Bulletin of the American Physical Society
APS March Meeting 2022
Volume 67, Number 3
Monday–Friday, March 14–18, 2022; Chicago
Session N72: MnTe Magnetic Topology IVRecordings Available

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Sponsoring Units: DMP GMAG DCMP Chair: Seong Joon Lim, Rutgers; Liqin Ke, Ames Lab Room: Hyatt Regency Hotel Jackson Park D 
Wednesday, March 16, 2022 11:30AM  11:42AM 
N72.00001: Strong MagnetoElastic Coupling in Mn_{3}X (X = Ge, Sn) revealed by Ultrasound Florian Theuss, Sayak Ghosh, Taishi Chen, Satoru Nakatsuji, Brad J Ramshaw The chiral antiferromagnets Mn_{3}X (X = Sn, Ge) have recently attracted a large amount of attention due to their large anomalous Hall response at room temperature, linked to Weyl nodes close to the Fermi surface. Besides manipulation of the Hall angle with small magnetic and electric fields, the sign of the Hall voltage has been demonstrated to switch under hydrostatic and uniaxial pressure. Here, we perform Resonant Ultrasound Spectroscopy (RUS) and Pulse Echo Ultrasound measurements to further investigate strong magnetoelastic coupling in Mn_{3}X. We observe giant anomalies in the compressional elastic constants, related to a large change of Neel temperature with hydrostatic pressure. Additionally, we extract a sizeable piezomagnetic coefficient in Mn_{3}Ge, made possible through the unique combination of irreducible representations of inplane shear strain and magnetic order parameter in Mn_{3}X. By examining the critical divergence of the bulk modulus close to the phase transition, we were able to place Mn_{3}Ge in the 3DXY universality class. Further, access to the shear modulus c_{66} offers the rare opportunity to extract the critical exponent for the nematic susceptibility. 
Wednesday, March 16, 2022 11:42AM  11:54AM 
N72.00002: Ultrafast phononmediated melting of magnetism via itinerant spins in MnBi_{2}Te_{4} John W Freeland, Hari Padmanabhan, Vladimir A Stoica, Peter K Kim, Maxwell Poore, Tiannan Yang, Xiaozhe Shen, Alexander Reid, MingFu Lin, Huaiyu Wang, Nathan Koocher, Danilo Puggioni, SengHuat Lee, Aaron M Lindenberg, Zhiqiang Mao, James M Rondinelli, Xijie Wang, LongQing Chen, Richard D Averitt, Venkatraman Gopalan A comprehensive understanding of spins away from equilibrium, including their interplay with lattice and electronic excitations is key to achieving fundamental breakthroughs in understanding how to manipulate topological phases with light. To this end, we study the ultrafast melting of magnetic order in the layered antiferromagnetic topological insulator MnBi_{2}Te_{4}. Here we use a multimodal experimental approach with ultrafast electron diffuse scattering to probe of nonequilibrium phonon dynamics, and magnetooptic Kerr rotation and resonant soft Xray scattering are used to directly measure ultrafast dynamics of conduction and localized spins. Our experiments reveal that ultrafast demagnetization occurs through a previously unidentified plike itinerant spin subsystem, with optical phonons acting as the primary channel for the dissipation of spin angular momentum. Localized Mn 3d^{5} spins disorder by a distinct, much slower thermalization mechanism, due to the quenched orbital angular momentum. The disparate demagnetization timescales in both spin subsystems provides evidence of a strong exchange coupling between the 3d localized spins and the plike itinerant bands, which sheds light on the interatomic exchange pathways that enable magnetic topological phases. 
