Antiferromagnetically coupled S=1/2 spins on an isotropic triangular lattice is the paradigm of frustrated quantum magnetism, but structurally ideal realizations are rare. Here we investigate NaYbO2, which hosts an ideal triangular lattice of Jeff=1/2 moments with no inherent site disorder. No signatures of conventional magnetic order appear down to 50 mK, strongly suggesting a quantum spin liquid ground state. We observe a two-peak specific heat and a nearly quadratic temperature dependence in accord with expectations for a two-dimensional Dirac spin liquid. Application of a magnetic field strongly perturbs the quantum disordered ground state and induces a clear transition into a collinear ordered state consistent with a long-predicted "up-up-down" structure for a triangular lattice XXZ Hamiltonian driven by quantum fluctuations. The observation of spin liquid signatures in zero field and quantum-induced ordering in intermediate fields in the same compound demonstrate an intrinsically quantum disordered ground state. We conclude that NaYbO2 is a model, versatile platform for exploring spin liquid physics with full tunability of field and temperature.Exotic ground states of quantum antiferromagnets are encouraged by the combination of low dimensionality, geometric frustration, and inherent anisotropies. Planar triangular lattices have long been sought as platforms for stabilizing them 1-7 ; however, ideal manifestations that do not break crystallographic or exchange symmetries upon approaching the quantum regime are rare. The organic compounds κ-(BEDT-TTF)2Cu2(CN)3 8 and EtMe3Sb[Pd(dmit)2]2 9 are two promising examples of triangular lattices with S=1/2 moments and a dynamically disordered spin ground state. However, S=1/2 inorganic analogs such as Ba3CoSb2O9 10 , Ba8CoNb6O24 11 , and NaTiO2 12-14 either order magnetically or undergo a lattice deformation and dimerization upon cooling. A key roadblock in inorganic systems is the identification of a material with a high crystallographic symmetry, rigid structure, and minimal defect mechanisms that also contains magnetic ions possessing strong quantum fluctuations. Ideally, the magnetic ions should be located at high symmetry positions that preclude antisymmetric Dzyaloshinskii-Moriya exchange from lifting geometric frustration at low temperatures.As an alternative to S=1/2 based compounds, rare earth ions with ground state doublets may also engender enhanced quantum fluctuations when decorating a triangular lattice. Specifically, recent studies have shown that the spin-orbit entangled Jeff=1/2 moments of Yb 3+ ions on this lattice may exhibit a variety of nearly degenerate magnetic states 15-22 . Given the appropriate anisotropies and when driven close

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We have carried out muon spin relaxation and rotation measurements on the newly discovered kagome metal KV3Sb5, and find a local field dominated by weak magnetic disorder which we associate with the nuclear moments present, and a modest temperature dependence which tracks the bulk magnetic susceptibility. We find no evidence for the existence of V4+ local moments, suggesting that the physics underlying the recently reported giant unconventional anomalous Hall effect in this material warrants further studies.

Anyonic excitations emerging from a Kitaev spin liquid can form a basis for quantum computers 1, 2 . Searching for such excitations motivated intense research on the honeycomb iridate materials 3-17 . However, access to a spin liquid ground state has been hindered by magnetic ordering 5 . Cu 2 IrO 3 is a new honeycomb iridate without thermodynamic signatures of a long-range order 18 . Here, we use muon spin relaxation to uncover the magnetic ground state of Cu 2 IrO 3 . We find a two-component depolarization with slow and fast relaxation rates corresponding to distinct regions with dynamic and static magnetism, respectively. X-ray absorption spectroscopy and first principles calculations identify a mixed copper valence as the origin of this behavior. Our results suggest that a minority of Cu 2+ ions nucleate regions of static magnetism whereas the majority of Cu + /Ir 4+ on the honeycomb lattice give rise to a Kitaev spin liquid.

The search for an ideal Kitaev spin liquid candidate with anyonic excitations and long-range entanglement has motivated the synthesis of a new family of intercalated Kitaev magnets such as H 3 LiIr 2 O 6 , Cu 2 IrO 3 , and Ag 3 LiIr 2 O 6 . The absence of a susceptibility peak and a two-step release of the magnetic entropy in these materials have been proposed as evidence of proximity to the Kitaev spin liquid. Here we present a comparative study of the magnetic susceptibility, heat capacity, and muon spin relaxation (μSR) between two samples of Ag 3 LiIr 2 O 6 in the clean and disordered limits. In the disordered limit, the absence of a peak in either susceptibility or heat capacity and the lack of zero-field muon precession in the μSR signal give the impression of a proximate spin liquid state. However, in the clean limit, peaks are resolved in both susceptibility and heat capacity, and spontaneous oscillations appear in the μSR signal, confirming long-range antiferromagnetic order in the ground state. The μSR oscillations fit to a Bessel function, characteristic of incommensurate order, as reported in the parent compound α-Li 2 IrO 3 . Our results clarify the role of structural disorder in the intercalated Kitaev magnets.