Bulletin of the American Physical Society
APS March Meeting 2022
Volume 67, Number 3
Monday–Friday, March 14–18, 2022; Chicago
Session S67: Topology in Kagome LatticesFocus Recordings Available

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Sponsoring Units: DMP GMAG DCMP Chair: Michihiro Hirata, Los Alamos National Lab; Victor Lopez Dominguez, Northwestern Room: Hyatt Regency Hotel Hyde Park 
Thursday, March 17, 2022 8:00AM  8:36AM 
S67.00001: Electronic structure evolution in magnetic topological materials Invited Speaker: Madhab Neupane The discovery of topological insulators (TIs) has prompted intensive theoretical and experimental studies on realizing various topological states in quantum materials. Owing to the bulkboundary correspondence, the TIs support conducting surface states that lie within the gapped bulk electronic spectrum of the TIs. These surface states are spin polarized and disperse linearly with Diraccone energy dispersion. Constraints of the timereversal symmetry protect the surface states from backscattering and localization in the presence of nonmagnetic perturbations thereby making TIs promising for lowpower energyefficient quantum electronic applications. Recently, new types of topological materials inspired by magnetism have attracted intensive research interest. In this talk, I will discuss electronic structure evolution across the magnetic transition temperature for (1) a higher order topological material candidate, (2) rareearth monopnictide based materials, (3) a magnetically doped topological material and (4) kagome magnets. Our study indicates that magnetism plays an intricate role in the electronic structure of the topological material family. 
Thursday, March 17, 2022 8:36AM  8:48AM 
S67.00002: A Topological Kagome Magnet in High Entropy Form Lujin Min, Milos Sretenovic, Thomas W Heitmann, Rui Zu, Venkatraman Gopalan, Xianglin Ke, Zhiqiang Mao Topological kagome magnets RMn_{6}Sn_{6} (R = rare earth element) attract numerous interests due to their nontrivial band topology and roomtemperature magnetism^{[}^{1]}. On the other hand, increasing attention is focused on the magnetic properties of high entropy materials, as the coexistence of multiple magnetic elements is expected to generate unconventional complex magnetic orderings. However, the study on single crystalline high entropy topological magnets is still lacking. 
Thursday, March 17, 2022 8:48AM  9:00AM 
S67.00003: Spectroscopic tunability of kagome magnet Fe_{3}Sn_{2} thin films by magnetic field Zheng Ren, Shrinkhala Sharma, Hong Li, He Zhao, Bryan Rachmilowitz, Faranak Bahrami, Fazel Tafti, Shiang Fang, Madhav P Ghimire, Ziqiang Wang, Ilija Zeljkovic Kagome materials, named after the cornersharing hexagonal lattice structure, provide an excellent platform to study topological and correlated electronic states. Kagome magnet Fe_{3}Sn_{2} exhibits or has been theoretically predicted to exhibit many exotic quantum states, including flatbands, massive Dirac fermions, giant spinorbit tunability, helical nodal lines and switchable Weyl points. Among these phenomena, experimental evidence for the existence of switchable Weyl points has been difficult to achieve. We use molecular beam epitaxy to grow Fe_{3}Sn_{2} thin films and identify the Fe_{3}Sn_{2} phase from diffraction and magnetization measurements. Using scanning tunneling microscopy/spectroscopy, we observe multiple peaks in differential conductance (dI/dV) spectra around the Fermi level. The peaks disperse in energy when an outofplane magnetic field is applied. We discuss these observations in the context of Weyl points theoretically predicted to occur in this system in the vicinity of the Fermi level. 
Thursday, March 17, 2022 9:00AM  9:12AM 
S67.00004: Chemical doping studies on thin film antiferromagnetic kagome metal FeSn Minyong Han, Caolan John, Madhav P Ghimire, Shiang Fang, Manuel Richter, Hisashi Inoue, Efthimios Kaxiras, Joseph G Checkelsky Recent spectroscopic observation of Dirac and flat bands in transition metal stannide T_{m}Sn_{y} (T = Fe, Co) with high temperature magnetism has led to escalating excitement towards incorporating topological and correlated kagome materials into functional devices [1]. One of the main challenges along this path pertains to difficulty in attaining fully ondemand control over chemical potential and spin texture useful for versatile device operations. Here we report the systematic chemical doping studies on epitaxial thin films of antiferromagnetic kagome metal FeSn [2,3]. We present electrical and magnetic characterizations of samples across a wide range of doping concentration, temperature, and magnetic field. We interpret the results in light of twodimensional kagome band structures and their interlayer couplings. We also discuss the relevance of this work to spinbased information technologies including spinpolarized transport. 
