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 M51: Dirac and Weyl Semimetals: Materials and Modeling--Magnetic Weyl SemimetalsFocus Live
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Sponsoring Units: DMP DCMP GMAG Chair: Joseph Checkelsky, Massachusetts Institute of Technology MIT |
Wednesday, March 17, 2021 11:30AM - 12:06PM Live |
M51.00001: Spin fluctuation induced Weyl semimetal state in the paramagnetic phase of EuCd2As2 Invited Speaker: Ming Shi Weyl fermions as emergent quasiparticles can arise in Weyl semimetals (WSMs) in which the energy bands are nondegenerate, resulting from inversion or time-reversal symmetry breaking. Here, using photoemission spectroscopy, we observe that the degeneracy of Bloch bands is already lifted in the paramagnetic phase of EuCd2As2. We attribute this effect to the itinerant electrons experiencing quasi-static and quasi–long-range ferromagnetic fluctuations. Moreover, the spin-nondegenerate band structure harbors a pair of ideal Weyl nodes near the Fermi level. Hence, we show that long-range magnetic order and the spontaneous breaking of time-reversal symmetry are not essential requirements for WSM states in centrosymmetric systems and that WSM states can emerge in a wider range of condensed matter systems than previously thought. |
Wednesday, March 17, 2021 12:06PM - 12:18PM Live |
M51.00002: Topological Nodal Planes in Magnetic Space Groups Moritz Hirschmann, Kirill Alpin, Marc Wilde, Matthias Dodenhöft, Arthur Niedermayr, Andreas Bauer, Christian Pfleiderer, Andreas P Schnyder Topological semimetals and metals may contain nodal points or lines, i.e., zero- or one-dimensional crossings in the energy bands. In the present work we discuss an extension to two-dimensional nodal features. These nodal planes are enforced in systems described by certain nonsymmorphic space groups. We give criteria to predict nodal planes and consider in the process paramagnetic as well as magnetic space groups. Based on an analysis of symmetry eigenvalues we identify space groups with a necessarily non-zero Chern number associated to the nodal planes. The arguments are supported by minimal models and explicit calculation of the topological invariants. We have identified a number of materials with topological nodal planes, among them MnSi in its ferromagnetic phase. |
Wednesday, March 17, 2021 12:18PM - 12:30PM Live |
M51.00003: Tunable Berry Curvature Effects Through Volume-wise Magnetic Competition in a Topological Kagome Magnet Co3Sn2S2 Zurab Guguchia, Joel Verezhak, Dariusz Gawryluk, Stepan Tsirkin, Jiaxin Yin, Ilya Belopolski, Huibin Zhou, Gediminas Simutis, Songtian Zhang, Tyler Cochran, Guoqing Chang, Ekaterina Pomjakushina, Lukas Keller, Zuzanna Skrzeczkowska, Qi Wang, Hechang Lei, Rustem Khasanov, Alex Amato, Shuang Jia, Titus Neupert, Hubertus Luetkens, Zahid Hasan Magnetic topological phases of quantum matter are an emerging frontier in physics and material science. Along these lines, several |
Wednesday, March 17, 2021 12:30PM - 12:42PM Live |
M51.00004: Understanding chemical bonding in adatom configurations on the surface of the magnetic Weyl semi-metal Co3Sn2S2 with machine learning, 3D scanning tunneling spectroscopy, and first-principles calculations Kevin Roccapriore, Qiang Zou, Rui Xue, Maxim Ziatdinov, Mingming Fu, David George Mandrus, Mina Yoon, Bobby G Sumpter, Zheng Gai, Sergei Kalinin The cleaved surface of the magnetic Weyl semi-metal Co3Sn2S2 offers an ideal testing ground for understanding the chemical bonding of various adatom configurations that remain after cleavage. Changes in local electronic tunneling spectra can reveal different chemical bonding states of the adatoms, however deciphering these sometimes, subtle, changes are not straightforward. In fact, the elemental composition of the adatoms themselves has recently been under debate by several groups1,2. Here we develop a machine learning workflow that combines supervised learning in the spatial domain and unsupervised learning in the energy domain that, with direct comparison to first-principles calculations performed in-tandem, allows an enhanced understanding of the elemental composition and chemical bonding nature of the adatoms and their configurations. Our findings indicate that adatoms belonging to the same structural configuration differ in electronic structure, implying a difference in chemical bonding and possibly elemental composition, paving the way towards a more complete understanding the surface of this unique material. |
