Bulletin of the American Physical Society
APS March Meeting 2023
Volume 68, Number 3
Las Vegas, Nevada (March 5-10)
Virtual (March 20-22); Time Zone: Pacific Time
Session T54: Kitaev and Honeycomb Systems |
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Sponsoring Units: GMAG Chair: Hitesh Changlani, Florida State University Room: Room 306 |
Thursday, March 9, 2023 11:30AM - 11:42AM |
T54.00001: Neutron scattering studies of the candidate Kitaev material Na2PrO3 Ryutaro Okuma, Roger D Johnson, Pascal Manuel, David J Voneshen, Radu Coldea Na2PrO3 has recently attracted attention as a candidate material to display unconventional magnetism associated with bond-dependent Kitaev interactions between effective spin-1/2 Pr4+ ions [1,2]. Here we report time-of-flight neutron diffraction, and inelastic neutron scattering measurements of the magnetic excitations, and discuss models for the magnetic ground state and spin Hamiltonian. [1] S.-H. Jang et al, Phys. Rev. B 99, 241106(R) (2019).[2] M. J. Daumet et al, Phys. Rev. B 103, L121109 (2021). |
Thursday, March 9, 2023 11:42AM - 11:54AM |
T54.00002: Neutron Scattering Study of a Co2+ Quantum Spin Liquid Candidate Material Tong Chen, Collin L Broholm, Chris J Lygouras Recently, a new generation of honeycomb materials based on the low spin 3d7 Co2+ has been proposed to host quantum spin liquids. We present an inelastic neutron scattering study of a low spin Co material that has originally attracted interest due to its potential to host quantum spin liquids. We identified a bipartite up-down magnetically ordered ground state on the honeycomb backbone of the system, that shows no sharp transitions in susceptibility or specific heat measurements. Observed spin excitations are broad in the reciprocal space in the 0 T field due to the geometric frustration, but spin waves develop under applied magnetic fields. We modeled the system using linear spin-wave theory and determined the exchange parameters. |
Thursday, March 9, 2023 11:54AM - 12:06PM Author not Attending |
T54.00003: μSR study of magnetism in Co-based honeycomb materials BaCo2(PO4)2 and BaCo2(AsO4)2 Megan R Rutherford, Dalmau Reig-i-Plessis, Alannah M Hallas
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Thursday, March 9, 2023 12:06PM - 12:18PM |
T54.00004: Geometrical frustration versus Kitaev interactions in BaCo2(AsO4) Emily Zhang, Thomas J Halloran, Félix Desrochers, Tong Chen, Li Ern Chern, Zhijun Xu, Barry Winn, Melissa K Graves-Brook, Matthew B Stone, Yiming Qiu, Alexander I Kolesnikov, Ruidan Zhong, Robert Cava, Yong-Baek Kim, Collin L Broholm Recently, Co-based honeycomb magnets have been proposed as promising candidate materials to host the Kitaev spin liquid state. One of the front-runners is BaCo2(AsO4)2 (BCAO), where it was suggested that the exchange processes between Co2+ ions via the surrounding edge-sharing oxygen octahedra could give rise to bond-dependent Kitaev interactions. In this work, we present and analyze comprehensive inelastic neutron scattering studies of BCAO with fields in the honeycomb plane. Combining the constraints from the magnon excitations in the high-field polarized state and the inelastic spin structure factor measured in zero magnetic field, we examine two leading theoretical models: the Kitaev-type JKΓΓ' model and the XXZ-J1J3 model. We show that the existing experimental data can be consistently accounted for by the XXZ-J1J3 model but not by the JKΓΓ' model, and we discuss the implications of these results for the realization of a spin liquid phase in BCAO and more generally for the realization of the Kitaev model in cobaltates. |
Thursday, March 9, 2023 12:18PM - 12:30PM |