Thursday, March 17, 2022 9:12AM  9:24AM 
S67.00005: Damped Dirac magnon in a metallic Kagome antiferromagnet FeSn Seunghwan Do, Koji Kaneko, Ryoichi Kajimoto, Kazuya Kamazawa, Matthew B Stone, Shinichi Itoh, Takatsugu Masuda, German D Samolyuk, Elbio R Dagotto, William Meier, Brian C Sales, Hu Miao, Andrew Christianson FeSn is a prototype Kagome magnetic metal exhibiting novel electronic properties. We report inelastic neutron scattering studies of the spin excitation spectrum of FeSn. The spectra display welldefined spin waves extending up to 120 meV. Above this energy, the spin waves become progressively broadened, reflecting interactions with the Stoner continuum. Using linear spin wave theory, we have determined an effective spin Hamiltonian that reproduces the measured dispersion at energies below the Stoner continuum. This analysis indicates that the Dirac magnon at the Kpoint remarkably occurs on the brink of a region where welldefined spin waves become damped. Our results emphasize the influential role of itinerant carriers on the topological spin excitations of metallic Kagome magnets 
Thursday, March 17, 2022 9:24AM  9:36AM 
S67.00006: Magnetic excitations and electronic structure of Kagome metal FeGe Xiaokun Teng, Ji Seop Oh, Ming Yi, Pengcheng Dai, JianXin Zhu, Kelly Neubauer, Lebing Chen, Bin Gao, Feng Ye, Garrett E Granroth, Aaron Bostwick, Eli Rotenberg, Christopher Jozwiak, Makoto Hashimoto, Donghui Lu, Robert J Birgeneau Twodimensional (2D) layered Kagome compounds are great platforms to study not only magnetic frustration but also topological phases that realize flat bands. It is predicted that the Kagome lattice can be constructed to realize flat band physics at 1/3 filling and quantum anomalous Hall effect mainly at 2/3 filling. Recently, a family of Kagome metals T_{m}X_{n} (T: Fe, Co, X: Sn,Ge, m:n = 3:1, 3:2, 1:1) has attracted much interests. Although flat bands and Dirac crossings are expected in the singleorbital nearestneighbor Kagome model, possible complications from evolution of the magnetic order and strong electronelectron interactions remain largely unexplored experimentally. Here I will present a new Kagome system  FeGe. Distinct from widely studied planar antiferromagnetic (AFM) FeSn (T_{N} = 365 K) and paramagnetic CoSn, it has a collinear caxis antiferromagnetic (AFM) structure between T_{N} = 410 K and T_{1} ~ 60 K, followed by an AFM spiral structure below T_{1} ~ 60 K. 
Thursday, March 17, 2022 9:36AM  9:48AM 
S67.00007: Ising ferromagnetic kagome metal TbV_{6}Sn_{6} Jonathan M DeStefano, Elliott W Rosenberg, JiunHaw Chu The synthesis and characterization of the vanadiumbased kagome metal TbV_{6}Sn_{6} is presented. A signature of a phase transition at 4.1K is observed in heat capacity, resistivity, and magnetic susceptibility measurements, and both resistivity and magnetization measurements exhibit hysteresis in caxis magnetic field. Furthermore, a strikingly large anisotropy in the magnetic susceptibility is observed, with the caxis susceptibility nearly 100 times the ab plane susceptibility at 2K. This is highly suggestive of uniaxial ferromagnetism, and the large size of 9.4μ_{B}/f.u. indicates the Tb^{3+} 4f electronic moments cooperatively align perpendicular to the Sn kagome lattice plane. The entropy at the phase transition is nearly Rln(2), indicating that the CEF ground state of the Tb^{3+} ion is a doublet, and therefore TbV_{6}Sn_{6} presents an ideal system to study the interplay between Ising ferromagnetism and nontrivial electronic states emerging from a kagome lattice. 
Thursday, March 17, 2022 9:48AM  10:00AM 
S67.00008: Tuning magnetism of ScMn_{6}Sn_{6} by Ga doping Richa Pokharel Madhogaria, Hasitha Wiranga Suriya Arachchige, Rui Xue, Shirin Mozaffari, Takahiro Matsuoka, David G Mandrus The presence of the Dirac and flat bands in Kagome materials has attracted much of the attention of materials scientists. Recently, RMn_{6}Sn_{6} (R= Sc, Y, and Rare Earths) materials that crystalize in the MgFe_{6}Ge_{6} structure have demonstrated exotic physics arising from the intraplanar ferromagnetic (FM) Kagome nets formed by Mnions. The magnetism in this class of materials exhibits ferrimagnetic, antiferromagnetic, and helical orderings. With our focus on tuning the magnetism of this class of compounds, we have synthesized ScMn_{6}Sn_{6} single crystals with Ga doping on the Sn sites. The temperature and fielddependent magnetization results show that a low doping concertation such as ~5 % can extend the helical phase up to 417 K from 370 K in the parent compound, while the increased doping concentration of 22 % suppresses the interplanar AFM correlations resulting in a ferromagnetic to paramagnetic transition at 370 K. The combination of magnetic and electrical transport measurements has been utilized to map out the magnetic phase as a function of Ga doping concentration. In our talk, we will discuss our attempt to understand the increase in the stability of the helical phase up to higher temperatures and finally reaching a ferromagnetic ground state with increasing Ga doping. 
