28.7 K for Tm₃Sb₃Zn₂O₁₄ and Tm₃Sb₃Mg₂O₁₄ , respectively, but remain disordered down to about 0.05 K. Specific-heat results suggest the presence of gapless magnetic excitations characterized by a residual linear term. Magnetic excitation spectra obtained by inelastic neutron scattering (INS) at low temperatures display broad continua. All these observations are consistent with those of a QSL. However, we find in Tm₃Sb₃Zn₂O₁₄ , which has strong disorder resulting from the random mixing of the magnetic Tm^{3 +} and nonmagnetic Zn^{2 +}, that the low-energy magnetic excitations observed in the specific-heat and INS measurements are substantially enhanced compared to those of Tm₃Sb₃Mg₂O₁₄ , which has much less disorder. We believe that the effective spins of the Tm^{3 +} ions in the Zn^{2 +}/Mg^{2 +} sites give rise to the low-energy magnetic excitations, and the amount of the occupancy determines the excitation strength. These results provide direct evidence of the mimicry of a QSL caused by disorder.