T54.00005: Bond-dependent anisotropy and magnon breakdown in cobalt Kitaev triangular antiferromagnet Chaebin Kim, Sujin Kim, Pyeongjae Park, Taehun Kim, Jaehong Jeong, Seiko O Kawamura, Kenji Nakajima, Naoki Murai, Alexander L Chernyshev, Martin P Mourigal, Sung-Jin Kim, Je-Geun Park The Kitaev model, a honeycomb network of spins with bond-dependent anisotropic interactions is a rare example of a quantum spin liquid. Although most Kitaev model candidate materials eventually order magnetically due to inevitable non-Kitaev terms, their bond-dependent anisotropy manifests in unusual spin dynamics. It has recently been suggested that bond-dependent anisotropy can stabilize novel magnetic phases and exotic spin dynamics on the geometrically frustrated triangular lattice. Despite the tremendous interest in the synergy of geometric frustration and bond-dependent anisotropy, no example material has yet been found. Here, we report the existence of a frustrated triangular-lattice with bond-dependent anisotropy in the cobalt Kitaev triangular van der Waals antiferromagnet CoI2. This magnet exhibits substantial magnon breakdown and complex level repulsion in its momentum and energy-resolved spin dynamics, as measured by inelastic neutron scattering. A thorough examination of excitations in both the paramagnetic and magnetically ordered states revealed that the bond-dependent anisotropy is the origin of spiral order and magnon breakdown found in CoI2. Our result paves the way toward finding and understanding the Kitaev model with geometrical frustration. |
Thursday, March 9, 2023 12:30PM - 12:42PM |
T54.00006: Magnetic exchange Hamiltonian of the spin-helix material NiI2 from paramagnetic scattering and Possible Skyrmion Phase Olivia Vilella, Martin P Mourigal, Chaebin Kim, Je-Geun Park, Matthew B Stone Magnetic Van-der-Walls materials have experienced a surge of interest driven by the plethora of distinct magnetic phases that they can host and the possibilities to produce new artificial materials and interfaces with an eye towards applications. To maximize impact in this burgeoning area, it is necessary to understand the magnetic and electronic Hamiltonians of these systems in detail, including magnetic exchanges, charge gaps, transfer integrals, magnetic transition temperatures and associated structures, anisotropies, etc. The family of transition metal dihalides and trihalides MX2 and MX3 provides several Van-der-Walls materials with a large diversity of magnetic phases. A recent theoretical study points at nickel dihalide NiI2 as a likely realization of the Higher-Spin Kitaev triangular model due to ligand effects and strong Hund’s coupling at the nickel site, as well as a magnetic skyrmion phase from exchange and/or single ion anisotropy. In this talk we report inelastic neutron scattering measurements on NiI2 that uncover previously reported incommensurate magnetic Bragg peaks as well as diffuse and inelastic neutron scattering responses that are essential to understand the competing ferromagnetic and antiferromagnetic interactions in this compound. |
Thursday, March 9, 2023 12:42PM - 12:54PM |
T54.00007: Spin waves, order-by-disorder phenomena, and pseudo-Goldstone modes in MPX3 magnets Daniil S Antonenko, Jörn W Venderbos Layered honeycomb transition-metal trichalcogenides (MPX3) materials were recently studied in a number of experimental works and were shown to host a variety of zigzag and Neel magnetic orders. From a theoretical perspective, classical Luttinger-Tisza analysis of Heisenberg models for these materials leads to a large manifold of classically degenerate ground states. In our work we show how accounting for symmetry-allowed anisotropies and quantum fluctuations significantly lifts this degeneracy and gives rise to magnetic ordering via the order-by-disorder mechanism. We then calculate the spin wave spectrum in a number of relevant magnetic phases and analyze the corresponding soft modes. Remarkably, besides true Goldstone modes, we observe the appearance of pseudo-Goldstone modes, which appear due to the aforementioned accidental degeneracy at the classical level but acquire a small gap due to quantum effects. |
Thursday, March 9, 2023 12:54PM - 1:06PM |
