Bulletin of the American Physical Society
APS March Meeting 2020
Volume 65, Number 1
Monday–Friday, March 2–6, 2020; Denver, Colorado
Session A56: Kitaev Model Theory and Experiment 
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Sponsoring Units: DCMP GMAG Chair: Joseph Paddison, Oak Ridge National Lab Room: Mile High Ballroom 2C 
Monday, March 2, 2020 8:00AM  8:12AM 
A56.00001: Pressure Induced Quantum Spin Liquids in Extended Kitaev Model Jiucai Wang, ZhengXin Liu The Kitaev's Honeycomb lattice model has exactly solvable spin liquid ground states and has attracted lots of research interest. However, most Kitaev materials possess both Kitaev and nonKitaev interactions, resulting in magnetically ordered ground states. A possible way to suppress the magnetic order and to drive the system to quantum spin liquid phases is exerting high pressure, assuming that the bonddependent interaction strength can be adjusted by the external pressure. We illustrate this possibility by studying a (pressure caused) anisotropic spin model with variational Monte Carlo method. While the anisotropic pure Kitaev model contains only two phases, the presence of nonKitaev interactions result in a much richer phase diagram and give rise to several gapless spin liquids whose lowenergy spinon excitations contain different number of cones. We show that these gapless spin liquids can be distinguished experimentally. Furthermore, a small outofplane magnetic field opens a gap to these spin liquids and results in different chiral spin liquids, all of which are belonging to the Kitaev 16fold classification. 
Monday, March 2, 2020 8:12AM  8:24AM 
A56.00002: Transport and chaos in lattice SachdevYeKitaev models Haoyu Guo, Yingfei Gu, Subir Sachdev We compute the transport and chaos properties of lattices of quantum SachdevYeKitaev islands coupled by single fermion hopping, and with the islands coupled to a large number of local, low energy phonons. We find two distinct regimes of linearintemperature (T) resistivity, and describe the crossover between them. When the electronphonon coupling is weak, we obtain the “incoherent metal” regime, where there is nearmaximal chaos with front propagation at a butterfly velocity v_{B}, and the associated diffusivity D_{chaos} = (v_{B})^{2} /(2πT) closely tracks the energy diffusivity. On the other hand, when the electronphonon coupling is strong, and the linear resistivity is largely due to nearelastic scattering of electrons off nearly free phonons, we find that the chaos is far from maximal and spreads diffusively. We also describe the crossovers to low T regimes where the electronic quasiparticles are well defined. 
Monday, March 2, 2020 8:24AM  8:36AM 
A56.00003: Lowrank SachdevYeKitaev Models Jaewon Kim, Xiangyu Cao, Ehud Altman Motivated by recent works on atomcavity realizations of fast scramblers, and on Cooper pairing in nonFermi liquids, we study a family of solvable variants of the (q=4) SachdevYeKitaev model in which the rank and eigenvalue distribution of the coupling matrix J are tuneable. When the rank is proportional to the number of fermions, the low temperature behavior is sensitive to the eigenvalue distribution. We obtain a complete classification of the possible nonFermi liquid quantum phases. These include two previously studied phases whose fermion scaling dimension depends continuously on the rank; we show that they are maximally chaotic, but necessitate an extensively degenerate or negative semidefinite coupling matrix. More generic distributions give rise to "almost Fermi liquids'' with a scaling dimension Delta = 1/2, but which differ from a genuine Fermiliquid in quasiparticle decay rate, quantum Lyapunov exponent and/or specific heat. 
Monday, March 2, 2020 8:36AM  8:48AM 
A56.00004: Soft modes in the complex SachdevYeKitaev model Yingfei Gu, Alexei Kitaev, Subir Sachdev, Grigory Tarnopolsky We discuss soft modes in the SachdevYeKitaev model for complex fermions with large N flavors and a global U(1) charge. 
Monday, March 2, 2020 8:48AM  9:00AM 
A56.00005: Dynamical and thermal magnetic properties of the Kitaev spin liquid candidate αRuCl_{3} Pontus Laurell, Satoshi Okamoto αRuCl_{3} is a promising Kitaev spin liquid candidate, but orders magnetically, the description of which necessitates additional interaction terms. The nature of these interactions, their magnitudes and even signs, remain an open question. In this work we investigate dynamical and thermal magnetic properties of proposed effective Hamiltonians. We calculate T=0 inelastic neutron scattering (INS) intensities using exact diagonalization, and magnetic specific heat, C(T), using a thermal pure quantum states method. We find that no single current model satisfactorily explains all observed phenomena of αRuCl_{3}. In particular, we find that Hamiltonians derived from first principles can capture the experimentally observed hightemperature peak in C(T), while overestimating the magnon energy at q=0. In contrast, other models reproduce important features of the INS data, but do not adequately describe C(T). We propose a modified ab initio model that is consistent with both magnetic specific heat and lowenergy features of INS data. 
