Bulletin of the American Physical Society
APS March Meeting 2021
Monday–Friday, March 15–19, 2021; Virtual; Time Zone: Central Daylight Time, USA
Session A39: Kitaev Systems IFocus Live

Hide Abstracts 
Sponsoring Units: GMAG DMP Chair: Philipp Gegenwart, Augsburg University 
Monday, March 15, 2021 8:00AM  8:36AM Live 
A39.00001: Bond dependent spinorbital exchange and quantum orderbydisorder in CoTiO3 Invited Speaker: Paul McClarty There has been a great deal of interest in bonddependent anisotropic couplings in strong spinorbit coupled magnets  especially on iridates and ruthenates  that has brought new physics into focus. Recent theoretical work has proposed that such couplings can be significant in certain cobalt magnets where the spinorbit coupling is subdominant [1]. Here we report on CoTiO3, an insulating ABC stacked honeycomb easy plane magnet that orders into a structure with ferromagnetic layers stacked antiferromagnetically with a spin wave spectrum that is known to host Dirac magnons [2]. Our high resolution inelastic neutron scattering data clearly shows the presence of a magnon gap of about 1meV that must arise through the presence of bonddependent exchange couplings [3]. The spectral gap also provides strong evidence for the existence of a quantum orderbydisorder mechanism − a very rare phenomenon that selects the longranged ordered magnetic structure through the effect of quantum fluctuations  that, in this material, crucially involves virtual crystal field excitations. The same couplings that lead to the spectral gap also cause the Dirac magnons to wind around one another in a double helix structure and we show that the experimental data is consistent with this scenario. We also show the presence of dispersive exciton modes with Dirac nodes. All the key features of the experiment are explicable through a multiboson theory with spinorbital exchange couplings. 
Monday, March 15, 2021 8:36AM  8:48AM Live 
A39.00002: Easyplane anisotropicexchange honeycomb magnets: quantum effects and dealing with them Pavel Maksimov, Alexander Chernyshev We attempt a study of magnetic spectrum of the easyplane anisotropic spin model on a honeycomb lattice with bonddependent exchange interactions, which can be related to the extended KitaevHeisenberg model through the axes transformation. We find signatures of strong magnonmagnon interactions in both zerofield zigzag state, and the paramagnetic polarized phase. First, we show that the zigzag state is unstable towards magnon decays due to anisotropic terms. Next, we calculate selfenergy in the first order of 1/S approximation in the polarized phase, find strong renormalization of the real part of the spectrum near the critical point, and propose a novel way to regularize unphysical divergences. Finally, we obtain dynamical spin structure factor at the Γ point in the polarized phase, compare it to ESR and Raman experiments and show that the spectrum has features similar to those observed experimentally, such as (i) downward renormalization of the magnon mode due to repulsion from the twomagnon continuum, down to gap closure, and (ii) redistribution of the spectral weight from single magnon mode to the continuum. 
Monday, March 15, 2021 8:48AM  9:00AM Live 
A39.00003: HeisenbergKitaev models on hyperhoneycomb and stripyhoneycomb lattices: 3D–2D equivalence of ordered states and phase diagrams Wilhelm Krüger, Matthias Vojta, Lukas Janssen We discuss magnetically ordered states, arising in HeisenbergKitaev and related spin models, on threedimensional (3D) harmonic honeycomb lattices. For large classes of ordered states, we show that they can be mapped onto twodimensional (2D) counterparts on the honeycomb lattice, with the classical energetics being identical in the 2D and 3D cases. To make contact with the physics of the iridates Li_{2}IrO_{3}, we analyze a minimal model including a symmetric offdiagonal Γ interaction, discuss its 3D–2D mapping, and determine the relevant phases which are realized in the materials. In particular, we demonstrate explicitly the adiabatic equivalence of the spiral magnetic orders in α and βLi_{2}IrO_{3}. Our results pave the way to a systematic common understanding of 2D and 3D Kitaev materials. 
Monday, March 15, 2021 9:00AM  9:12AM Live 
A39.00004: SDRG Study of Random Kitaev Chains and Ladders WenHan Kao, Natalia Perkins Recent years have seen a vigorous experimental research campaign on identifying candidate materials for quantum spin liquids (QSL)  topological states of matter with longrange entanglement and the absence of any broken symmetries. Since some level of disorder in various forms is inevitable in real materials, the effect of quenched disorder in QSLs has arisen a lot of attention. Of specific interest is the role of disorder in the potential Kitaev QSL materials. Here we present a study of random spin1/2 chain and ladder with bonddirectional Kitaevlike interactions. The Kitaev chain consists of alternating 'xx' and 'yy' Ising interactions. By applying the strongdisorder renormalization group (SDRG) on the random Kitaev chain, we demonstrate the presence of infinitedisorder fixed point and quantum Griffiths phase in the lowenergy limit. In the Kitaev ladder, chains with alternating 'xx' and 'yy' bonds are connected by the 'zz' Ising interactions on the rungs. We show that the critical properties of the random Kitaev ladder are controlled by the flux operators which are included in the decimation procedure. As a result, local flux gaps get renormalized during SDRG and the lowenergy phase contains finite density of fluxes entangled with renormalized spin clusters. 
