Bulletin of the American Physical Society
APS March Meeting 2024
Monday–Friday, March 4–8, 2024; Minneapolis & Virtual
Session S22: Quantum Spin Liquids III: Triangular and Honeycomb SystemsFocus

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Sponsoring Units: GMAG Chair: Natalia Perkins, University of Minnesota Room: 101B 
Thursday, March 7, 2024 8:00AM  8:36AM 
S22.00001: Probing shortrange magnetism in candidate quantum spin liquids and related materials with a "bothand" approach to diffuse neutron scattering data Invited Speaker: Benjamin A Frandsen Extracting the maximum possible information from diffuse neutron scattering data is an important objective that supports efforts to gain a deeper understanding of the entangled ground states of quantum spin liquids and related materials. Significant progress has been made in the recent past by modeling diffuse magnetic scattering either in reciprocal space or real space using either bigbox (e.g. reverse Monte Carlo) or smallbox (e.g. magnetic unit cell) models. However, this "eitheror" approach may not be as effective as a "bothand" approach that considers the data in both reciprocal space and real space and makes use of both bigbox and smallbox models in a complementary fashion. The power of the "bothand" approach is highlighted in recent studies of two triangular lattice antiferromagnets: TmMgGaO_{4}, which is thought to host a KosterlitzThouless phase, and NaYbO_{2}, a candidate quantum spin liquid. We present diffuse neutron scattering data on both of these systems and demonstrate how the use of complementary modes of analysis reveals important details about the local magnetic correlations that could otherwise be easily missed. In addition to shedding light on the physics of these two interesting systems, this work motivates future "bothand" studies of candidate quantum spin liquids and related materials. 
Thursday, March 7, 2024 8:36AM  8:48AM 
S22.00002: New Quantum Spin Liquid Candidates Based on a Tm triangular lattice Karthik Rao, Bin Gao, Gregory T McCandless, Julia Y Chan, Pengcheng Dai, Emilia Morosan Quantum spin liquids are exotic states of matter where the electron spins are highly entangled but do not display any longrange magnetic order even at zero temperature. They contain fractionalized excitations and could lead to hightemperature superconductivity as well as applications in quantum computation. Therefore, the experimental realization of quantum spin liquids has been a longsought goal of condensed matter physics. Several triangular lattice rare earth compounds have been proposed as quantum spin liquid candidates thus far. The rare earth ions in these compounds have small spins and form a triangular lattice which can lead to exotic ground states due to geometric frustration brought about by the lattice symmetry. In this talk, I will discuss our results from single crystal thermodynamic measurements (fielddependent heat capacity, magnetization, ac susceptibility) and powder inelastic neutron scattering measurements on Tmbased triangular lattice compounds. No longrange order is observed down to 50 mK. The magnetic susceptibility indicates a high degree of frustration with a CurieWeiss temperature of 14 K. These are all indications of a quantum spin liquid ground state. 
Thursday, March 7, 2024 8:48AM  9:00AM 
S22.00003: How many bodies are manybody? Characterizing the effect of lattice sizes on manybody entanglements through thermal conductivity measurements on NaYb_{x}Lu_{1x}Se_{2} Yuanqi Lyu, Luke S Pritchard Cairns, Kenneth Ng, Chunxiao Liu, James G Analytis Quantum spin liquid (QSL) is an intriguing manybody phase of matter characterized by its anomalously high degree of entanglement. While new crystal candidates hosting QSL are synthesized continually, in recent years, simulating QSLs with Rydbergatomarraybased quantum simulators [Semeghini 2021] has gained considerable momentum. To characterize such an inherently manybody phase as QSL, infinitely large lattices of perfect geometric order are needed theoretically. In experimental practices, however, quantum simulators are limited to a few hundred sites, and lattice disorders are inevitable in crystal growths. Both limitations could drastically alter the intended QSL phases simulated or hosted [de la Torre 2023]. Therefore, it is crucial to investigate how lattice size and boundary conditions would affect the formation of QSL, attempting to answer the fundamental question of “how many bodies are manybody?” To do this, we synthesized compositions of NaYb_{x}Lu_{1x}Se_{2}, where by increasing the doping x, we can form a collection of antiferromagnetic triangular lattices of Jeff = 1/2 Yb^{3+} ions with growing sizes and connections. We then characterize this series via thermal transport measurements under extremely low temperatures, focusing on the behavior changes across the percolation transition at x = 0.5 when isolated lattices join to form networks of infinity size. 
