Field-tunable quantum disordered ground state in the triangular lattice antiferromagnet NaYbO$_2$ (1901.09408v2)

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 NaYbO$2$, which hosts an ideal triangular lattice of $J{eff}=1/2$ 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 NaYbO$_2$ is a model, versatile platform for exploring spin liquid physics with full tunability of field and temperature.

Field-Induced Quantum Disordered State in NaYbO2

The paper provides an extensive experimental and theoretical investigation into the frustrated quantum magnetic system NaYbO₂, which features an isotropic triangular lattice of antiferromagnetically coupled $J_{\text{eff}}=1/2$ spins. This paper stands out as it explores both the intrinsic quantum disordered ground state of this compound and the magnetic field-induced transition to an ordered state, elucidating the delicate balance of quantum fluctuations and geometric frustration inherent to such systems.

Key Observations

The research presented herein primarily leverages neutron scattering, magnetization, susceptibility, and heat capacity measurements to characterize the spin dynamics in NaYbO₂. Key findings include:

• Quantum Spin Liquid State: Down to 50 mK, NaYbO₂ exhibits no signatures of conventional magnetic ordering, providing evidence for a quantum spin liquid ground state.
• Specific Heat Behavior: Observations reveal a two-peak specific heat and a quadratic temperature dependence, supporting theoretical predictions for a two-dimensional Dirac spin liquid. The dual peak structure suggests short-range correlations followed by quantum spin singlet state formation.
• Field-Induced Transition: Application of a magnetic field leads to a transition to a collinear "up-up-down" ordered state, aligning with the well-established XXZ model prediction for such systems.

Experimental Insights

The paper utilizes neutron diffraction and inelastic neutron scattering to elaborate on spin ordering and excitations. Under a 5T magnetic field, the emergence of superlattice reflections rationalizes the transition to a collinear ordered state, further evidenced by linear spin wave calculations. Isothermal $\chi'(H)$ measurements delineate a critical phase boundary at approximately 3T, suggesting the emergence of a quantized magnetization plateau.

Theoretical Implications

The paper corroborates theoretical models predicting that NaYbO₂ is a platform for realizing a U(1) Dirac spin liquid state, characterized by gapless fermionic spinons and governed by a two-dimensional conformal field theory. The inter-play between in-plane and interlayer couplings is crucial; it is inferred that the interlayer exchange might be non-negligible, leading to quantum suppression of classical order due to frustrated interactions.

Future Prospects in AI and Quantum Magnetism

The findings from this paper contribute significantly to the understanding of quantum disordered systems on triangular lattices, paving the way for novel explorations in the field of quantum magnetism and condensed matter physics. Looking forward, such studies could enhance AI-driven modeling of quantum states or aid in the development of applications harnessing quantum spin liquid properties.

In conclusion, NaYbO₂ serves as an exceptional model for studying spin liquid states with modifiable magnetic properties, thereby providing a valuable framework for future investigations into novel quantum phases and their applications in theoretical and experimental physics.