Bulletin of the American Physical Society
APS March Meeting 2021
Volume 66, Number 1
Monday–Friday, March 15–19, 2021; Virtual; Time Zone: Central Daylight Time, USA
Session J38: Magnetism Quantum Theory and Computation StudiesFocus Live

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Sponsoring Units: GMAG DMP FIAP Chair: Hua Chen, Colorado State University 
Tuesday, March 16, 2021 3:00PM  3:36PM Live 
J38.00001: Robust edge states in magnetictexture based metamaterials Invited Speaker: Peng Yan Topological phases in magnetic materials are of great current interest in spintronics because of their fundamental significance and practical utility for robust information processing. A particularly interesting system is magnetictexturebased metamaterials, since they can offer flexible controllability that can benefit from modern spintronic techniques. The collective motion of magnetic texture or soliton is described by Thiele's equation, which results in a wavelike equation in the artificial crystal, and the equation differs from the wave equations of its electronic, photonic, and acoustic counterparts in the following respects: (i) The nonvanishing topological charge induces a gyration term that is analogous to an effective magnetic field acting on a quasiparticle, thus breaking timereversal symmetry. (ii) The inertial effect is taken into account by a mass term. A nonNewtonian gyration term is included to capture the highfrequency behavior of the magnetic texture and to determine the interaction parameters with high accuracy. (iii) The particleparticle coupling is strongly anisotropic. 
Tuesday, March 16, 2021 3:36PM  3:48PM Live 
J38.00002: Fingerprints of Universal SpinStiffness Jump in TwoDimensional Ferromagnets Roberto Troncoso Motivated by recent progress on synthesizing twodimensional magnetic van der Waals systems, I will talk about a proposal for detecting the topological BerezinskiiKosterlitzThouless (BKT) phase transition in spintransport experiments. Here we demonstrate that the spatial correlations of injected spincurrents into a pair of metallic leads can be used to measure the predicted universal jump of 2/π in the ferromagnet spinstiffness. Our setup provides a simple route to measuring this (up to now elusive) topological phase transition in twodimensional magnetic systems. It is hoped that this will encourage experimental efforts to investigate critical phenomena beyond the standard GinzburgLandau paradigm in lowdimensional magnetic systems with no local order parameter. 
Tuesday, March 16, 2021 3:48PM  4:00PM Live 
J38.00003: Van der Waals interactions in molecules and solids from quantum Monte Carlo Olle Heinonen, Hyeondeok Shin, Anouar Benali Many materials of intense current interest are layered materials or molecules in which dispersive van der Waals interactions play a central role, for example CrI_{3}, WTe_{2}, phosphorene, graphene and and its allotropes. In these materials, the electronic properties depend sensitively on the interlayer separation and stacking. While commonly used density functional theory (DFT) methods work well for covalent bonding, they have difficulties capturing all aspects of van der Waalsbonded systems. The L7 molecular test set was designed specifically to highlight dispersive interactions [1]. We will compare results on L7 from highly accurate diffusion Monte Carlo simulations from those of DFT methods, including bonding energy but also charge densities, and also discuss these results in the context of layered van der Waalsbonded materials. 
Tuesday, March 16, 2021 4:00PM  4:12PM Live 
J38.00004: Unusual Friedel and RKKY responses in 3D quadratic bandtouching Luttinger semimetals Louis J. Godbout, Serguei Tchoumakov, William WitczakKrempa We study the response of Luttinger semimetals, such as alphaSn, HgSe, HgTe, YPtBi and Pr_{2}Ir_{2}O_{7}, to charge and magnetic impurities. In these materials the strong spinorbit coupling and quadratic bandtouching lead to unusual Friedel and RudermanKittelKasuyaYoshida (RKKY) oscillations, as well as an asymmetry in the response upon electron or hole doping. We also examine the magnetic Pauli and Landau susceptibilities, which differ from those of regular metals. These results motivate the study of Kondo physics in Luttinger semimetals, where novel quantum phases can arise due to spinorbit coupling. 