Thursday, March 7, 2024 9:00AM  9:12AM 
S22.00004: Room temperature excitation continuum in the RareEarth Magnetic Insulator RInO_{3} Taek Sun Jung, Xianghan Xu, Jaewook Kim, Beom Hyun Kim, Hyun Jun Shin, Young Jai Choi, EunGook Moon, SangWook Cheong, Jae Hoon Kim Mott insulators have the capacity to support various unique ground states, and one of the most intriguing systems among them is a quantum spin liquid that comprises highly entangled spins. It is established that such an entangled system can host novel nonlocal excitations, like the continuum excitation known as a spinon. Using terahertz timedomain spectroscopy, we have detected a continuum excitation in the magnetic insulators RInO_{3} (where R stands for Tb^{3+} and Gd^{3+}). This continuum excitation exhibits optical conductivity proportional to the square of frequency, even at room temperature. Furthermore, a Fano distortion observed in the lowest optical phonon mode suggests a pronounced interaction with the continuum excitation. In the case of TbInO_{3}, the proportional frequencydependent optical conductivity remains robust and is unaffected by external magnetic fields of up to 7 T, persisting at low temperatures as low as 1.5 K. Conversely, the continuum excitation in GdInO_{3} diminishes as the temperature decreases. Our results propose the existence of an emergent charge excitation, even in a widebandgap Mott insulator, and hint at the potential for achieving a highly entangled manybody state at room temperature. 
Thursday, March 7, 2024 9:12AM  9:24AM 
S22.00005: Firstprinciples derivation of magnetic interactions in the triangular quantum spin liquid candidates KYbCh_{2} (Ch=S, Se, Te) and AYbSe_{2} (A=Na, Rb) John W Villanova, Allen O Scheie, Alan Tennant, Satoshi Okamoto, Tom Berlijn The AYbCh_{2} (A=alkali metal, Ch=chalcogen) delafossites hold great promise for the realization of the triangular quantum spin liquid state because of their defectminimized growth and lack of magnetic ordering down to extremely low temperature. Here we use ab initio computations and strong coupling perturbation theory to evaluate the exchange couplings of the delafossites and examine the influence of chemical substitution on promoting the development of a quantum spin liquid state. 
Thursday, March 7, 2024 9:24AM  10:00AM 
S22.00006: Bonddependent anisotropy and magnon decay in cobaltbased Kitaev triangular antiferromagnet Invited Speaker: Chaebin Kim The Kitaev model, a honeycomb network of spins with bonddependent anisotropic interactions, is a rare example that gives the quantum spin liquid state as an exact solution. Although most Kitaev model candidate materials eventually order magnetically due to additional nonKitaev interactions, their bonddependent anisotropy manifests in unusual spin dynamics. It has recently been suggested that bonddependent anisotropy can stabilize exotic magnetic phases on the geometrically frustrated triangular lattice. Unfortunately, few materials have been identified with simultaneous geometric frustration and bonddependent anisotropy. In this talk, I will present spin dynamics of iodinebased van der Waals triangular antiferromagnet CoI_{2}. We found evidence of finite bonddependent anisotropy in CoI_{2} using inelastic neutron scattering. From the paramagnetic scattering and observed magnetic structure, we conclude that the Kitaev interaction plays an essential role in explaining. Moreover, momentum and energyresolved inelastic neutron scattering measurements show substantial magnon decay and level repulsion in CoI_{2}. Our results provide the basis for future studies of the interplay between Kitaev magnetism and geometric frustration. 
Thursday, March 7, 2024 10:00AM  10:12AM 
S22.00007: Ab initio study for heterostructures of a Kitaev magnet αRuCl_{3} and CrX_{3} (X=Cl and I) Lingzhi Zhang, Yukitoshi Motome The Kitaev model is a honeycomb spin model with bonddependent anisotropic interactions, whose ground state features a quantum spin liquid with fractional excitations. Beyond the theoretical interest, it has also attracted much attention for the feasibility in real materials toward topological quantum computing. However, it remains a challenge to materialize the Kitaev spin liquid, especially at zero magnetic field, due to parasitic interactions beyond the Kitaev model. For instance, a prime candidate αRuCl_{3} exhibits a zigzagtype antiferromagnetic order at low temperature, albeit the hallmarks of the Kitaev spin liquid were observed only within a specific region in an applied magnetic field. Here, we propose a possible realization of the Kitaev spin liquid at zero field, by making van der Waals heterostructures of αRuCl_{3} and a ferromagnet CrX_{3} (X=Cl and I). Using ab initio calculations, we find that in the case of X=Cl, the spinorbit coupled Mott insulating state, which is a key to realizing the Kitaevtype interactions, is preserved in the heterostructure and the zigzag order is suppressed at zero field by the proximity of the XY ferromagnet CrX_{3}. In contrast, in the case of X=I, the Mott gap is almost closing, suggesting that the αRuCl_{3} layer is on the verge of an insulatormetal transition in the spinorbit coupled bands. Our results indicate that van der Waals heterostructures provide a new platform for studying not only magnetic but also electronic properties of the Kitaev spin liquids. 
