Bulletin of the American Physical Society
APS March Meeting 2022
Volume 67, Number 3
Monday–Friday, March 14–18, 2022; Chicago
Session B51: Kitaev Materials IFocus Recordings Available

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Sponsoring Units: GMAG DCMP Chair: Wen Han Kao, University of Minnesota Room: McCormick Place W474B 
Monday, March 14, 2022 11:30AM  12:06PM 
B51.00001: Kitaev Spin Liquid in 3d Transition Metal Compounds Invited Speaker: Huimei Liu We have proposed that 3d honeycomb cobaltates are very promising candidates to realize the Kitaev spin liquid state, thanks to the easy tunability of the exchange Hamiltonian in favor of Kitaev interaction [13]. The key parameters that have major impacts on the exchange constants, such as the chargetransfer gap and the trigonal crystal field, are discussed. Several materials are considered as examples to show the proximity to the Kitaev spin liquid phase, and can be driven into it by lattice engineering. Our theoretical predications suggest that cobaltates offer the most promising search area for Kitaev model physics. 
Monday, March 14, 2022 12:06PM  12:18PM 
B51.00002: Thermal Transport of Cobased Kitaev Material BaCo2(AsO4)2 Jiayi Hu, Peter A Czajka, Phuan Ong, Ruidan Zhong, Robert J Cava The Kitaev Quantum Spin Liquid (KQSL) has attracted much attention because the Kitaev Hamiltonian can be solved exactly and its excitations are Majorana fermions and vortices. Previous work has mostly focused on 4d and 5d transition metal based materials, such as aRuCl3. Here we present measurements on a Cobased honeycomb material BaCo2(AsO4)2, which exhibits different interaction energy scales that may lead to a more ideal Kitaev material. For example, it has a lower critical field for suppressing antiferromagnetism than that in RuCl3. This enables easier access to the candidate fieldinduced spin liquid state. We have explored its rich temperaturefield phase diagram via thermal transport measurements. Our results reveal remarkable sensitivity of the thermal conductivity to the underlying magnetic phases and transitions between them. In particular, we present magnetic hysteresis and thermal hall data that provide new information about the underlying states and Kitaev physics more broadly. 
Monday, March 14, 2022 12:18PM  12:30PM 
B51.00003: Magnetic interactions in the quantum spin liquid candidate Na_{2}BaCo(PO_{4})_{2} Jared Gdanski, Guangyong Xu, Ruidan Zhong, Robert J Cava, Franz Demmel, Suheon Lee, YuanMing Lu, Zhijun Xu Motivated by the recent discovery of the quantum spin liquid (QSL) candidate material Na_{2}BaCo(PO_{4})_{2} (PNAS 116 (29) 1450514510), we use inelastic neutron scattering to determine the magnetic interaction in this material. We find that an outofplane magnetic field of larger than 3 T is enough to destroy the QSL phase and polarize the spins in the system, where a welldefined spin wave dispersion emerges. By fitting the observed spin wave spectrum with a linear spin wave theory, we are able to obtain the magnetic interactions in the system. We find that the nearest neighbor exchange interaction is dominated by an easyaxis Ising interaction and a bonddependent Kitaevtype exchange interaction. Our study paves the way to understand the nature of the plausible QSL phase in Na_{2}BaCo(PO_{4})_{2}. 
Monday, March 14, 2022 12:30PM  12:42PM 
B51.00004: Frustrated magnetism in IsingKitaevGamma model on the triangular lattice Yonas Getachew, Rebecca Chan, Wayne Zheng Motivated by the discovery of quantum spin liquid candidate Na_{2}BaCo(PO_{4})_{2} and recent fielddependent inelastic neutron scattering study on this material, we theoretically investigate the phase diagram of a frustrated spin1/2 model on the triangular lattice. Competing antiferromagnetic Ising, bonddependent exchange (Kitaev) and anisotropic symmetric exchange (Gamma) interactions give rise to a rich phase diagram. Remarkably, aside from various magnetic orders, a gapless quantum spin liquid phase emerges. We present a comprehensive study of the phase diagram, by combining semiclassical method and numerical methods including exact diagonalization and density matrix renormalization group. 
