Bulletin of the American Physical Society
APS March Meeting 2022
Volume 67, Number 3
Monday–Friday, March 14–18, 2022; Chicago
Session S51: Kagome & ShastrySutherland SystemsFocus Recordings Available

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Sponsoring Units: GMAG DMP Chair: Peter Armitage, Johns Hopikns Univ. Room: McCormick Place W474B 
Thursday, March 17, 2022 8:00AM  8:12AM 
S51.00001: Field Induced Spin Structure of Ising Shastry Sutherland Plateaus in Holmium Tetraboride Guga Khundzakishvili, Eliana Stoyanoff, Linda Ye, Yaohua Liu, Hayato UshijimaMwesigwa, Akshat Jha, Paul M Kairys, Travis S Humble, Joseph G Checkelsky, Arnab Banerjee Rare earth tetraborides are a class of ShastrySutherland magnets with frustrationgenerated magnetization plateaus in the Ising limit, but the microscopic origin of these plateaus is not fully understood. To elucidate these origins, we conduct neutron white beam Laue experiments on holmium tetraboride (HoTe4) and observe microscopic ordering and new inplane incommensurate orders not previously reported besides the conventional 1/3 plateau appearing from commensurate outofplane order. Determining the nature of these phases enables us to deduce the Hamiltonian and the exact frustration mechanisms that might lead to the rich magnetic phase diagram. We hypothesize the microscopic origins of these observations and confirm this hypothesis using classical computations. Especially, we discuss opportunities to interpret these experimental results using unconventional computing paradigms such as quantum and digital annealing. 
Thursday, March 17, 2022 8:12AM  8:24AM 
S51.00002: No Sign of Staggered Magnetization in the Recently Discovered Quantum Dimer Magnet  Yb_{2}Si_{2}O_{7} Andrew Treglia In 2019, Hester et al. reported Yb_{2}Si_{2}O_{7} as the first rareearthbased Quantum Dimer Magnet (QDM), with low temperature physics that can be traced back to a topic found in any quantum mechanics textbook: the interaction of two spin 1/2 particles subjected to a magnetic field. Many versions of the QDM have been studied with 3d transition metal species, showing a "BoseEinstein Condensation (BEC) dome" in the magnetic field vs. temperature phase diagram, where within the dome an antiferromagnetic order is established. Unlike these traditional QDM's the BEC dome for Yb_{2}Si_{2}O_{7} appears to contain two separate phases, however, previous experimental work has not directly observed the antiferromagnetic order in any region of the dome. Here we present elastic neutron scattering data as a function of magnetic field strength throughout the dome. This suggests either an issue with thermal equilibration, or that the size of the ordered moment within the dome is small due to quantum fluctuations. For the latter to be the case, additional anisotropic terms in the Hamiltonian are required. 
Thursday, March 17, 2022 8:24AM  8:36AM 
S51.00003: Anisotropic magnetism on the squarelattice, the case of Dybased oxyhalides David T Brooks, Xiaojian Bai, Stuart Calder, Vasile O Garlea, Martin P Mourigal Rareearth ions often display anisotropic magnetization distributions and are enticing in searching for exotic forms of magnetic matter. We present an investigation into the magnetic properties of a series of three DysprosiumOxyhalides (DyOX) compounds: DyOCl, DyOBr, and DyOI. These materials exhibit layered square lattices, with the primary difference between compounds being the interlayer spacing, which is dependent on the size of the halide ion. This structure allows for a frustrated J_{1}J_{2} model with tunable offdiagonal exchange interactions due to spinorbit on the ligands. Several forms of data have been analyzed, including xray diffraction, neutron scattering, and thermodynamic measurements such as heat capacity and magnetic susceptibility. Analysis of heat capacity reveals the presence of magnetic ordering below 7K with a secondary peak that occurs higher in temperature, which implies some additional ordering transition. We will discuss the origin of this peak and the unique magnetic behavior of these compounds. 
Thursday, March 17, 2022 8:36AM  9:12AM 
S51.00004: First principles generation of magnetic Hamiltonians and phase diagrams of frustrated magnets Invited Speaker: Harald O Jeschke Research in frustrated and complex magnetism has made enormous progress in recent years. Improved sample growing and experimental techniques have changed the focus from perfecting material realizations of single or few parameter kagome or triangular lattice model Hamiltonians to a wealth of materials with low symmetry, lattice distortions and complex threedimensional networks. Determining the magnetic Hamiltonian of such materials is often not feasible with simple fits to experimental data. However, an accurate density functional theory based energy mapping technique with statistical safeguards promises to be a step forward, allowing unbiased determination of completely nonintuitive hierarchies of exchange interactions. This will be illustrated with a number of recent examples. In the quest for quantum spin liquids, there are new fascinating possibilities to realize them in three dimensions: From five exchange couplings of equal rank in K_{2}Ni_{2}(SO_{4})_{3}, energy mapping shows that two trillium lattices are in competition with a strong bipartite lattice coupling and puts the material on the verge of a 3D quantum spin liquid (QSL) of nickel S=1 spins [1]. The DFT based method also identifies a highly frustrated hyperkagome network in PbCuTe_{2}O_{6} that explains the experimental QSL signatures [2]. In BaCoSiO_{4}, energy mapping identifies the cause for a complex magnetic order where the magnetic cobalt sites are partitioned into three entwined networks; together with tiny frustration and anisotropic interactions, this leads to a magnetic field control of toroidal moments [3]. In atacamite Cu_{2}Cl(OH)_{3}, the relevant Hamiltonian is impossible to guess due to the crystal distortion; it turns out that intricate 3D couplings of sawtooth chains can explain the magnetization dynamics [4]. For the distorted lattice of Ykapellasite Y_{3}Cu_{9}(OH)_{19}Cl_{8}, energy mapping identifies a three parameter kagome lattice Hamiltonian with a very interesting phase diagram [5]. 