Monday, March 15, 2021 9:12AM  9:24AM Live 
A39.00005: Polarized Inelastic Neutron Scattering Results on the Kitaev SpinLiquid Candidate D_{3}LiIr_{2}O_{6} Thomas Halloran, Yishu Wang, Collin Leslie Broholm A central theme of condensed matter physics in recent years has been the realization of materials that exhibit a quantum spinliquid state beyond one dimension. The only model of the quantum spinliquid state that is exactly solvable is known as the Kitaev model, which consists of a 2D honeycomb lattice of J_{eff }= ½ moment magnetic ions. NMR and other bulk sample characterization has suggested that the properties of the material H_{3}LiIr_{2}O_{6} are consistent with those of a Kitaev spinliquid [1]. The structure consists of a honeycomb lattice of Ir^{4+} ions with strong spinorbit coupling to support the bond dependent exchange interactions required in the Kitaev model. Using inelastic neutron scattering on the SEQUOIA and HYSPEC instruments at ORNL, we probed the material for magnetic excitations. Both polarized and unpolarized inelastic studies reveal information regarding the low energy excitations in the potential KSL state. 
Monday, March 15, 2021 9:24AM  9:36AM 
A39.00006: Majoranamediated spin transport in Kitaev quantum spin liquids Tetsuya Minakawa, Yuta Murakami, Koga Akihisa, Joji Nasu We study the spin transport through the quantum spin liquid (QSL) by investigating the realtime and realspace dynamics of the Kitaev spin system with zigzag edges using the timedependent Majorana meanfield theory. After the magneticfield pulse is introduced to one of the edges, spin moments are excited in the opposite edge region although spin moments are never induced in the Kitaev QSL region. This unusual spin transport originates from the fact that the S=1/2 spins are fractionalized into the itinerant and localized Majorana fermions in the Kitaev system. Although both Majorana fermions are excited by the magnetic pulse, only the itinerant ones flow through the bulk regime without spin excitations, resulting in the spin transport in the Kitaev system despite the presence of a nonzero spin gap. We also demonstrate that this phenomenon can be observed in the system with small Heisenberg interactions using the exact diagonalization. 
Monday, March 15, 2021 9:36AM  9:48AM Live 
A39.00007: Low Temperature Thermal Transport in RuCl3 Peter Czajka, Tong Gao, Max Hirschberger, Paula Lampenkelley, Arnab Banerjee, Jiaqiang Yan, David George Mandrus, Stephen E Nagler, N. Phuan Ong RuCl3 is currently the primary material candidate for realizing the Kitaev Honeycomb model and its exotic Majorana fermion excitations. We have measured the longitudinal and Hall thermal conductivity of RuCl3 down to He3 temperatures (0.3 K). The longitudinal thermal conductivity displays periodic oscillations that may be indicative of Landau quantization. We also observe a thermal Hall conductivity similar to that observed by Kasahara et al. [1] and will provide updates on our attempts to verify the quantization. 
Monday, March 15, 2021 9:48AM  10:00AM Live 
A39.00008: Raman spectroscopy evidence for dimerization and Mott collapse in αRuCl_{3} under pressures Li gm We perform Raman spectroscopy studies on αRuCl_{3} at room temperature to investigate its phase transitions of magnetism and structure under pressure. The Raman measurements resolve two critical pressures at p_{1} = 1.1 GPa and p_{2} = 1.7 GPa with very different structural and magnetic behaviors. With increasing pressure, a stacking order phase transition of αRuCl_{3} occurs at p_{1}, indicated by the new Raman modes. The appearance of infrared active modes in Raman spectrum usually results from the inversion symmetry breaking, which is confirmed by the second harmonic generation measurement. The second transition at p_{2} is signaled by the inplane RuRu bond dimerization accompanied by the Mott collapse and the system becomes a correlated band insulator. Our studies demonstrate the competition among spinorbit coupling, magnetism, and chemical bondings in Kitaev compounds. 
Monday, March 15, 2021 10:00AM  10:12AM Live 
A39.00009: Tunneling spectroscopy of quantum spin liquids Elio Koenig, Mallika Randeria, Berthold Jaeck We examine the spectroscopic signatures of tunneling through a Kitaev quantum spin liquid (QSL) barrier in a number of experimentally relevant geometries. We combine contributions from elastic and inelastic tunneling processes and find that spinflip scattering at the itinerant spinon modes gives rise to a gapped contribution to the tunneling conductance spectrum. We address the spectral modifications that arise in a magnetic field which is applied to drive the candidate material αRuCl3 into a QSL phase, and we propose a lateral 1D tunnel junction as a viable setup in this regime. The characteristic spin gap is an unambiguous signature of the fractionalized QSL excitations, distinguishing it from magnons or phonons. We discuss the generalization of our results to a wide variety of QSLs with gapped and gapless spin correlators. 