Monday, March 2, 2020 9:00AM  9:12AM 
A56.00006: Thermal and magnetoelastic properties of aRuCl_{3} in the fieldinduced low temperature states Rico Schoenemann, Shusaku Imajo, Franziska Weickert, Yasumasa Takano, Stephen E Nagler, David Mandrus, Marcelo Jaime Magnetocaloric effect, thermal expansion, and magnetostriction measurements on single crystal αRuCl_{3} samples in applied magnetic fields are discussed. αRuCl_{3} has been established as a promising candidate for the soughtafter physical realization of the Kitaev model, which describes S=1/2 spins on a honeycomb lattice with bond dependent Ising interactions, hosting Majorana fermions as well as a topological quantum spin liquid (QSL) ground state. Recent experimental data indicate signs of a QSL state that emerges in applied magnetic fields, once the antiferromagnetic (AFM) transition temperature T_{N} observed in zero field below 7K is suppressed. In order to identify the nature of the phase transitions below T_{N} and to map the phase diagram as a function of magnetic field, we conducted measurements of the magnetocaloric effect in pulse magnetic fields as well as thermal expansion and magnetostriction measurements in static fields up to 15 T. The results are discussed in the context of possible quantum critical and QSL behavior in αRuCl_{3}. 
Monday, March 2, 2020 9:12AM  9:24AM 
A56.00007: Multipartite Entanglement in the Kitaev Honeycomb Model James Lambert, Erik Sorensen Quantum spin liquid (QSL) phases of matter have proven extremely elusive from both experimental and theoretical perspectives. In the theoretical domain, examining the topological entanglement entropy has been a primary tool for diagnosing whether or not a model exhibits QSL physics in its groundstate. We study the Kitaev honeycomb model, a prototype of QSL physics in two dimensions, using the quantum Fisher information (QFI), which is both experimentally accessible and well defined at finite temperature. We explore he behaviour of the QFI in both the gapped and gapless phases and in the regions around the transition. 
Monday, March 2, 2020 9:24AM  9:36AM 
A56.00008: Spinone KitaevHeisenberg model on a twodimensional honeycomb lattice Xiaoyu Dong, Donna Sheng We study the KitaevHeisenberg model with a spin1 local degree of freedom on a twodimensional honeycomb lattice numerically by density matrix renormalization group method. We obtain the phase diagram with two spin liquid phases and four symmetry broken phases. We identify that the spin liquid is gapless and has shortranged spinspin correlations within the whole phase. Comparing to its spin1/2 counterpart, the spin1 spin liquid has more gapless modes. 
Monday, March 2, 2020 9:36AM  9:48AM 
A56.00009: Microscopic route to magnetic anisotropy in higherspin honeycomb lattice: application to CrI_{3} Panagiotis Peter Stavropoulos, HaeYoung Kee In the past decade transition metal (TM) compounds have generated a wealth of theoretical and experimental research on frustrated magnetism, especially TM compounds that host local 1/2 moments. Spinorbit coupling (SOC) of the TM cation sites plays a key role for the appearance and dominance of frustrated terms such as the Kitaev spin1/2 term. Very recently it has been recognized that SOC of the anion sites is a viable route to realizing frustrated higher spin model terms from superexchange paths [1]. We present the microscopic origin of frustrated S=3/2 model terms in d^{3} systems. The appearance and competition of the Kitaev term with conventional spin model terms are presented. Applications of the theory to CrI_{3} and related materials are also discussed. 
Monday, March 2, 2020 9:48AM  10:00AM 
A56.00010: TwoMagnon Bound States in the Kitaev Model in a [111]Field Subhasree Pradhan, Niravkumar Patel, Nandini Trivedi It is now well established that the Kitaev honeycomb model in a magnetic field along the [111]direction harbors an intermediate gapless quantum spin liquid (QSL) phase sandwiched between a gapped nonabelian QSL at low fields H<Hc_{1} and a partially polarized phase at high fields H>Hc_{2}. Here, we analyze the low field and high field phases and phase transitions in terms of single and twomagnon excitations using exact diagonalization (ED) and density matrix renormalization group (DMRG) methods. We find that the energy to create a bound state of twomagnons Δ_{p} becomes lower than the energy to create a single spin flip Δ_{s} near Hc_{2}. In the entire Kitaev spin liquid Δ_{p}<Δ_{s} and both gaps vanish at Hc_{2}. We make testable predictions for magnon pairing that could be observable in Raman scattering measurements on Kitaev QSL candidate materials. 