Thursday, March 7, 2024 10:12AM  10:24AM 
S22.00008: Topological and magnetic phase transitions in bilayer KitaevIsing model Aayush Vijayvargia, Urban F Seifert, Onur Erten We investigate the phase diagram of a bilayer Kitaev honeycomb model with Ising interlayer interactions via Majorana mean field theory and perturbative analysis. We show that a diverse array of magnetic and topological phase transitions occur with interlayer exchange depending on the direction of the Ising interaction and the relative sign of the Kitaev interactions. When two layers have the same sign of the Kitaev interaction, a firstorder transition from a Kitaev spinliquid to a magnetically ordered state takes place. The magnetic order points along the Ising axis and it is (anti)ferromagnetic for (anti)ferromagnetic Kitaev interactions. However, when two layers have opposite sign of the Kitaev interaction, we observe a notable weakening of the magnetic tendencies and the Kitaev spin liquid survives up to a remarkably larger interlayer exchange. Our analysis identifies the emergence of an intermediate gapped Ζ_{2} spin liquid state, which eventually becomes unstable upon vison condensation. The confined phase is described by a highly frustrated 120° compass model. We conclude with a discussion on the perturbative analysis when the Ising axis lie along zaxis or in the xyplane. In both cases, our analysis reveals the formation of 1D Ising chains, which intriguingly remain decoupled up to the sixth order in perturbation theory. Our results highlight the interplay between topological order and magnetic tendencies in bilayer quantum spin liquids. 
Thursday, March 7, 2024 10:24AM  10:36AM 
S22.00009: Groundstate phase diagram of an extended KitaevGamma model on a honeycomb lattice Takafumi Suzuki, Matthias Gohlke, Jose C Pelayo Abstract: AlphaRuCl3 has been studied extensively due to the possible realization of Kitaev spin liquid physics. The KitaevGamma (KGamma) model on the honeycomb lattice has been proposed as a minimal model of alphaRuCl3. So far, the KGamma model has mostly been studied considering equal coupling strength along the three bond directions of the honeycomb lattice. However, the details of the ground states have been under debate. In this study, we extended the model to include an additional parameter that controls the coupling strength on one of the bonds; we connect the limit of isolated KGamma chains to the isotropically interacting twodimensional (2d) model. We investigate the groundstate phase diagram by using numerical exact diagonalizations and densitymatrix renormalization group methods. We find that TLL appearing in the chain limit [2] persist for finite interchain couplings. In this proximate TLL phase, the lowenergy excitation is characterized by spinonlike gapless excitation that is similar to that is observed in S=1/2 antiferromagnetic Heisenberg chain. In contrast, D4 magnetically ordered state [2] in the spin chain limit becomes 90degree noncoplanar ordered state in the 2d model. Furthermore, we find that two magnetically ordered states seem to exist near the limit of the antiferromagnetic Kitaev spin chain. These two states also become corresponding ordered states in the 2d model. 
Thursday, March 7, 2024 10:36AM  10:48AM 
S22.00010: Exotic Spin Liquid phases in Generalized Kitaev JKΓΓ' model on honeycomb lattice PoHao Chou, ChungYu Mou, Sungkit Yip, ChungHou Chung Employing a gauge invariant Majorana fermion decomposition of spin, we derive a renormalized meanfield theory (RMFT) for the Generalized Kitaev JKΓΓ' model under magnetic fields on a honeycomb lattice. We allow for the most general mean field parameters permitted by the projected symmetry group. Our RMFT approach provides good results compared with other numerical methods such as DMRG and VMC on the same model, e.g., reproducing the 8,14,20cone quantum spinliquid (QSL) states in the KΓmodel and under fields. Therefore, we are confident that this RMFT approach provides an economic way to investigate the meanfield spinon band structure properties (Chern number etc.) and complex vortices structure in JKΓΓ' model under field in arbitrary directions. 
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