Wednesday, March 16, 2022 11:54AM  12:06PM 
N72.00003: Magneto thermal conductivity and thermal Hall conductivity of single crystal MnBi through the spinreorientation temperature range Brandi L Wooten, Nuria Bagues Salguero, Bin He, Brian C Sales, David W McComb, Joseph P C Heremans The search for an experimental signature in transport properties of magnetic topological materials is a major thrust in materials research. MnBi, a hard hexagonal ferromagnet with a high Curie temperature and strong spinorbit interactions, is a great candidate to investigate this due to two properties. First, it has a unique spin reorientation (SR) behavior: under about 90 K the spins align in the abplane, above about 140 K the spins align along the caxis, and in between 90 and 140 K the spins have some degree of freedom between these two extremes.^{1} Second, it has an extremely large anomalous Nernst conductivity that is not simply explained by the band structure.^{2} Here, we explore the magneto thermal conductivity and thermal Hall conductivity of MnBi and study the structure and topology of the domains using Lorentz Transmission Electron Microscopy to identify the correlation between thermal transport properties and the topological properties of the domains in the SR regime. We show that the domain growth in an applied magnetic field causes a large decrease in magneto thermal conductivity and interesting trends in thermal Hall conductivity; however, this process is complex in the SR temperature regime. 
Wednesday, March 16, 2022 12:06PM  12:18PM 
N72.00004: Noncoplanar Magnetism in Mn_{3}Sn Youzhe Chen, Jonathan Gaudet, Joerg Strempfer, Satoru Nakatsuji, Collin L Broholm The magnetizationfree anomalous Hall effect of Mn_{3}Sn yields topological nontrivial bands with Weyl nodes at the Fermi level. Yet the knowledge of its incommensurate phase remains insufficient. Considering incommensurate magnetism itself historically manifests strong electron correlations in unconventional superconductors and heavy fermion systems, studies on the incommensurate magnetism of Mn_{3}Sn provides further insights of the itinerate electrons in Mn_{3}Sn. With neutron scattering techniques, we were able to fully determine the incommensurate magnetic structure and analyze its dynamics. Our results show potential strong correlation and competing interactions in the magnetic Weyl semimetal Mn_{3}Sn. 
Wednesday, March 16, 2022 12:18PM  12:30PM 
N72.00005: Magnetic and magnetoelectric transport properties of TbMn_{6}Sn_{6} thin films Qianheng Du, Deshun Hong, Changjiang Liu, Brandon Fisher, John Pearson, Anand Bhattacharya The kagome lattice is an excellent model system for studying frustrated magnetism, electronic correlation and topological electronic structure. Recently, quantum oscillations and the anomalous Hall effect in singlecrystals of the kagome compound TbMn_{6}Sn_{6} hint at the realization of a quantumlimit twodimensional Chern phase. We have synthesized epitaxial TbMn_{6}Sn_{6} thin films using molecular beam epitaxy. We have characterized the magnetization, magnetoresistance, and anomalous Hall effects of these thin films, and compare our results to those reported for bulk singlecrystals in the literature. The realization of highquality TbMn_{6}Sn_{6} thin films may present new possibilities in the search for topological quantum phenomena in kagome metals. 
Wednesday, March 16, 2022 12:30PM  12:42PM 
N72.00006: Ab initio studies of electronic structures and magnetic properties in RMn_{6}Sn_{6} (R =Gd, Tb, Dy, Ho, and Er) Ralph Skomski, Xindong Wang, Arjun K Pathak, Bruce Harmon, Robert J McQueeney, Liqin Ke Using ab initio methods, we systematically investigate the electronic structures and intrinsic magnetic properties in RMn_{6}Sn_{6} with R = Gd, Tb, Dy, Ho, and Er. The calculations show that TbMn_{6}Sn_{6} has an easyaxis anisotropy, DyMn_{6}Sn_{6} and HoMn_{6}Sn_{6} have easycone anisotropy, and ErMn_{6}Sn_{6} has an easyplane anisotropy, all agreeing well with experiments and explained by the Mn coordination of the rareearth atoms. The Mn sublattice is found to have an easyplane anisotropy of similar amplitude in all RMn_{6}Sn_{6} compounds. Band structures of various RMn_{6}Sn_{6} compounds share great similarities near the Fermi level as they mostly consist of non4f bands. Multiple Dirac crossings occur at the Brillouin zone corners and are opened by spinorbit coupling; most of them are strongly K_{z}dependent. The most prominent 2Dlike (barelyK_{z}dependent) Dirac crossing at K lies 0.6–0.7 eV above the Fermi level. However, additional onsite correlations within Mnd electrons can have profound effects on crossing energies and gap sizes. Finally, we discuss the effects of spin reorientation and the effects caused by the surface on the topological band structures. 