Monday, March 15, 2021 10:12AM  10:24AM Live 
A39.00010: Bond directional anisotropy and Dzyaloshinskii–Moriya interaction induced metamagnetic state in honeycomb lattice magnet Tb_{2}Ir_{3}Ga_{9} Mojammel Alam Khan, Randy Fishman, Qiang Zhang, Feng Ye, John Mitchell Bond directional anisotropy (BDA), a key element in the Kitaev honeycomb lattice model for j_{eff} = ½ interacting spin system can enable spin liquid ground state with nonAbelian Majorana fermion as the low energy excitations. In this motif, several insulating materials, such as αRuCl_{3}, YbCl_{3}, and NaIrO_{3} are under intense study to observe the quantum entanglement. Recently, Tb_{2}Ir_{3}Ga_{9} where Tb atoms are arranged in a honeycomb lattice, were shown to exhibit substantial BDA in both inplane and out of plane directions as well as a finite DzyaloshinskiiMorya interaction (DMI) in crystallographic cdirection to stabilize the antiferromagnetic ground state. Mediated via RKKY interaction, conduction electron spectra are modified by the magnetism to exhibit steplike magnetoresistance (MR) in the metamagnetic transition regime. By applying current along the honeycomb lattice plane, signature of multiple thermodynamically equivalent metamagnetic state can be observed. Detailed MR and Hall effect measurements will be discussed to understand the evolution of magnetic ground state in present of BDA and DMI in the honeycomb lattice arrangement. 
Monday, March 15, 2021 10:24AM  10:36AM Live 
A39.00011: Phonon dynamics of Kitaev spin liquid at finite temperatures Kexin Feng, Mengxing Ye, Natalia Perkins When searching for quantum spin liquid physics in Kitaev materials, a general feature to look for is the fractionalization of spins into two types of quasiparticle excitations, which according to the exact solution of the Kitaev model [1] are localized, gapped Z2 fluxes and itinerant Majorana fermions. In pursuit of spin fractionalization, a lot of experimental and theoretical effort has been 
Monday, March 15, 2021 10:36AM  10:48AM Live 
A39.00012: Kitaev interactions in metallic bands and resulting Berry curvature distributions Wenjuan Zhang, Zachariah Addison, Nandini Trivedi The Kitaev spin model on a honeycomb lattice with competing bonddependent interactions describes a quantum spin liquid (QSL) with topological order and fractionalized excitations. Such models can be realized in Mott insulators withstrong spinorbit coupling. The main question we ask is: what is the manifestation of the bonddependent frustration in the opposite weakly correlated metallic limit? We investigate a symmetryallowed tight binding model on a honeycomb lattice with 5d t_{2g} orbitals (L_{eff}=−1) in the presence of strong atomic spinorbit coupling. We choose the parameters of this tightbinding model such that in the strong coupling limit it reproduces the Heisenberg and Kitaev spin Hamiltonians. We find that the band touching points move from K/K′, for the tightbinding parameters corresponding to the Heisenberg Hamiltonian, to M and Γ for the Kitaev parameters. Furthermore, for the Kitaev parameters, the frustration is reflected in extremely flat bands. We calculate the effect of the evolution of the Berry curvature on the linear and nonlinear electromagnetic response. 
Monday, March 15, 2021 10:48AM  11:00AM Live 
A39.00013: Magnetic Anisotropy in Spin3/2 with Heavy Ligand in Honeycomb Mott Insulators: Application to CrI_{3} Panagiotis Peter Stavropoulos, Xiaoyu Liu, HaeYoung Kee Ferromagnetism in the twodimensional CrI_{3} has generated a lot of excitement, and it was recently proposed that the spinorbit coupling in Iodine may generate bonddependent spin interactions leading to magnetic anisotropy. Here we derive a microscopic spin model of S=3/2 on transition metals surrounded by heavy ligands in honeycomb Mott insulators using a strongcoupling perturbation theory. For ideal octahedra we find the Heisenberg and Kitaev interactions, which favor the magnetic moment along the cubic axis via quantum fluctuations. When a slight distortion of the octahedra is present together with the spinorbit coupling, three additional terms, the offdiagonal symmetric interactions Γ and Γ', and onsite Ising interactions arise. They result in the magnetic anisotropy that pins the moment perpendicular to the honeycomb plane. Applications to single layer CrI_{3} are discussed. [1] 
Follow Us 
Engage
Become an APS Member 
My APS
Renew Membership 
Information for 
About APSThe American Physical Society (APS) is a nonprofit membership organization working to advance the knowledge of physics. 
© 2021 American Physical Society
 All rights reserved  Terms of Use
 Contact Us
Headquarters
1 Physics Ellipse, College Park, MD 207403844
(301) 2093200
Editorial Office
1 Research Road, Ridge, NY 119612701
(631) 5914000
Office of Public Affairs
529 14th St NW, Suite 1050, Washington, D.C. 200452001
(202) 6628700