Tuesday, March 16, 2021 4:12PM  4:24PM Live 
J38.00005: Analogues of light and gravity in the collective excitations of quantum magnets Leilee Chojnacki, Rico Pohle, Nicholas Shannon Condensed matter systems offer parallels to some of the most important phenomena in highenergy physics, exemplified by the AndersonHiggs transition in superconductors and magnetic monopoles in spin ice. Here we ask whether similar parallels exist between the fundamental force carrying particles of electromagnetism and gravity and the collective excitations of quantum magnets. 
Tuesday, March 16, 2021 4:24PM  4:36PM Live 
J38.00006: Detection of KardarParisiZhang Hydrodynamics in a quantum Heisenberg spinhalf chain Nicholas Sherman, Allen Scheie, Maxime Dupont, Stephen E Nagler, Matthew Brandon Stone, Garrett E Granroth, Joel Ellis Moore, David A Tennant Classical hydrodynamics is a remarkably versatile description of the coarsegrained behavior of manyparticle systems once local equilibrium has been established. The form of the hydrodynamical equations is determined by the conserved quantities present in a system. Generically, there is a small number of conserved quantities, which give rise to diffusive transport properties. However, in integrable systems with an extensive number of conserved quantities, more exotic transport properties are possible. In particular, recent work suggests the spinhalf Heisenberg chain exhibits KardarParisiZhang (KPZ) dynamics at infinite temperature. In this work, we study the dynamical structure factor using a tensor network approach, and show signatures of KPZ survive at finite temperatures. Moreover, we find excellent agreement with neutron scattering experiments on the compound KCuF3, suggesting KPZ physics is present. 
Tuesday, March 16, 2021 4:36PM  4:48PM Live 
J38.00007: First Principles Studies of Feintercalated $\mathrm{NbS_2}$ Sophie Weber, Jeffrey Neaton Recent experiments on $\mathrm{Fe_{1/3}NbS_2}$, a bulk antiferromagnet (AFM) with a N{e}el temperature of 42K, have shown that an applied current can reversibly switch the magnetic order, which is read out in the resistivity*. The resistivity changes are thought to be caused by a redistribution of magnetic domains**. To shed light on these findings, we examine the magnetic properties and transport of $\mathrm{Fe_{1/3}NbS_2}$ using density functional theory calculations. We find two neardegenerate magnetic states corresponding to an inplane stripe and zigzag ordering, in agreement with neutron measurements. We show that the inplane conductivity for both magnetic orders is anisotropic, consistent with domain repopulation being the basis for the electrical switching. However, the anisotropy with zigzag AFM order is reduced with respect to that of stripe order due to the strong nearestneighbor exchange. 
Tuesday, March 16, 2021 4:48PM  5:00PM Live 
J38.00008: Domain wall displacement in multisegmented nanowires Voicu Dolocan The precise manipulation of domain walls in nanowires is an essential condition for the realization of memory devices based on domain walls (DWs) displacement. To achieve the controlled movement of the DWs between welldefined positions, a pinning mechanism is needed. An initial approach is to pin the DWs at artificial constrictions in the nanowire and train of such DWs can be displaced regularly. Another approach is to modify locally the material parameters by modulating for example the anisotropy along the wire. In this presentation, we show that using a multisegmented nanowire, the precise manipulation of transverse DWs can be achieved depending on the segments length and materials parameters. The competition between the variation of anisotropy and demagnetizing energy is crucial to obtain the controlled motion. Furthermore, in some cases, the DW displacement with polarity changing can be obtained even with thermal stability just by manipulating the current pulse shape. This paves the way for practical applications with bit encoding in the DWs polarity. 
