Bulletin of the American Physical Society
APS March Meeting 2018
Monday–Friday, March 5–9, 2018; Los Angeles, California
Session K10: Dirac/Weyl Semimetals  MagnetismFocus

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Sponsoring Units: DMP GMAG Chair: Fazel Tafti, Universite de Sherbrooke Room: LACC 301B 
Wednesday, March 7, 2018 8:00AM  8:36AM 
K10.00001: Transport and Magnetism in Topological Semimetals Invited Speaker: Joseph Checkelsky Topological Semimetals host unusual bulk and surface electronic modes intertwined with the magnetic and crystallographic symmetries of the host crystal. Bulk electrical transport measurements have proven to be incisive probes of the emergent properties of these states. Here we focus on the role of symmetry to control such behavior in terms of Berry curvature driven Hall effects. In both rare earth and transition element containing systems these robust effects allow for a direct probe of the exotic states near the Fermi level. We discuss prospects for designing systems with further enhanced responses via symmetry considerations. 
Wednesday, March 7, 2018 8:36AM  8:48AM 
K10.00002: Unconventional magnetism and electronic transport in magnetic Weyl semimetals RAlX Jianpeng Liu , Lucile Savary , Takehito Suzuki , Joseph Checkelsky , Leon Balents We study the electronic and magnetic properties in magnetic Weyl semimetals RGeX, where R denotes rareearth elements and X=Si/Ge. First, we find that by virtue of the strong spinorbit coupling the magnetic moments of the rare earth ions are ordered in an unconventional manner, which can be further controlled by external magnetic fields. On the other hand, the conduction electrons near the Fermi surface host both type\I\ and type\II\ Weyl nodes. Such topological conduction electrons are coupled to the local magnetic moments through Kondo couplings, which allow for the control of the Weyl nodes by manipulating the magnetic moments, leading to anomalous electronic transport behavior. 
Wednesday, March 7, 2018 8:48AM  9:00AM 
K10.00003: Domain wall magnetoresistance in disordered forromagnetic Weyl semimetal Koji Kobayashi , Yuya Ominato , Kentaro Nomura We study transport properties in magnetic junction of Weyl semimetals. The Weyl semimetal is a kind of topological quantum matter and can be realized by breaking timereversal or inversion symmetry of Dirac semimetal. In the timereversal broken type, say, ferromagnetic Weyl semimetals, the Weyl nodes (and the Fermi surface surrounding them) move in accordance with the magnetization. This results in the suppression of the transport through the interface, or, domain wall of two ferromagnetic Weyl semimetals with antiparallel magnetizations. We have numerically investigated the twoterminal conductance in the Weyl semimetals with domain walls, and found that a huge magnetoresistance effect arises in any type of (i.e., Bloch, Neel, and headtohead) domain walls. We also show that the magnetoresistance is extremely robust against potential and magnetic disorders. 
Wednesday, March 7, 2018 9:00AM  9:12AM 
K10.00004: Anomalous magnetization of the chiral antiferromagnet Mn_{3}Sn Masaaki Shimozawa , Kaori Sugii , Jun Kondo , Yoshitaka Suzuki , Minoru Yamashita , Taketomo Nakamura , Shingo Katsumoto , Yasuhiro Tada , Muhammad Ikhlas , Tomoya Higo , Takahiro Tomita , Satoru Nakatsuji , Marcin Konczykowski , Yuji Matsuda , Kiyotaka Mukasa , Kohei Matsuura , Yuta Mizukami , Takasada Shibauchi Recent experiments have revealed a large anomalous Hall effect at room temperature in Mn_{3}Sn [1]. According to the first principle calculations, the large anomalous Hall effect would originate from the Berry curvature. Here, by using a scanning Hall probe microscopy, we study magnetic properties arising from the Berry curvature in Mn_{3}Sn. We demonstrate the possibility that a boundary current circulation generated from the Berry curvature provides an orbital magnetization [2], the magnitude of which is the same order as the spin magnetization due to spin canting towards the local easy axis. [1] S. Nakatsuji, N. Kiyohara, and T. Higo, Nature 527, 212–215 (2015). [2] D. Xiao, M.C. Chang, and Q. Niu, Rev. Mod. Phys. 82, 1959 (2010). 