Monday, March 14, 2022 12:42PM  12:54PM Withdrawn 
B51.00005: Ba_{3}Co_{2}O_{6}(CO_{3})_{0.7}: Candidate SpinLiquid on the HoneycombLattice Andrew S Padgett Since P.W. Anderson proposed the theoretical existence of the quantum spin liquid ground state in 1973, antiferromagnetic spin1/2 systems exhibiting large quantum fluctuations have attracted significant interest as spin liquid candidates. The experimental verification of the spin liquid ground state would not only advance fundamental condensed matter physics, but also provide a path forward to discovering new, exotic spin system ground states. If only nearest neighbor interactions are considered, the spin1/2 Heisenberg antiferromagnet on a honeycomb lattice should order in a Néel ground state. However, sufficiently strong next nearest neighbor interactions combined with a small coordination number and low dimensionality, which increase the role of quantum fluctuations, such as those exhibited in Ba_{3}Co_{2}O_{6}(CO_{3})_{0.7}, could result in a quantum spin liquid ground state. For this reason, we have investigated the low temperature specific heat and magnetization of Ba_{3}Co_{2}O_{6}(CO_{3})_{0.7}, a nonstoichiometric compound with the CoO_{6} chains forming a honeycomb lattice. The magnetization exhibits an anomalous decrease in slope with increasing field beyond 10 T when the field is applied parallel to the c axis of the sample, indicating that randomness plays an important role in Ba_{3}Co_{2}O_{6}(CO_{3})_{0.7}. Specific heat measurements failed to show any sign of ordering down to 160 mK in fields between zero and 18 T. This corroborates earlier measurements made at higher temperatures over a narrower field range by Igarashi et al. Further, the specific heat behaves linearly at temperatures below 700 mK. Interestingly, Ba_{3}Co_{2}O_{6}(CO_{3})_{0.7} has a very large Wilson ratio. Although not a theoretical prediction of any quantum spin liquid models, all known spin liquid candidates exhibit Wilson ratios greater than 1, often times greater by an order of magnitude. Herein we discuss our motivation, experiments, and results which advance strong evidence that Ba_{3}Co_{2}O_{6}(CO_{3})_{0.7} hosts a spin liquid ground state. 
Monday, March 14, 2022 12:54PM  1:06PM 
B51.00006: New experimental strategies to explore the Kitaev interaction in honeycomb Mott insulators JIEFU CEN, HaeYoung Kee Twodimensional van der Waals honeycomb ferromagnets such as CrI_{3} have attracted a lot of interest because of their potential applications in spintronics. We propose new experimental strategies to explore the bonddependent interactions in honeycomb ferromagnets based on symmetries. These new methods can help resolve the debate on the importance of Kitaev interaction in CrI_{3} from recent angledependent ferromagnetic resonance experiments and inelastic neutron scattering spin gap measurements. These strategies in general can be applied to other systems with similar symmetries. 
Monday, March 14, 2022 1:06PM  1:18PM 
B51.00007: Pressure tuning of magnetism in pseudospin1/2 honeycomb oxide Na_{2}Co_{2}TeO_{6} Tongxie Zhang, Liangzi Deng, Qing Huang, Sammy Bourji, Gaihua Ye, Kevin Gutierrez, Rui He, Haidong Zhou, ChingWu Chu, Shixiong Zhang Honeycomb magnets have attracted significant interest because of their potential for realizing exotic magnetic states including the Kitaev quantum spin liquid phase. Among various Kitaev candidates, Na_{2}Co_{2}TeO_{6 }is a d^{7} highspin compound in which the pseudospin1/2 Co^{2+} ions form a longrange antiferromagnetic order below ~27 K. As pressure is an effective parameter to tune interactions in many systems, here we study the possibility of tuning the ordered state of Na_{2}Co_{2}TeO_{6 }into a spin disordered or liquid state under the application of hydrostatic pressure up to 13 kbar. Temperature dependence of magnetization at ambient pressure shows a magnetic phase transition at T_{N} ~27 K, which is followed by a minor kink at T_{F}~16 K. While pressure has a negligible influence on the magnetic ordering temperature, it reduces the outofplane magnetization between 16 K and 27 K. We will further discuss how the pressure influences the inplane magnetization as well as the critical magnetic field at which a spindisordered like state is induced. 
Monday, March 14, 2022 1:18PM  1:54PM 
B51.00008: Magnetic Field Induced Disorder State in 3d Honeycomb Oxide Na_{2}Co_{2}TeO_{6} Invited Speaker: Jie Ma Investigating the exotic quantum phenomena and the related ground state of the frustrated quantum magnets is a focus of condensed matter physics over the past years. While the realization of quantum spin liquid (QSL) without conventional magnetic ordering even down to 0 K is a challenging task, the Kitaev model is a prominent example with an exactly solvable spin model. The Kitaev materials so far have been focused on 4d/5d based systems with effective spin1/2, such as H_{3}LiIr_{2}O_{6}, αLi_{2}IrO_{3}, αNa_{2}IrO_{3,} and αRuCl_{3}, which exhibit zigzag antiferromagnetic (AFM) ordering at zero magnetic field owing to nonKitaev interactions. Recently, the theoretical studies propose that the 3dcobalt honeycomb magnets with effective spin1/2 can be another playground to realize the Kitaev model. The nonKitaev terms have been predicted to be almost vanishing with the small trigonal crystal fields acting on Co^{2+} ions, which makes the cobaltates as one good system for Kitaev physics. We studied the potential candidate Na_{2}Co_{2}TeO_{6} and performed magnetization, heat capacity, highfield electric spin resonance, and inelastic neutron scattering (INS) measurements. A complicated magnetic fieldtemperature phase diagram was demonstrated with a zigzag AFM state and spin gap was observed in the spin dynamics. A quantum spin disordered state is induced by an abplane magnetic field between 7.5 and 10.5 T like the fieldinduced QSL in αRuCl_{3}. Through detailed theoretical simulations on the INS spinwave spectrum, we could obtain different ratios of the Kitaev interaction and the Heisenberg exchange. Hence, we anticipate our work will generate significant interest: it will trigger new experimental efforts for other realizations of magnetic field inducing the exotic quantum states and rejuvenate theoretical and computational efforts to understand the elusive dynamics in the Kitaev model for frustrated quantum magnetism. 