T54.00008: Introduction of a New Complete-Exchange Honeycomb Layered Compound Faranak Bahrami, Oleg Lebedev, Sangyun Lee, Andrew J Woods, Xiaohan Yao, Roman Movshovich, Daniel Haskel, Fazel Tafti Kitaev spin liquid candidates have attracted considerable attention from the condensed matter community due to their desirable applications in the field of quantum computation. Obtaining a better understanding of their structural and thermodynamic properties, and gaining precise control over the synthesis in this family of materials, would grant access to their complex quantum nature. Here, I will introduce a new complete-exchange honeycomb layered material similar to Cu2IrO3. I will present the results of x-ray Rietveld refinement, transmission electron microscopy (TEM), and energy-dispersive x-ray spectroscopy (EDX) measurements to confirm the newly synthesized exchange compound is another example of a complete exchange reaction. Then, I will discuss the magnetic properties of the material as well as the heat-capacity data down to 85 mK. Although there is no clear sign of magnetic ordering in any of the measurements, the main source of this behavior will be discussed in the context of x-ray absorption spectroscopy (XAS) measurements. |
Thursday, March 9, 2023 1:06PM - 1:18PM |
T54.00009: Chiral Soliton Phases in Kitaev Spin Chains Erik S Sorensen The bond-dependent Ising interaction present in the Kitaev model has attracted considerable attention. The appearance of an unexpected intermediate phase under a magnetic field is particularly intriguing, and one may wonder if a similar phase occurs in Kitaev spin chains with alternating x- and y-bond Ising interactions. Previous studies have focused on a transverse field, hz, and reported a direct transition to the polarized state. Here, we investigate phase diagram with arbitrary angle of two longitudinal fields, hx and hy. For a magnetic field applied along the diagonal, hx=hy, the chain remains gapless up to a critical field hc1. Surprisingly, above hc1 it enters an unusual intermediate phase before reaching the polarized state at hc2. This phase is characterized by a staggered vector chirality and for periodic boundary conditions, a two-fold degeneracy with a finite gap. For open boundary systems the ground-state exhibits a single soliton, lowering the energy, and gapless excitations. However, the corresponding anti-soliton raises the energy sufficiently that a gap appears for soliton and anti-soliton pairs in periodic systems. We discuss an intuitive variational picture describing the soliton phase. |
Thursday, March 9, 2023 1:18PM - 1:30PM |
T54.00010: Field-Induced Kitaev Multipolar Liquid in d2 Honeycomb Mott Insulators Ahmed Rayyan, Derek Churchill, Hae-Young Kee Kitaev's spin-1/2 honeycomb model, featuring compass-like Ising interactions, has demonstrated the central role of bond-dependent frustration in generating exotic phases of matter. Such interactions appear naturally between the spin-orbit entangled dipole moments of several d5 and d7 Mott insulators, although the dominance of the Kitaev physics relative to other effects remains a topic of debate. Motivated by compass interactions among quadrupole moments in 5d2 Mott insulators, we provide a route to uncovering the Kitaev multipolar liquid, where it is the non-Kramers doublets carrying multipole moments that are fractionalized into Majorana fermions. The key ingredient is the magnetic field which allows for quadrupole-octupole interactions via mixing with the excited triplet states. The conditions to realize signatures of this phase in real materials are also discussed. |
Thursday, March 9, 2023 1:30PM - 1:42PM |
T54.00011: Competing Multipolar Orders and Field-induced Kitaev Multipolar Liquid in d2 Mott Insulators Derek Churchill, Hae-Young Kee, Ahmed Rayyan In 5d2 Mott insulators with strong spin-orbit coupling, the lowest pseudospin states form a non-Kramers doublet, which carries quadrupolar and octupolar moments. After a quick review on a microscopic model for various lattices with an edge-sharing octahedra geometry, featuring Ising octupolar and bond-dependent quadrupolar interactions, we present a way to reveal an octupolar order in the osmium double perovskites, Ba2BOsO6 (B=Mg,Cd, and Ca). We also discuss a model for these systems under an external magnetic field, which generates highly anisotropic, bond-dependent exchange interactions that depend on the field angle. The external field allows for quadrupole-octupole interactions, once forbidden by symmetry, via mixing with the excited triplet states and provides a microscopic route to uncover a Kitaev multipolar liquid. |