Wednesday, March 7, 2018 9:12AM  9:24AM 
K10.00005: Anomalous Hall Effect in Topological Antiferromagnetic State in Mn_{3}Sn Kaori Sugii , Yusuke Imai , Masaaki Shimozawa , Muhammad Ikhlas , Naoki Kiyohara , Takahiro Tomita , Satoru Nakatsuji , Minoru Yamashita Anomalous Hall effect (AHE), a Hall signal occurring even in absence of external magnetic field, is one of the most attractive phenomena in fundamental science. However, the understanding of its mechanism is challenging and is largely restricted to the ferromagnetic transition metals. Here, we investigate an anomalous thermal Hall effect (ATHE), a thermal analogue of AHE, in the chiral antiferromagnet Mn_{3}Sn [1]. We find that the amplitude of ATHE scales to the anomalous Hall conductivity according to the WiedemannFranz law over a wide temperature range, demonstrating that the AHE of Mn_{3}Sn arises from a dissipationless intrinsic mechanism induced by the Berry flux. The dissipationless nature of AHE in Mn_{3}Sn is significantly stabilized by extra Mn atoms which shift the Fermi level toward possible Weyl points and act as a scattering. This result is in sharp contrast to conventional ferromagnetic metals where a doping effect converts the scatteringfree AHE into scatteringdependent one. Our findings suggest that the Berry flux in a magnetic Weyl fermion state proposed by ab initio calculations may play an important role for inducing the AHE of Mn_{3}Sn. [1] S. Nakatsuji, N. Kiyohara, and T. Higo, Nature 527, 212 (2015). 
Wednesday, March 7, 2018 9:24AM  9:36AM 
K10.00006: Anomalous Hall Effect In Topological Magnetic Materials Kaustuv Manna , Lukas Muechler , TingHui Kao , Rolf Stinshoff , Nitesh Kumar , Jurgen Kubler , Gerhard Fecher , Chandra Shekhar , Yan Sun , Claudia Felser In recent years, topological semimetals have emerged as a new frontier in the condensed matter community. With the interplay between the structural asymmetry and spinorbit interaction, and details of Berry phase, new topological states are being discovered. Though inversion symmetry breaking Weyl fermion is demonstrated in TaAs family of compounds, the timereversal breaking examples remain elusive. Here we demonstrate the formation of magnetic nodal lines in a topological magnetic Heusler compound Co_{2}MnGa. Without spinorbit coupling (SOC), we find three nodal lines due to the band crossing in majority spin channel. With SOC, nodal lines split up giving rise to the Weyl nodes, whose momentum space distributions depend on the magnetization direction. We observe giant anomalous Hall conductivity of ~ 1600 Ω^{1}cm^{1} with room temperature anomalous Hall angle ~12% in Co_{2}MnGa. Infact, by suitable manipulations of the crystal symmetries and the band structures of the materials, one can selectively tuned the anomalous Hall conductivity from 0 to values up to 1600 Ω^{1}cm^{1} in various magnetic Heusler compounds for nextgeneration topospintronics applications. 
Wednesday, March 7, 2018 9:36AM  9:48AM 
K10.00007: Ferromagnetic Quantum Phase Transition in a Dirac Semimetal George De Coster , Dietrich Belitz , Theodore Kirkpatrick We investigate the quantum ferromagnetic transition in a Dirac Semimetal (DSM) doped away from the charge neutrality point. In an ordinary Fermi liquid the coupling of the magnetization to the fermions is known to drive the transition first order [1]. In a DSM the spin dependence of the Hamiltonian requires a reanalysis of this problem. Our theory is general, and allows us to consider both the DSM case as the limit of strong spinorbit coupling, and ordinary metallic magnets with a weak spinorbit interaction. 
Wednesday, March 7, 2018 9:48AM  10:00AM 
K10.00008: The magnetic analogs of ZrSiStype materials Leslie Schoop , Andreas Topp , Fabio Orlandi , Lukas Muechler , Maia Vergniory , Pascal Manuel , Christian Ast , Bettina Lotsch ZrSiS and related materials have been widely studied because they (a) feature a 3D Dirac line node at the Fermi level and (b) 
Wednesday, March 7, 2018 10:00AM  10:12AM 
K10.00009: Antiferromagnetic Topological Semimetals in Three Dimensions Jing Wang We study threedimensional topological semimetals with magnetic ordering and strong spinorbit interaction. Such topological semimetals include Dirac semimetals (DSMs) and nodal line semimetals (NLSMs). Two distinct classes of magnetic NLSMs are proposed. The first class is bandinversion NLSM where the accidental line node is induced by band inversion and locally protected by glide mirror plane and the combined timereversal and inversion symmetries. This can be viewed as a trivial stacking of the twodimensional antiferromagnetic Dirac semimetals. The second class is essential NLSM where the nodal features are filling enforced by specific magnetic symmetry group. Similar classification also applies to magnetic DSMs. Concrete tightbinding models for magnetic NLSMs and DSMs which belong to these two different classes are also provided. 