Thursday, March 17, 2022 9:12AM  9:24AM 
S51.00005: Magnetic fluctuations with a small gap in a nearly perfect Kagome Heisenberg antiferromagnet revealed by thermal transport Christian Hess, XiaoChen Hong, Bernd Büchner, Yuesheng Li, Yuan Long, Boqiang Li Twodimensional Spin1/2 Kagome Heisenberg antiferromagnets are arguably the most promising model to realize quantum spin liquid state with geometric frustrations. Over the past decades, enormous work had been dedicated to one such material, the Herbertsmithite ZnCu_{3}(OH)_{6}Cl_{2} [1]. However, there is even no consensus on whether its spingap exists or not, partially due to the intrinsic disorder of Herbertsmithite crystals. Here we report on lowtemperature thermal conductivity of an alternative Kagome Heisenberg antiferromagnet YCu_{3}[OH(D)]_{6.5}Br_{2.5} (YCOB), which is free from the disorder problem [2]. YCOB is dominated by the nearest neighbor spin interaction of ~ 56 K, while no magnetic order was detected down to 2 K [2]. We found that its thermal conductivity is purely phononlike at the low temperature limit without a residual linear term, thus ruling out gapless spin excitations. However, at a temperature as low as 250 mK, the thermal conductivity deviates from the phononic powerlaw behavior, indicating scattering from spin excitations sets in. Furthermore, the spin excitation spectrum can be turned by magnetic fields. We propose a fieldclosing of the small spin gap in YCOB. 
Thursday, March 17, 2022 9:24AM  9:36AM 
S51.00006: Lowtemperature magnetic phase in novel Kagome superconductor RbV_{3}Sb_{5} Jonathan Frassineti, Giuseppe Allodi, Roberto De Renzi, Pietro Bonfà, Erick Garcia, Vesna F Mitrovic, Samuele Sanna, Rong Cong We present the lowtemperature phase diagram as inferred by microscopic nuclear magnetic resonance (NMR) measurements in a recently discovered material belonging to the class of Kagome superconductors [1], namely RbV_{3}Sb_{5}. This class of materials shows a ChargeDensity Wave (CDW) phase transition at a temperature T_{CDW} ≅ 80÷103 K [2], related to a 2×2×2 structural modulation. 
Thursday, March 17, 2022 9:36AM  9:48AM 
S51.00007: Magnon crystallization in the kagome lattice antiferromagnet Juergen Schnack We present numerical evidence for the crystallization of magnons 
Thursday, March 17, 2022 9:48AM  10:00AM 
S51.00008: Magnetism in a distorted kagome lattice: the case of Ykapellasite Aleksandar Razpopov, Max Hering, Francesco Ferarri, Igor Mazin, Roser Valenti, Harald O Jeschke, Johannes Reuther Compounds like the wellknown Herbertsmithite are examples of the ideal spin1/2 antiferromagnetic (AFM) kagome lattice which has one of the most interesting magnetic phase diagrams. However, while the perfect AFM kagome lattice has been extensively investigated, less is known about distorted kagome lattices. 
Thursday, March 17, 2022 10:00AM  10:12AM 
S51.00009: Universal scaling of the specific heat in $S=1/2$ quantum kagome antiferromagnet herbertsmithite Hinako Murayama, Takahiro Tominaga, Tomoya Asaba, Andre de Oliviera Silva, Yuki Sato, Hiroki Suzuki, Yuzuki Ukai, Shota Suetsugu, Yuichi Kasahara, Ryutaro Okuma, Itamar Kimchi, Yuji Matsuda The antiferromagnetic spin1/2 Heisenberg model on a kagome lattice is one of the most paradigmatic models in the context of quantum spin liquids (QSLs). However, the exact understanding of the kagome QSL nature has suffered from the lack of fundamental information, in particular thermodynamic properties of kagome layers. Through the specific heat and thermal conductivity measurements in magnetic fields with high resolution, here we investigated the intrinsic thermodynamic properties of singlecrystal herbertsmithite ZnCu$_3$(OH)$_6$Cl$_2$, a canonical candidate for bearing a QSL on a perfect kagome lattice. It is striking that the intrinsic magnetic specific heat contribution arising from the kagome layers exhibits excellent scaling collapse as a function of $T/H$ (temperature/magnetic field). In addition, no residual linear term in the thermal conductivity $\kappa/T(T\rightarrow 0)$ is observed in zero and applied magnetic fields, indicating the absence of itinerant gapless excitations. These results capture a new essential feature of the QSL state of the kagome layers; localized orphan spins induced by exchange bond randomness, surrounded by a nonitinerant QSL. 