Tuesday, March 16, 2021 5:00PM  5:12PM Not Participating 
J38.00009: A Superatomic Dimer with Massive Spin Magnetic and Internal Electric Dipole Moments Dinesh Bista, Turbasu Sengupta, Arthur C Reber, Shiv Narain Khanna Ligated metalchalcogenide clusters have attracted considerable interest due to the recent developments in the synthesis process and their assembly into solids. In this work, the electronic and magnetic properties of the Fe_{6}S_{8} cluster attached with ligands and the fused superatomic dimer are investigated using the firstprinciples density functional theory. It is shown that the redox properties of the Fe_{6}S_{8} cluster can be effectively controlled by altering the nature of the attached ligands. Donor ligands such as phosphines reduce the ionization energy of the Fe_{6}S_{8} cluster, whereas the acceptor ligands such as CO increase the electron affinity. Such variation in the redox properties of the Fe_{6}S_{8} cluster is the result of the ligandinduced shift in the cluster’s electronic levels, so the occupation number remains mostly unaffected, leading to only marginal variation in the spin magnetic moment of the cluster. The fusion of two Fe_{6}S_{8} clusters decorated by unbalanced ligands forms a superatomic dimer, which exhibits rare features: a massive dipole moment and a large spin magnetic moment. The resulting superatomic dimer offers an exciting motif for spintronicsrelated applications. 
Tuesday, March 16, 2021 5:12PM  5:24PM Live 
J38.00010: Quantum spin Hall effect in twodimensional metals without spinorbit coupling Richard Klemm, Aiying Zhao, Qiang Gu, Thomas Bullard, Timothy J. Haugan The quantum spin Hall effect (QSHE) has been observed in topological insulators using spinorbit coupling (SOC) as the probe, but it has not yet been observed in a metal. We propose an experiment to measure the QSHE of an electron or hole in a twodimensional (2D) metal without SOC. Through the inner radius of a 2D metallic Corbino disk lies a long solenoid, and a radial charge current is applied between the inner and outer disk radii, thereby inducing a uniform fixed potential differentce across those radii. By combining changes in the flux in the solenoid and in the potential difference, spontaneous quantized azimuthal currents that can depend upon the particle's spin are generated. 
Tuesday, March 16, 2021 5:24PM  5:36PM Live 
J38.00011: Heterogeneous Chaos in Fewbody Dynamics Negin Moharrami Allafi, Vadim Oganesyan We study the timeevolution of classical spindimer system and nature of the transition from nonchaotic into the chaotic region of phase space. We apply complementary numerical diagnostics including lyapunov spectra and boxcounting of trajectories to quantify the degree of chaoticity and compare with other better known models such as standard maps. 
Tuesday, March 16, 2021 5:36PM  5:48PM Live 
J38.00012: Magnetic oxygen in transition metal oxides: A case study of Ba2CoO4 Lin Hou Transition metal oxides (TMOs) exhibit exotic magnetic properties, often difficult to understand in conventional wisdom. Magnetic insulator Ba2CoO4 has mystified the community, because the CoO4 tetrahedron appears to be completely isolated with the nearest Co atoms far apart (~5 Å), making it difficult to account for longrange magnetic ordering seen experimentally using only Co. By firstprinciples calculations in bulk Ba2CoO4, we illustrate for the first time that the magnetic moment on oxygen atoms are the origin of the unexpected longrange magnetic ordering and low magnetic dimensionality. We find that the magnetic moment is not only localized on Co atoms, as assumed in all conventional data analysis, but also distributed on its tetrahedrallycoordinated O atoms, making CoO4 the magnetic building block instead of Co alone. Having oxygen contribute to the magnetic moment may be identified as a universal property of magnetic TMOs, which will require a fresh look at conventional models of magnetism in TMOs. 
Tuesday, March 16, 2021 5:48PM  6:00PM Live 
J38.00013: Exact solution of the linearized Boltzmann equation for the lowtemperature resistivity in metallic ferromagnets. James Amarel, Dietrich Belitz, Theodore Kirkpatrick In clean metallic ferromagnets at asymptotically low temperature, the magnonexchange contribution to the electrical resistivity is exponentially suppressed due to the exchange gap [1]. The powerlaw prefactor of the exponential term is difficult to determine because the gap provides an energy scale in addition to the temperature. To solve this problem, we developed a technique for obtaining exact solutions to the linearized Boltzmann equation in the lowtemperature limit. Our method dispenses with the various uncontrolled approximations that have been used in all previous solutions of the integral equations for the transport coefficients. We present a rigorous proof of Bloch's T^5 law due to electronphonon scattering [2] and give the corresponding result for scattering by magnons [3]; the prefactor of the exponential is asymptotically independent of the temperature. 
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