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1. Evidence for field induced quantum spin liquid behavior in a spin-1/2 honeycomb magnet

   https://doi.org/10.59717/j.xinn-mater.2024.100082  

   Lin, Gaoting; Shu, Mingfang; Zhao, Qirong; Li, Gang; Ma, Yinina; Jiao, Jinlong; Li, Yuting; Duan, Guijing; Huang, Qing; Sheng, Jieming; et al (January 2024, The Innovation Materials)

   One of the most important issues in modern condensed matter physics is the realization of fractionalized excitations, such as the Majorana excitations in the Kitaev quantum spin liquid. To this aim, the 3d-based Kitaev material Na₂Co₂TeO₆ is a promising candidate whose magnetic phase diagram of B // a* contains a field-induced intermediate magnetically disordered phase within 7.5 T < |B| < 10 T. The experimental observations, including the restoration of the crystalline point group symmetry in the angle-dependent torque and the coexisting magnon excitations and spinon-continuum in the inelastic neutron scattering spectrum, provide strong evidence that this disordered phase is a field induced quantum spin liquid with partially polarized spins. Our variational Monte Carlo simulation with the effective K-J₁-Γ-Γ'-J₃ model reproduces the experimental data and further supports this conclusion. 

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2. Pressure tuning of Kitaev spin liquid candidate Na3Co2SbO6

   https://doi.org/10.1038/s42005-025-02174-2  

   Poldi, E_H T; Tartaglia, R; Fabbris, G; Nguyen, N; Park, H; Liu, Z; van_Veenendaal, M; Kumar, R; Jose, G; Samanta, S; et al (December 2025, Communications Physics)

   Abstract The search for Kitaev’s quantum spin liquid in real materials has recently expanded with the prediction that honeycomb lattices of divalent, high-spin cobalt ions could host the dominant bond-dependent exchange interactions required to stabilize the elusive entangled quantum state. The layered honeycomb Na₃Co₂SbO₆has been singled out as a leading candidate provided that the trigonal crystal field acting on Co 3dorbitals, which enhances non-Kitaev exchange interactions between$${J}_{{{\rm{eff}}}}=\frac{1}{2}$$ $J_{\mathrm{eff}}=\frac{1}{2}$spin-orbital pseudospins, is reduced. Here we show that applied pressure leads to anisotropic compression of the layered structure, significantly reducing the trigonal distortion of CoO₆octahedra. Ferromagnetic correlations between pseudospins are enhanced in the spin-polarized (3 Tesla) phase up to about 60 GPa. Higher pressures drive a high-spin to low-spin transition destroying the$${J}_{{{\rm{eff}}}}=\frac{1}{2}$$ $J_{\mathrm{eff}}=\frac{1}{2}$moments required to map the spin Hamiltonian into Kitaev’s model. The spin transition strongly suppresses the low-temperature magnetic susceptibility and appears to stabilize a paramagnetic phase driven by frustration. The possible emergence of frustrated magnetism of localized$$S=\frac{1}{2}$$ $S=\frac{1}{2}$moments opens the door for exploration of novel magnetic quantum states in compressed honeycomb lattices of divalent cobaltates. 

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3. Momentum-independent magnetic excitation continuum in the honeycomb iridate H3LiIr2O6

   https://doi.org/10.1038/s41467-023-40769-x  

   de_la_Torre, A; Zager, B; Bahrami, F; Upton, M H; Kim, J; Fabbris, G; Lee, G-H; Yang, W; Haskel, D; Tafti, F; et al (December 2023, Nature Communications)