Thursday, March 17, 2022 10:12AM  10:24AM 
S51.00010: Multiloop pseudofermion functional renormalization for quantum spin systems: Application to the spin1/2 kagome Heisenberg model Marc K Ritter, Julian Thoeniss, Fabian B Kugler, Jan Von Delft, Matthias Punk We present a multiloop pseudofermion functional renormalization group (pffRG) approach to quantum spin systems and its application to the spin1/2 Heisenberg model on the kagome lattice. At pure nearestneighbor coupling, the system shows indications for an algebraic spin liquid through slowerthanexponential decay with distance for the static spin susceptibility, while the pseudofermion selfenergy develops a pronounced lowenergy power law. Methodologically, the pseudofermion representation of spin models inherently yields a strongly interacting system, and the quantitative reliability of a truncated fRG flow is a priori unclear. We demonstrate convergence in loop order, which provides further evidence for the internal consistency of the approach through correspondence with the selfconsistent parquet equations. In the spinliquid phase, the multiloop flow remains stable as the infrared cutoff Λ is reduced down to below 1% of the microscopic exchange interaction J. We also scrutinize the pseudofermion constraint of single occupation per site, which is only fulfilled on average in pffRG. Although fluctuations in the occupation number are not entirely suppressed, we find that they do not affect the qualitative conclusions drawn from the spin susceptibility. 
Thursday, March 17, 2022 10:24AM  10:36AM 
S51.00011: OffDiagonal Symmetric Exchange on the Kagome Lattice Ciaran Hickey Recent years have seen a surge of interest in spinorbit entangled Mott insulators, largely driven by the tantalizing prospect of realising the physics of Kitaev's celebrated honeycomb model. However, there are also other distinct exchange interactions that can be generated in such Mott insulators, which come with their own unique physics and intriguing properties. Here, we focus on offdiagonal symmetric exchange on the kagome lattice. In the classical limit the model, with an antiferromagnetic sign, leads to classical spin liquid behavior. On the other hand, in the quantum spin1/2 limit, quantum fluctuations drive the system into an ordered ground state. We will discuss various elements of the classical and quantum limits using a variety of analytical and numerical techniques, shedding light on these new exchange models within the realm of quantum magnetism. 
Thursday, March 17, 2022 10:36AM  10:48AM 
S51.00012: SpinPeierls instabilities of the kagome lattice antiferromagnet Francesco Ferrari, Aleksandar Razpopov, Federico Becca, Roser Valenti The spin1/2 antiferromagnetic Heisenberg model on the kagome lattice is a cornerstone in the field of frustrated magnetism, standing out as one of the most explored magnetic models that could host a quantum spin liquid ground state [1]. The high degree of geometric frustration of the lattice leaves a footprint in the spectrum of the quantum system, which is densely populated by a myriad of singlet excitations, testifying the presence of several proximate competing phases at lowenergy, which may be favored by different perturbations. For this reason, we investigate the potential instability of the kagome spinliquid ground state towards valencebond order as a consequence of the coupling between spin degrees of freedom and lattice distortions, the latter being modeled by quantum phonons. Employing a recently developed variational Monte Carlo framework [2], we study a (fully quantum) spinphonon model on the kagome lattice, with an eye to recent experimental findings of structural distortions in the Herbertsmithite compound [3]. 
Thursday, March 17, 2022 10:48AM  11:00AM 
S51.00013: Magnetic structure of equilibrium, zerofield, and nonequilibrium infield phases in TmB4. Amirreza Hemmatzade, Tom Fennell TmB4 belongs to a family of metallic rare earth tetraborides in which the rare earth moments form an orthogonal dimer network corresponding to the 2D ShastrySutherland lattice (SSL). In the case of Tm3+ (J=6), the crystal field produces a pseudodoublet ground state with dominant mj=±6 components and large (6.6 μB) Isinglike magnetic moments. Competition between the RKKY and dipolar interactions on the SSL leads to three ordered phases in zero field and the emergence of fractional magnetization plateaus at 1/8 and ½ of the saturation magnetization. While the magnetization plateaus appear to be nonequilibrium effects, the structures that exist within them may well be related to those of the zerofield ordered phases. Here we present results of single crystal neutron diffraction to determine the magnetic structures of the zero field three phases, i.e. commensurate AFM phase with k=(1,0,0), lowtemperature incommensurate AFM phase ( k’=(1+delta,0,0)) and highertemperature incommensurate phase (k”=(1+delta,delta’,0)), and report on our efforts to investigate the outofequilibrium phases of TmB4 using neutron diffraction combined with insitu measurements of magnetization and dilatometry. 
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