Thursday, March 9, 2023 1:42PM - 1:54PM Author not Attending |
T54.00012: Spin nematic, dimensional reduction, and chiral spin liquid in the S=1 Kitaev-Heisenberg model with biquadratic interactions Rico Pohle, Nic Shannon, Yukitoshi Motome The Kitaev model on the honeycomb lattice is an elegant realization of a quantum spin liquid, showing fractionalized excitations and topological order [1]. While it has been discussed mainly for materials with an effective spin-orbital entangled moment S=1/2 [2], theoretical studies suggest that the model could also be realized for S=1 or even larger S [3]. S=1 spin moments are special since they allow not only for dipolar but also quadrupolar fluctuations on a single site, which can lead to unconventional states, as seen, e.g., in spin nematic phases [4]. In this work, we show that the S=1 Kitaev model with bilinear-biquadratic interactions hosts many unconventional ordered and disordered phases. By using a global energy optimization scheme in combination with classical Monte Carlo simulations in the spin space U(3) [5], we obtain a comprehensive phase diagram offering quadrupolar, chiral, and dimensionally-reduced ordered phases, in addition to the known dipolar phases, i.e., the ferro, antiferro, zigzag, and stripy phases. Intriguingly, we find that the competition between the antiferromagnetic Kitaev and positive biquadratic interactions also promotes a noncoplanar chiral spin liquid at finite temperature. |
Thursday, March 9, 2023 1:54PM - 2:06PM |
T54.00013: Determining Kitaev interaction in spin-S honeycomb Mott insulators JIEFU CEN, Hae-Young Kee The Kitaev interaction in a honeycomb lattice with higher-spin S has been one of the central attractions, as it may offer quantum spin liquids. A microscopic theory showed that when the Hund's coupling at the transition metal generates S>1/2, the spin-orbit coupling at the heavy ligands provides a route to the Kitaev interaction. However, there have been debates over its strength compared to other symmetry-allowed interactions. Investigating the symmetry of the Hamiltonian for general S, we show the magnon energies at two momentum points related by a broken mirror symmetry reflect the Kitaev interaction when a magnetic field is in the mirror plane. Applying the symmetry analysis to CrI3 with S=3/2 together with the available angle-dependent ferromagnetic resonance data, we estimate the Kitaev interaction out of the full Hamiltonian and find that it is sub-dominant. Our theory can be tested by inelastic neutron scattering on candidate materials under the proposed magnetic field direction, which will advance the search for general S Kitaev materials. |
Thursday, March 9, 2023 2:06PM - 2:18PM |
T54.00014: Sound attenuation in the generalized Kitaev spin liquid susmita singh, Panagiotis Stavropoulos, Natalia Perkins Candidate materials for the Kitaev spin liquid generically have residual interactions beyond the Kitaev coupling. It therefore becomes necessary to understand how signatures of the quantum spin liquid, e.g., fractionalization of the spin excitations, are affected by the presence of these interactions. Recently it was shown that phonon dynamics is an indirect but effective probe to study fractionalized excitations in the Kitaev spin liquid. Ultrasound experiments can measure sound attenuation, which should show linear in temperature behavior if the scattering of phonons happens predominantly on Majorana fermions. So far the computation of the sound attenuation was only done in the pure spin-phonon coupled Kitaev model, without taking into account residual interactions. In order to understand experimental signatures, here we present a mean-field study of the sound attenuation in the generalized J-K-Γ model, which is relevant to candidate materials. Our findings show that as long as the system is in the spin liquid phase, characteristic features of the sound attenuation remain observable even in the presence of residual interactions. |
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