Wednesday, March 16, 2022 12:42PM  12:54PM 
N72.00007: Magnetization compensation temperature and frustrationinduced topological defects in ferrimagnetic antiperovskites Temuujin Bayaraa, Changsong Xu, Laurent Bellaiche, Sinead Griffin Antiperovskites can display promising properties such as superconductivity [1] and topological band gaps [2–4]. Ferrimagnets can have many promising features, such as a socalled magnetization compensation temperature (at which the total magnetization vanishes, as a result of cancellation between magnetic moments of different sublattices) and the perpendicular magnetic anisotropy which allows robust and ultrasmall skyrmions at room temperatures [5–7]. Such features make antiperovskite ferrimagnets very promising candidates for realizing highdensity, lowcost, and energyefficient skyrmionic device technology. 
Wednesday, March 16, 2022 12:54PM  1:06PM 
N72.00008: Anomalous Exchange Resonance Driven by SpinOrbit Torques in Intrinsic Antiferromagnetic Topological Insulator Junyu Tang, Ran Cheng In antiferromagnetic topological insulator MnBi2Te4, the interplay between topological electrons and magnetization dynamics in the form of spin torques and charge pumping remains an open question. Using the Berry phase theory, we develop a universal formalism to quantify the spinorbit torques (SOTs) and their reciprocal effects in layered MnBi2Te4, where the symmetry of SOTs exhibits an evenodd layernumber pattern. The dynamical consequences of our finding are demonstrated by the SOTdriven magnetic resonances. In particular, we identify an anomalous exchange (AE) mode in the triseptuple layer (SL) case, where the magnetic moments from the top and bottom SL rotate with a pi phase difference while those in the middle SL stay static. Unlike the ordinary exchange mode and the acoustic mode, the AE mode does not react to a microwave electromagnetic field. Therefore, the AE resonance can only be excited by the peculiar SOTs we find, providing a unique way to verify the SOTs in MnBi2Te4. Our study lays the theoretical foundation of highefficiency electricfieldinduced spin dynamics in intrinsic antiferromagnetic topological insulators. 
Wednesday, March 16, 2022 1:06PM  1:18PM 
N72.00009: Bellstate generation for spin qubits via dissipative coupling Ji Zou, Shu Zhang, Yaroslav Tserkovnyak We theoretically investigate the dynamics of two spin qubits interacting with a magnetic medium. A systematic theoretical framework for this qubitmagnet hybrid system is developed in terms of the equilibrium properties of the magnetic medium. Our particular focus is on the induced dissipative coupling between the spin qubits. In contrast to the conventional wisdom that dissipation is detrimental to quantum effects, here we show that a sizable longlifetime entanglement can be established via a dissipative environment, in the absence of any coherent coupling. Moreover, we demonstrate that maximallyentangled twoqubit states (Bell states) can be achieved in this scheme when complemented by proper postselection. In this situation, there is a dynamical phase transition separated by an exceptional point. The resultant Bell state is robust against weak random perturbations and does not require the preparation of a particular initial state. Our study may find applications in quantum information science, quantum spintronics, and for sensing of nonlocal quantum correlations. 