Wednesday, March 7, 2018 10:12AM  10:24AM 
K10.00010: Theory of Large Intrinsic Spin Hall Effect in Iridate Semimetals Adarsh Patri , Kyusung Hwang , HyunWoo Lee , YongBaek Kim We theoretically investigate the mechanism to generate large intrinsic spin Hall effect (SHE) in iridates or more broadly in 5d transition metal oxides with strong spinorbit coupling. We demonstrate such a possibility by taking the example of orthorhombic perovskite iridate with nonsymmorphic lattice symmetry, SrIrO3, which is a threedimensional semimetal with nodal line spectrum. It is shown that large intrinsic SHE arises in this system via the spinBerry curvature originating from the nearly degenerate electronic spectra surrounding the nodal line. This effect exists even when the nodal line is gently gapped out, due to the persistent nearly degenerate electronic structure, suggesting a distinct robustness. The magnitude of the spin Hall conductivity (SHC) is shown to be comparable to the best known example such as doped topological insulators and the biggest in any transition metal oxides. To gain further insight, we compute the intrinsic SHC in both of the bulk and thin film systems. We find that the geometric confinement in thin films leads to significant modifications of the electronic states, leading to even bigger SHC in certain cases. We compare our findings with the recent experimental report on the discovery of large SHE in SrIrO3 thin films. 
Wednesday, March 7, 2018 10:24AM  10:36AM 
K10.00011: The interplay of nontrivial band topology and magnetism in HalfHeusler alloys (Tb/Dy)PtBi Yanglin Zhu , Jin Hu , David Graf , Zhiqiang Mao HalfHeusler compound GdPtBi is one of the few time reversal symmetry breaking Weyl semimetals induced by magnetic field and is characterized by the chiral anomaly and the anomalous Hall effect with an exceptionally large Hall angle θ_{H} (≈0.2)[13]. In order to understand how the Weyl bands interplay with magnetism in HalfHeusler alloys, we have studied magnetotransport properties of (Tb/Dy)PtBi. We observed anomalous Hall effects in both materials and find their Hall angles as well as magnetoresistance sensitively depend on their magnetic states. In TbPtBi, its θ_{H} is found to be 0.4, twice that of GdPtBi and its magnetoresistance shows signatures of chiral anomaly. However, for DyPtBi, although Dy carries magnetic moment greater than those of Gd and Tb, it does not show chiral anomaly and its θ_{H} is much smaller. There discrepancies can be attributed to the different magnetic states of these two materials. These findings suggest that the nontrivial band topology under magnetic field of halfHeusler alloys is intimately associated the magnetism generated by rare earth element. 
Wednesday, March 7, 2018 10:36AM  10:48AM 
K10.00012: Metamagnetic phase transitions in the orthorhombic antiferromagnetic topological semimetal CuMnAs Eve Emmanouilidou , Huibo Cao , Ni Ni Anisotropic magnetic materials are known to exhibit fieldinduced spinflip or spinflop phase transitions if the external field is applied along the easy axis. Recently, orthorhombic CuMnAs was proposed to be a promising candidate in antiferromagnetic spintronics. It is thus interesting to study how spins interact with external magnetic fields. Our previous study has shown that the magnetism in orthorhombic CuMnAs is very sensitive to the Cu vacancies and Cu/Mn site mixing. While Cu_{0.95}MnAs shows a single paramagnetic to commensurate antiferromagnetic phase transition at 360 K, Cu_{0.98}Mn_{0.96}As shows a paramagnetic to incommensurate antiferromagnetic phase transition at 320 K followed by an incommensurate to commensurate antiferromagnetic phase transition at 230 K. In this talk we will present our findings on the anisotropic magnetic properties for fields up to 7 T of the single crystalline orthorhombic topological semimetal Cu_{0.95}MnAs and Cu_{0.98}Mn_{0.96}As, which again are very sensitive to the stoichiometry of the material. 
Wednesday, March 7, 2018 10:48AM  11:00AM 
K10.00013: Weyl magnon in magnetic diamond lattice Daichi Kurebayashi , Koji Sato , Oleg Tretiakov , Kentaro Nomura Threedimensional topological nodal semimetals have been intensely studied. Recently, it is proposed that the bosonic analogues of the systems, Weyl magnon semimetals, can be realized in magnetic systems. In the Weyl magnon semimetals, a dispersion relation is described by the relativistic Weyl equation around band touching points, and there are flat surface bands connecting the bulk Weyl points, analogues to the fermiarc states in Weyl semimetals. Because of the relativistic nature in the dispersion, magnon transport phenomena related to the chiral anomaly are expected. However there are only few systems proposed to possesses the Weyl magnon states. In this talk, we propose a new candidate for Weyl magnon semimetals. We study the magnetic excitations in the ferromagnetic diamond lattice. As a result, we find that the Weyl magnon semimetal can be realized. We also discuss magnon transport induced by electric fields. Since magnons have been gathering attention as lowdissipation carriers in spintronics, electric manipulation of Weyl magnon might provide a new way to realize lowenergyconsumption devices. 
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