Spin-liquid-like spin dynamics in the frustrated antiferromagnet TbBO3

The synergistic interplay between spin correlations, spin-orbit coupling, and competing exchange interactions provides a promising route to realize exotic quantum states with nontrivial excitations in rare-earth based frustrated magnets. Here, by using thermodynamic and local-probe measurements down to 16 mK, we demonstrate the exotic magnetism and spin dynamics in the distorted triangular lattice TbBO3. Thermodynamic experiments reveal the presence of dominant antiferromagnetic exchange and subdominant dipolar interactions. Despite sizable antiferromagnetic exchange interactions between the Tb3+ moments, muon-spin relaxation experiment does not detect any signatures of long-range magnetic order or spin-freezing down to 16 mK, corroborating the specific heat and ac magnetic susceptibility down to 45 mK that suggests a persistent spin dynamics in this frustrated triangular lattice. The scaling of muon relaxation rate as a function of the characteristic energy scale for several spin-liquid candidates, including TbBO3, demonstrates that a common underlying mechanism is at play. The persistent dynamics in this frustrated triangular lattice antiferromagnet is reminiscent of a universal spin-liquid-like spin fluctuations, here attributed to dominant two dimensional (2D) antiferromagnetic short-range spin correlations, confirmed by the presence of a broad magnetic diffuse scattering in the elastic and low-energy inelastic neutron scattering channels at Q ~ 1.03 Ang**$^{-1}$** at low temperatures. Our results demonstrate that non-Kramers ion based triangular lattice hosts spin-liquid-like dynamics of local moments arising from the admixture of excited crystal electric field states into the ground state and intertwining of frustration and spin-orbit interaction.