Wednesday, March 16, 2022 1:18PM  1:30PM 
N72.00010: Evolution of band topology with antisite defects in the Sbdoped MnBi_{4}Te_{7} ShangWei Lien Magnetic topological materials attract worldwide attention because the interplay between band topology and magnetism may lead to novel topological quantum phenomena, such as quantum anomalous Hall effect and quantized magnetoelectric effect. Here we propose a tunable magnetic and topological state in Sb doping a newly discovered intrinsic antiferromagnetic (AFM) topological insulator (TI) MnBi_{4}Te_{7}. Our firstprinciples calculation shows that the topological ground state transfer from AFM TI to ferromagnetic axion insulator in the low doping region, and then exhibit a typeI ferrimagnetic Weyl semimetal that resulted from strong antisite disorder in the high doping region. Our calculation demonstrates that the doping series provides a fruitful platform with continuously tunable magnetism and topology for investigating emergent phenomena. 
Wednesday, March 16, 2022 1:30PM  1:42PM 
N72.00011: Kagome Magnet RMn_{6}Sn_{6}: Firstprinciples study HungJu Tien, JiaXin Yin, ZiJia Cheng, TayRong Chang, Shuang Jia, M. Zahid Hasan Kagome lattice is a twodimensional honeycomb structure network with triangular corner sharing. The band structure of kagome lattice has been theoretically predicted to possess both flat bands and Dirac states in the Brillouin zone. In addition, the band degeneracy will be lifted and present a topological nontrival gap as considering timeinvariant intersite spinorbit coupling. Recently, a new kagome family RMn_{6}Sn_{6} has been found to provide a tunable magnetic configuration by replacing different rare earth elements R. For example, TbMn_{6}Sn_{6} (R=Tb) shows a ferrimagnetic state with ourofplane spin orientation. Based on firstprinciples calculations, we identify a highly orbitalselective massive Dirac state forming by Mn d_{x2y2}/d_{xy} with 35 meV large energy gap at K point, which is well consistent with our tunneling measurement [1]. Remarkably, our calculation exhibits the strong Berry curvature in this gapped Dirac state, supporting TbMn_{6}Sn_{6} may be an intrinsic Chern insulator. Besides TbMn_{6}Sn_{6}, we find an inplane spin configuration in GdMn_{6}Sn_{6}. Our firstprinciples calculations demonstrate a magnetic nodalline state resulted from the nearly gapless Dirac cone around K point in this easyplane ferrimagnet spin structure. Our calculation reveals an orbitalselective and a tunable topological gap in kagome magnet RMn_{6}Sn_{6} and provide a natural platform to investigate the interplay between topology and magnetism. 
Wednesday, March 16, 2022 1:42PM  1:54PM 
N72.00012: Unraveling peculiar magnetism and band topology in Mn_{3}Sb Gopi C Kaphle, Balaram Regmi, Ram B Ray, Durga Paudyal Magnetic, pseudogap, topological, magnetostructural, and elastic behaviors of Mn 3 Sb have been unraveled. The ferrimagnetism (FIM) is described by localized and delocalized electron magnetism resulting in different magnetic moments on Mn atoms, confirming the neutron diffraction data. The identified magnetostructural properties are due to the nonequivalent Mn atoms in its lowest symmetry structure. The electronic structure is also unique due to variable valance states of Mn atoms. The magnetic moment (4.10 μ_{B }) of nonequivalent Mn1 atom is antiparallely aligned with the magnetic moments (2.34 μ_{ B} ) of Mn2 and Mn3 atoms. The estimated Curie temperature, T C , is higher than the room temperature, which may have above the room temperature applications in spintronic devices. The band structure and density of states (DOS) show the characteristics of band topology (opening of a gap in Diraclike band features) and pseudogap, respectively, around the Fermi level. While expanding the unit cell, the tetragonal FIM ground state 
Wednesday, March 16, 2022 1:54PM  2:06PM 
N72.00013: Morphology and MagnetoTransport Properties of Submicron Grains of the Topological Antiferromagnet Mn_{3}Sn Takumi Matsuo, Tomoya Higo, Satoru Nakatsuji, Daisuke NishioHamane The topological antiferromagnet Mn_{3}Sn [0] exhibits ferromagneticlike responses such as the Anomalous Hall and Nernst Effects (AHE/ANE) due to its timereversal symmetry breaking magnetic structure [1,2]. Recently, Mn_{3}Sn thin films have been of interest due to their role in spintronics [3,4], and studies of submicron Mn_{3}Sn particles could expand the material’s use in nanotechnology. In this work, Mn_{3}Sn films with varying thickness t were fabricated by DC magnetron sputtering on Si/SiO_{2} substrates at crystallization temperature. Through atomic force microscopy (AFM) measurements, our films were seen to be amalgamations of submicron formations. When t ≦ 20 nm, individual isolated grains made up the films. Depending on t, the sizes of these grains vary from tens to hundreds of nanometers. AHE was observed in the Mn_{3}Sn grains covered by a conducting layer, suggesting that our grains possess finite Berry curvature in momentum space, which could further cement the material’s role in spintronics. 