Wednesday, March 17, 2021 12:42PM - 12:54PM Live |
M51.00005: The magnetic order, tunable spin-canting, and band structure of a candidate Weyl semi-metal Keith Taddei, Duminda Sanjeewa, LI YIN, Jie Xing, Clarina Dela Cruz, Athena S. Sefat, David Parker Weyl semi-metals are novel materials which give experimental reality to exotic chiral quasi-particles originally predicted by relativistic wave equations, and in so doing provide properties desirable for device applications. However, as an unfortunate result of nature’s seeming preference for inversion symmetry breaking Weyl materials, the desired physics is often ostensibly obscured by myriad Weyl points which give rise to higher order interactions muddying clear signatures of the Weyl physics. One route to avoid this downfall is to find materials whose Weyl nodes are formed by time-reversal symmetry breaking which theoretically allows for the minimal number of Weyl points. Thus, there is a vibrant ongoing search for such ideal magnetic Weyl semi-metals with only a single split Dirac point and thus set of Weyl points. In this talk we will discuss the study of one such candidate material, elucidate its magnetic structure, provide a possible mechanism to optimize that structure for the Weyl physics and reveal how the magnetic symmetry tunes the electronic band structure. |
Wednesday, March 17, 2021 12:54PM - 1:06PM Live |
M51.00006: The effects of strain on the topology of EuCd2As2 Adrian Valadkhani, Young-Joon Song, Roser Valenti EuCd2As2 is well known for its Dirac point (DP) close to the Fermi surface. Consequently, there has been a lot of research regarding the splitting of this DP into a single pair of Weyl points (WP) mostly in the antiferromagnetic (AFM) order. Recently, there has been evidence for possible paramagnetic states with ferromagnetic (FM) spin fluctuations. Furthermore, the effects of strain on this structure remained open. Using ab-initio DFT calculations, we show the effects of strain on the AFM and FM ordered EuCd2As2. The non-strained structure shows a DP close to the Fermi surface protected by C3 symmetry. Applying strain to this compound while preserving this symmetry, allows for shifting the DP along the kz axis. By the analysis with a low-energy effective Hamiltonian, we calculate the topological properties as a function of strain. |
Wednesday, March 17, 2021 1:06PM - 1:18PM Live |
M51.00007: Large Anamolous Hall Effect in New Weyl Semimetal Kagome System: Fe3Sn Madhav Ghimire, Bishnu Belbase, Bishnu Karki, Linda Ye, Jhih-Shih You, Jorge I. Facio, Joseph Checkelsky, Manuel Richter, Jeroen Van den Brink Weyl semimetals (WSM) are recently discovered novel topological matters present in the crystals which break either time reversal symmetry or inversion symmetry or both. WSM possess crossing of the non degenerate valence and conduction band forming a Weyl node which is robust to any type of local perturbations. Here, by means of density functional theory calculations, we have investigated the electronic, magnetic and topological properties of layered kagome metal Fe3Sn. The magnetic ground state is ferromagnetic with an in-plane easy axis. Furthermore, Fe3Sn is identified as a new WSM with large value of anomalous Hall conductivity (AHC) close to the Fermi level. We will discuss in detail how the large AHC arises in new WSM Fe3Sn. |
Wednesday, March 17, 2021 1:18PM - 1:30PM Live |