   Abstract Understanding the interplay between the inherent disorder and the correlated fluctuating-spin ground state is a key element in the search for quantum spin liquids. H₃LiIr₂O₆is considered to be a spin liquid that is proximate to the Kitaev-limit quantum spin liquid. Its ground state shows no magnetic order or spin freezing as expected for the spin liquid state. However, hydrogen zero-point motion and stacking faults are known to be present. The resulting bond disorder has been invoked to explain the existence of unexpected low-energy spin excitations, although data interpretation remains challenging. Here, we use resonant X-ray spectroscopies to map the collective excitations in H₃LiIr₂O₆and characterize its magnetic state. In the low-temperature correlated state, we reveal a broad bandwidth of magnetic excitations. The central energy and the high-energy tail of the continuum are consistent with expectations for dominant ferromagnetic Kitaev interactions between dynamically fluctuating spins. Furthermore, the absence of a momentum dependence to these excitations are consistent with disorder-induced broken translational invariance. Our low-energy data and the energy and width of the crystal field excitations support an interpretation of H₃LiIr₂O₆as a disordered topological spin liquid in close proximity to bond-disordered versions of the Kitaev quantum spin liquid. 

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4. Magnetic field effects on the quantum spin liquid behaviors of NaYbS2

   https://doi.org/10.1007/s44214-022-00011-z  

   Wu, Jiangtao; Li, Jianshu; Zhang, Zheng; Liu, Changle; Gao, Yong Hao; Feng, Erxi; Deng, Guochu; Ren, Qingyong; Wang, Zhe; Chen, Rui; et al (December 2022, Quantum Frontiers)

   Abstract Spin-orbit coupling is an important ingredient to regulate the many-body physics, especially for many spin liquid candidate materials such as rare-earth magnets and Kitaev materials. The rare-earth chalcogenides Equation missing<#comment/>(Ch = O, S, Se) is a congenital frustrating system to exhibit the intrinsic landmark of spin liquid by eliminating both the site disorders between Equation missing<#comment/>and Equation missing<#comment/>ions with the big ionic size difference and the Dzyaloshinskii-Moriya interaction with the perfect triangular lattice of the Equation missing<#comment/>ions. The temperature versus magnetic-field phase diagram is established by the magnetization, specific heat, and neutron-scattering measurements. Notably, the neutron diffraction spectra and the magnetization curve might provide microscopic evidence for a series of spin configuration for in-plane fields, which include the disordered spin liquid state, 120° antiferromagnet, and one-half magnetization state. Furthermore, the ground state is suggested to be a gapless spin liquid from inelastic neutron scattering, and the magnetic field adjusts the spin orbit coupling. Therefore, the strong spin-orbit coupling in the frustrated quantum magnet substantially enriches low-energy spin physics. This rare-earth family could offer a good platform for exploring the quantum spin liquid ground state and quantum magnetic transitions. 

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5. Vacancy-Induced Low-Energy Density of States in the Kitaev Spin Liquid

   https://doi.org/doi.org/10.1103/PhysRevX.11.011034  

   Wen-Han Kao, Johannes Knolle (February 2021, PRX action)

   null (Ed.)

   The Kitaev honeycomb model has attracted significant attention due to its exactly solvable spin-liquid ground state with fractionalized Majorana excitations and its possible materialization in magnetic Mott insulators with strong spin-orbit couplings. Recently, the 5d-electron compound H3LiIr2O6 has shown to be a strong candidate for Kitaev physics considering the absence of any signs of a long-range ordered magnetic state. In this work, we demonstrate that a finite density of random vacancies in the Kitaev model gives rise to a striking pileup of low-energy Majorana eigenmodes and reproduces the apparent power-law upturn in the specific heat measurements of H3LiIr2O6. Physically, the vacancies can originate from various sources such as missing magnetic moments or the presence of nonmagnetic impurities (true vacancies), or from local weak couplings of magnetic moments due to strong but rare bond randomness (quasivacancies). We show numerically that the vacancy effect is readily detectable even at low vacancy concentrations and that it is not very sensitive either to the nature of vacancies or to different flux backgrounds. We also study the response of the site-diluted Kitaev spin liquid to the three-spin interaction term, which breaks time-reversal symmetry and imitates an external magnetic field. We propose a field-induced flux-sector transition where the ground state becomes flux-free for larger fields, resulting in a clear suppression of the low-temperature specific heat. Finally, we discuss the effect of dangling Majorana fermions in the case of true vacancies and show that their coupling to an applied magnetic field via the Zeeman interaction can also account for the scaling behavior in the high-field limit observed in H3LiIr2O6. 

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