Thursday, March 17, 2022 10:00AM  10:12AM 
S67.00009: Thermal conductivity of topological honeycomb ferromagnet CrGeTe_{3} Joshua Wakefield, Takashi Kurumaji, Takehito Suzuki, Joseph G Checkelsky Van der Waals magnet CrGeTe_{3} has been intensely studied as a layered ferromagnet with twodimensional honeycomb planes that hold potential for use in 2D magnetic devices and heterostructures. Additionally, recent neutron scattering experiments [1] have pointed toward the possibility that this system may host topological magnons in the magnetic excitation spectrum. Here, we present a thermodynamic study of CrGeTe_{3} including thermal conductivity measurements that supply evidence for an exceptionally strong spinlattice coupling within this material. We discuss further investigation that could corroborate and provide insight into the nature of topological magnetic excitations in this system. 
Thursday, March 17, 2022 10:12AM  10:24AM 
S67.00010: Engineer magnetic bilayer honeycomb with photonphonon interaction. Zexun Lin, Gregory A Fiete, Bowen Ma, Michael Vogl, Martin A Rodriguezvega Phononphoton interaction could be used to engineer magnetic system. A bilayer honeycomb lattice model is discussed. Phononphoton interaction is utilized here to generate interlayer DM interaction which leads to a noncollinear spin groundstate and a topological phase transition. We did a group thoery analysis on the phonon modes and spectrum calculations on magnon in the system. A transition from gapped magnon phase to topological magnon nodal line phase is analyzed. 
Thursday, March 17, 2022 10:24AM  10:36AM 
S67.00011: Tuning of Magnetism via Doping in Kagome Magnet YMn_{6}Sn_{6x}Ge_{x} Hari Bhandari, Peter Siegfried, Albert Davydov, Yanliu Dang, Nirmal Ghimire Kagome lattice magnets are an interesting class of materials as they host topological properties in their magnetic and electronic structures. YMn_{6}Sn_{6} is one such compound in which a series of competing magnetic phases is stabilized by applied magnetic field, and both an enigmatic topological Hall effect and a Dirac crossing close to the Fermi energy have been realized. This material also shows a magnetization induced Lifshitz transition and evidence of an efficient chargespin coupling in one of the magnetic phases, namely the fanlike phase. Tuning the magnetism, and thus the interplay with the electronic states, opens new avenues into precise control of the novel properties. Here, we demonstrate the extreme sensitivity of the magnetic phases in YMn_{6}Sn_{6x}Ge_{x }via magnetization and magnetotransport measurements. The high degree of sensitivity to small doping concentrations provides great potential for engineering the magnetic phases and associated electronic properties in this family of rareearth Kagome magnets. 
Thursday, March 17, 2022 10:36AM  10:48AM 
S67.00012: Thermodynamic evidence for a topological phase transition in a spin liquid state of αRuCl_{3} Yuichi Kasahara, Shota Suetsugu, Yuzuki Ukai, Masaki Shimomura, Hinako Murayama, Tomoya Asaba, Nobuyuki Kurita, Hidekazu Tanaka, Yuta Mizukami, Kenichiro Hashimoto, Takasada Shibauchi, Joji Nasu, Yukitoshi Motome, Yuji Matsuda Kitaev quantum spin liquid (QSL) displays the fractionalization of quantum spins into Majorana fermions. In magnetic field, the emergence of chiral Majorana edge modes leads to a halfinteger quantized thermal Hall conductance, which has been reported in the Kitaev candidate material αRuCl_{3} [14]. At high magnetic fields, the quantization disappears and the thermal Hall conductance κ_{xy} goes to zero rapidly, indicating a possible topological phase transition from the Kitaev QSL to a state without chiral Majorana edge modes. However, this phase transition, including its presence, is still elusive because an anomaly associated with the transition has not been clearly detected by thermodynamic quantities. Here we present the results of highresolution heat capacity measurements on αRuCl_{3} down to 200 mK. We find that the heat capacity exhibits a distinct anomaly at H ~ H*. H* is closed to the field where κ_{xy} vanishes. Along with the fact that the longitudinal thermal conductivity shows a discontinuous jump at H ~ H* [5], our results provide thermodynamic evidence for a firstorder topological phase transition in the spin liquid state of αRuCl_{3}. 
Thursday, March 17, 2022 10:48AM  11:00AM 
S67.00013: Impurity Effects in Spinon Majorana Materials Dushko Kuzmanovski, Ilya K Drozdov, Alexander V Balatsky Recently, magnonic materials have seen a rejuvenated interest in the context of the nontrivial topological band structure of magnonic excitations in materials that follows from a nonBravais crystal lattice. This nontrivial band structure has interesting signatures in various transport properties of magnon topological materials. In addition, the presence of Dirac points in the excitation spectrum leads to graphenelike impurity bound states. Here, we explore the extreme case of S=1/2 magnetic atoms with the most pronounced magnetic fluctuations and apply a familiar Majorana fermion representation, alternative to the usual HolsteinPrimakoff transformation applicable to the higherspin case. We obtain a selfconsistent meanfield fermionic description of these quantum magnets with fermionic excitations  spinons. For nonBravais lattices, such as the honeycomb lattice, we explore the band structure of the fermionic excitations  spinons, and their repercussions on impurity bound states and magnetic susceptibility. The system is readily amenable to quantum simulations using commercially available quantum processors. 
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