Monday, March 2, 2020 10:00AM  10:12AM 
A56.00011: Phase diagram of the spin1/2 KitaevGamma chain and emergent ``partial" SU(2) symmetry Wang Yang, Alberto Nocera, Tarun Tummuru, HaeYoung Kee, Ian Affleck We study the phase diagram of a onedimensional version of the Kitaev spin1/2 model with an extra ``$\Gamma$term", using analytical, density matrix renormalization group and exact diagonalization methods. Two intriguing phases are found. In the gapless phase, the low energy theory is described by an emergent SU(2)$_1$ WessZuminoWitten (WZW) model though the exact symmetry group is discrete. On the other hand, the relations between the local spin operators and the WZW currents and primary field contain SU(2) breaking coefficients. A modified nonabelian bosonization formula is proposed to capture such exotic emergent ``partial" SU(2) symmetry. In the ordered phase, there is numerical evidence for an $O_h\rightarrow D_8$ spontaneous symmetry breaking. 
Monday, March 2, 2020 10:12AM  10:24AM 
A56.00012: Ab initio quantum chemical study of magnetic interactions in the honeycomb KitaevHeisenberg systems Cu_{2}IrO_{3} and H_{3}LiIr_{2}O_{6} Mohamed Eldeeb, Ravi Yadav, Nikolay Bogdanov, Rajyavardhan Ray, Satoshi Nishimoto, Jeroen Van den Brink, Liviu Hozoi The magnetic interactions in honeycomb iridium oxide compounds are studied using quantum chemical wavefunctionbased methods. Mapping the results onto the corresponding effective spin model shows the crucial dependence of the anisotropic magnetic couplings, in particular Kitaev exchange, on the precise position of interlayer species and on additional geometrical factors such as IrOIr bond angles and IrO bond lengths. While the latter define the actual superexchange path between magnetic centers, the former may come into play through strong outofplane polarization of ligand 2p orbitals mediating intersite hopping [1,2]. 
Monday, March 2, 2020 10:24AM  10:36AM 
A56.00013: Kitaev material candidates beyond the Iridates Arun Ramanathan, Marcus Daum, Martin Mourigal, Henry S La Pierre Na2MO3 (M = a tetravalent metal) based Mott insulators have been studied recently as potential candidates to realize Kitaev spin model. 4d5 or 5d5 systems on a Honeycomb lattice exhibit spinorbit assisted Mott insulating ground states. At the strong SOC regime, the ground state for these ions in an octahedral crystal field is dominated by Jeff=1/2 states resulting in bonddependent anisotropic magnetic exchange in the plane, essential to realize the Kitaev spin model. However, candidates to realize the Kitaev spin model are not limited to 4d/5d systems. Lanthanide elements with significant SOC and inherent anisotropy can also be considered in this context. In this talk, I will present our work on a new lanthanidebased, Kitaev material candidate with a potential Jeff=1/2 ground state. Synthesis and structure of the material will be discussed. Physical property measurements coupled with inelastic neutron scattering results will be utilized to understand the singleion characteristics of the lanthanide and to unveil the rich lowtemperature physics of the material. 
Monday, March 2, 2020 10:36AM  10:48AM 
A56.00014: Ferrimagnetism and anisotropic phase tunability by magnetic fields in Na2Co2TeO6 Weiliang Yao, Yuan Li Na2Co2TeO6 is a honeycomblattice compound with a zigzag antiferromagnetic order [1,2]. It has recently been proposed to be a Kitaevlike magnet based on highspin d7 electron configuration [3,4]. To assess how close it is to realizing Kitaev quantum spin liquids, we have measured magnetization and specific heat on highquality single crystals in magnetic fields applied along highsymmetry directions [5]. With small training fields, we find a canonical ferrimagnetic behavior below 27 K, which reveals additional Neeltype order of canted moments. Moreover, moderate fields in the honeycomb plane can suppress the thermal transition at 27 K, and seem to partly reverse the momentcanting when applied perpendicular to the zigzag chains. In contrast, outofplane fields leave the transition largely unaffected, but promotes another transition below 10 K, possibly also related to canting reversal. Our study indicates the magnetism of Na2Co2TeO6 is highly anisotropic and close to tipping points between competing phases. 
Monday, March 2, 2020 10:48AM  11:00AM 
A56.00015: magnetic structures and excitations in the series of A2PrO3 (A: alkali metals) mergen tunggiya, Kemp Plumb

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