Wednesday, March 16, 2022 2:06PM  2:18PM 
N72.00014: Colossal angular magnetoresistance in a ferrimagnetic nodalline semiconductor Mn_{3}Si_{2}Te_{6} Junho Seo, CHANDAN DE, Hyunsoo Ha, Ji Eun Lee, Sungyu Park, Joonbum Park, Yurii Skourski, Eun Sang Choi, Bongjae Kim, Gil Young Cho, Han Woong Yeom, SangWook Cheong, Jae Hoon Kim, BohmJung Yang, Kyoo Kim, Jun Sung Kim Topological magnets, where both magnetism and nontrivial band topology coexist, have emerged as promising candidates to realize novel electronic and spintronic functionalities, because their topological band degeneracy can be readily tuned by spin configurations, thus dramatically modulating electronic conduction. Here we propose a new class of topological magnets, namely, magnetic nodalline semiconductors, in which spinpolarized conduction or valence bands possess topological nodalline degeneracy. Taking a layered ferrimagnet Mn_{3}Si_{2}Te_{6} as a model system, we show that the topological band degeneracy, driven by chiral molecular orbital states, is lifted depending on the spin orientation, which leads to a metalinsulator transition in the same ferrimagnetic phase. As a result, we have observed extremely large angular magnetoresistance exceeding a trillion percent per radian, which we call colossal angular magnetoresistance. Our findings highlight that magnetic nodalline semiconductors are a promising platform for realizing extremely sensitive spin or orbitaldependent functionalities. 
Wednesday, March 16, 2022 2:18PM  2:30PM 
N72.00015: Transport and magnetic properties of the topological (Weyl) semimetal: Hexagonal  (Mn_{1α}Fe_{α})_{3}Ge (α = 0 – 0.3) Venus Rai, Shibabrata Nandi, Anne Stunault, Wolfgang Schmidt, Subhadip Jana, JianRui Soh, Joerg Persson, Thomas Brueckel In the case of Mn_{3}Ge, the anomalous Hall effect (AHE) has its origins in the topological Weyl nodes. The AHE can be controlled by tuning of the Weyl points relative to the Fermi surface, by suitable dopants of the parent phase. Therefore, we have explored the electrical transport and magnetic properties of the single crystal (Mn_{1α}Fe_{α})_{3}Ge to study the change in AHE and chiral anomaly with Fe doping. Clear signatures of the AHE and chiral anomaly were observed for samples up to α = 0.22, in the temperature regime where magnetization behaves the same as the parent sample. However, the strength of AHE and chiral anomaly decreases with an increase in Fe doping and vanishes beyond α = 0.22. To predict the origin of AHE in doped samples, the ground state magnetic structure of α = 0.22 was determined using singlecrystal (polarized and unpolarized) neutron diffraction techniques. We observed that the magnetic structure of the doped sample remains the same as that of the parent compound in the temperature regime where AHE was observed. These observations led us to two main conclusions: (i) the Weyl points are very likely to be present in the doped samples, and (ii) the characteristics of the Weyl points can be tuned significantly by suitable doping of the Weyl semimetals. 
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