M51.00008: Observation of Weyl fermions in a magnetic non-centrosymmetric crystal Daniel Sanchez, Guoqing Chang, Ilya Belopolski, Hong Lu, Jiaxin Yin, Nasser Alidoust, Xitong Xu, Tyler Cochran, Xiao Zhang, Yi Bian, Songtian Zhang, Yi-Yuan Liu, Jie Ma, Guang Bian, Hsin Lin, Suyang Xu, Shuang Jia, Zahid Hasan Here we report on the topological electronic properties in the non-centrosymmetric spin-orbit magnet PrAlGe by combining spectroscopy and transport measurements. By photoemission spectroscopy below the Curie temperature, we observe topological Fermi arcs that correspond to projected topological charges of ±1 in the surface Brillouin zone. In the bulk, we observe the linear energy-dispersion of the Weyl fermions. We further observe a large anomalous Hall response in our magneto-transport measurements, which is understood to arise from diverging bulk Berry curvature fields associated with the Weyl band structure. These results establish a novel Weyl semimetal phase in magnetic non-centrosymmetric PrAlGe. |
Wednesday, March 17, 2021 1:30PM - 1:42PM Live |
M51.00009: Defects in magnetic Weyl semimetal Co3Sn2S2 Zheng Gai, Qiang Zou, Mingming Fu, Mina Yoon, Rui Xue, Jiaqiang Yan, David George Mandrus Co3Sn2S2 is a magnetic Weyl semimetal with kagome-lattice. In such samples, the existence of bulk Weyl nodes, which are formed under broken inversion or time-reversal symmetry, creates nontrivial topological properties like robust Giant anomalous hall effect. The surface–bulk correspondence ensures the bulk bands related topological “Fermi arc” surface bands dispersion. In this presentation, we use low temperature high magnetic field scanning tunneling microscope, spin polarized STM, and quasiparticle interference (QPI) to study the influence of local defects to the Weyl nodes movement, including magnetic and nonmagnetic vacancies and adatoms. S, Co and Sn vacancies and adatoms are identified, their behavior under magnetic field are studied. The interplay among topology, defects and magnetism are discussed for the understanding of the involved quantum phenomena. |
Wednesday, March 17, 2021 1:42PM - 2:18PM Live |
M51.00010: Transport and Magnetism in Topological Materials Invited Speaker: Joseph Checkelsky Magnetism has proved to be a powerful tool for drawing out the exotic behavior of a variety of topological material systems. This includes both the manipulation of the underlying electronic ground state and the ability to produce unusual transport responses rooted in the topological aspects of the system. Here we describe our recent efforts to realize quantum materials in which this interplay manifests itself and discuss concepts of quantum material design that may allow for further exotica to be realized. |
Wednesday, March 17, 2021 2:18PM - 2:30PM Live |
M51.00011: Exploring spin-canting in the Dirac semimetal, Ca1-xNaxMnBi2, with neutron diffraction measurements. Aashish Sapkota, Igor Zaliznyak, John Tranquada, Cedomir Petrovic, Zhijun Xu, Guangyong Xu, Yangmu Li Recent optical and magnetic torque measurements of Ca1-xNaxMnBi2 suggested that the observed anomalous behavior in their dc resistivity at temperatures below the antiferromagnetic transition is consistent with the canting of the Manganese ordered moments [1]. Spin canting in the 112 families of Dirac semimetals is interesting because it can lead to the type-II Weyl state as a consequence of time-reversal symmetry breaking. However, previously reported canting driven Weyl states in other members, such as YbMnBi2 [1], are controversial and refuted by neutron diffraction measurements. To understand whether the spin-canting is behind the anomalous resistivity bump, we performed neutron diffraction measurements on two members of Ca1-xNaxMnBi2, x = 0 and 0.05. I will discuss the observed superstructure peaks, which appear consistent with the resistivity bump, in the framework of the spin canting. The result is important because it suggests Ca1-xNaxMnBi2 as a rare member of 112 Dirac semimetals with the possibility of type-II Weyl state. [1] R. Yang et. al PRL 124,137201 (2020). |
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