Field-tunable quantum disordered ground state in the triangular-lattice antiferromagnet NaYbO2

Abstract

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

Field-induced magnetic transition and spin fluctuations in the quantum spin-liquid candidate CsYbSe2

“…The heat capacity goes to Dulong-Petit limit of phonon contribution around 100 J/mol K [57]. A broad peak is found below 10 K, which is similar to that observed in the other Yb-112 materials implying the QSL states in the triangular Heisenberg lattices [42,58,59]. There is no λ anomaly around 1.5 K, confirming short range correlations found in the magnetization.…”

“…Based on the magnetization and heat capacity results, in each other. Note that the dome feature for LRO is also found in other frustrated magnetic materials [41,42,60].…”

“…The 2D ratio d inter /d NN = 2 varies from 1.6 for NaYbO 2 to 2.47 for YbMgGaO 4 . This difference of the 2D ratio reflects on the different field-induced magnetic transition at low temperature in NaYbO 2 and YbMgGaO 4 [32,41,42]. Based on two-dimensional CsYbSe 2 structure, it inspires us to investigate the details of magnetic properties using the single crystals.…”

“…Magnetic fields perturb the quantum disordered ground state and induce the long-range order up-updown spin state in NaYbO 2 [40][41][42]. This field induced quantum phase transition, evoking alternative ground states, is an intriguing phenomenon in the frustrated triangular system.…”

Spin liquids in geometrically perfect triangular antiferromagnets

“…11). The absence of randomness was indeed confirmed in NaYbO 2 [138,145,146] by the observation of three resolution-limited peaks of the CEF excitations and the absence of extra features in high-energy inelastic neutron spectra [138]. No significant randomness is expected in the isostructural materials NaYbS 2 [147] and NaYbSe 2 [148] as well.…”