Monday, March 14, 2022 1:54PM  2:06PM 
B51.00009: Infrared and Raman spectroscopy study of Cobased honeycomb Na_{2}Co_{2}TeO_{6} Li Xiang, Yuxuan Jiang, Mykhaylo Ozerov, Qing Huang, Haidong Zhou, Zhigang Jiang, Dmitry Smirnov Layered honeycomb magnets have received lots of attention as potential candidates to realize Kitaev physics. Current studies focus on 4d or 5dtransitionmetal honeycomb compounds for strong spinorbit coupling. Recently, theoretical calculations propose that Kitaev interactions can also be realized in honeycomb magnets from 3dtransitionmetal compounds [1,2]. Among them, Cobased honeycomb Na_{2}Co_{2}TeO_{6} (NCTO) is antiferromagnetic ordered below T_{N} = 25K. More recent experimental studies on NCTO suggest that below T_{N}, magnetic field can suppress the longrange AFM order, and induce a disordered state in the field range of 7.5T < B < 10.5T before a field polarized state. Here we report the lowfrequency infrared and Raman spectroscopy study on NCTO at low temperature and under high magnetic field up to 14T. A rich structure of magnetic excitations is observed across the AFM, disordered and polarized stats. The measurement results will be further discussed with theoretical calculations. 
Monday, March 14, 2022 2:06PM  2:18PM 
B51.00010: Antiferromagnetic Kitaev interaction in J_{eff}=1/2 cobalt honeycomb materials Na_{3}Co_{2}SbO_{6} and Na_{2}Co_{2}TeO_{6} Chaebin Kim, Jaehong Jeong, Gaoting Lin, Pyeongjae Park, Takatsugu Masuda, Shinichiro Asai, Shinichi Itoh, HeungSik Kim, Haidong Zhou, Jie Ma, JeGeun Park Finding new materials with antiferromagnetic (AFM) Kitaev interaction is an urgent issue for quantum magnetism research [1]. In this work, we conclude that Na_{3}Co_{2}SbO_{6} and Na_{2}Co_{2}TeO_{6} are new honeycomb cobaltbased systems with AFM Kitaev interaction by carrying out inelastic neutron scattering experiments and subsequent analysis [1]. The spinorbit excitons observed at 2028 meV in both compounds strongly support the idea that Co^{2+} ions of both compounds have a spinorbital entangled J_{eff}=1/2 state. Furthermore, we found that a generalized KitaevHeisenberg Hamiltonian can describe the spinwave excitations of both compounds with additional 3^{rd} nearestneighbor interaction. Our bestfit parameters show significant AFM Kitaev terms and offdiagonal symmetric anisotropy terms of a similar magnitude in both compounds. We also found a strong magnondamping effect at the higher energy part of the spin waves, entirely consistent with observations in other Kitaev magnets. Our work suggests Na_{3}Co_{2}SbO_{6} and Na_{2}Co_{2}TeO_{6} as rare examples of the AFM Kitaev magnets based on the systematic studies of the spin waves and analysis. 
Monday, March 14, 2022 2:18PM  2:30PM 
B51.00011: Identification of a Kitaev Quantum Spin Liquid by Magnetic Field Angle Dependence Kyusung Hwang, Ara Go, Ji Heon Seong, Takasada Shibauchi, EunGook Moon Quantum spin liquids realize massive entanglement and fractional quasiparticles from localized spins, proposed as an avenue for quantum science and technology. In particular, topological quantum computations are suggested in the nonabelian phase of Kitaev quantum spin liquid with Majorana fermions, and detection of Majorana fermions is one of the most outstanding problems in modern condensed matter physics. Here, we propose a concrete way to identify the nonabelian Kitaev quantum spin liquid by magnetic field angle dependence. Topologically protected critical lines exist on a plane of magnetic field angles, and their shapes are determined by microscopic spin interactions. A chirality operator plays a key role in demonstrating microscopic dependences of the critical lines. We also show that the chirality operator can be used to evaluate topological properties of the nonabelian Kitaev quantum spin liquid without relying on Majorana fermion descriptions. Experimental criteria for the nonabelian spin liquid state are provided for future experiments. 
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