Bulletin of the American Physical Society
APS March Meeting 2020
Volume 65, Number 1
Monday–Friday, March 2–6, 2020; Denver, Colorado
Session F19: Correlated and Magnetic Topological MaterialsInvited

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Sponsoring Units: GMAG Chair: Claudia Felser, Max Planck Inst Room: 207 
Tuesday, March 3, 2020 8:00AM  8:36AM 
F19.00001: Threedimensional correlated topological semimetals Invited Speaker: Johannes Gooth The physics of topological materials is typically well described by the band theory of noninteracting fermions. In contrast, some of the most fascinating effects in condensed matter physics merely emerge from electron correlations. Here, we will present two recent examples of phases of matter, arising from the interplay of interaction and nontrivial topology: an axionic charge density wave and threedimensional quantum Hall states. Our electrical transport measurements reveal a positive longitudinal magnetoconductance in the sliding mode of the quasionedimensional CDW–Weyl semimetal (TaSe_{4})_{2}I, a signature that is linked to the presence of an axionic phason. In addition, we report the observation of integer and fractional quantum Hall plateaus in the bulk semimetal HfTe_{5}. 
Tuesday, March 3, 2020 8:36AM  9:12AM 
F19.00002: A catalogue of nonmagnetic and magnetic topological materials Invited Speaker: Nicolas Regnault The advent of Topological Quantum Chemistry (TQC) and Magnetic Topological Quantum Chemistry (MTQC) provides a straightforward approach to look at the topological properties of a material through abinitio calculations. Combined with the nonmagnetic material database from the Inorganic Crystal Structure Database and the Bilbao Magnetic Material Database, this allows for a systematic search of topological materials. In this talk, we will present the two databases of topological materials that we now provide to the community. Overall more than 37000 nonmagnetic and 470 magnetic unique materials are available with a full topological characterization. 
Tuesday, March 3, 2020 9:12AM  9:48AM 
F19.00003: Fermiarc diversity on surface terminations of the magnetic Weyl semimetal Co_{3}Sn_{2}S_{2} Invited Speaker: Nurit Avraham Weyl semimetals are gapless topological materials, breaking either spatial inversion or time reversal symmetry, that host Weyl fermions in the bulk and topological Fermi arcs states on their surface. The time reversal symmetry broken Weyl semimetals are particularly attractive since they enable to study the interplay between magnetism, electron correlations, and topology. While several inversion symmetry broken Weyl semimetals have been verified experimentally, showing unambiguous evidence for a time reversal symmetry breaking Weyl semimetal is quite challenging. We used scanning tunneling spectroscopy to study the ferromagnetic semimetal Co_{3}Sn_{2}S_{2} and verified spectroscopically its classification as a timereversal symmetrybroken Weyl semimetal [1]. In my talk I will describe how we visualize the topological “Fermi arc" states using quasiparticle interference measurements and show that the measured band structure of Co_{3}Sn_{2}S_{2} exhibits direct signature of time reversal symmetry breaking, induced by the magnetic order of the Co atoms. By investigating three distinct surface terminations of the sample we examined complementary aspects of the surface and bulk band structure. I will describe the various surface and bulk electronic properties we extracted from each of the terminations. In particular I will demonstrate that the three different terminations of Co_{3}Sn_{2}S_{2} exhibit not only distinct Fermiarc contours, but also distinct connectivity between the Weyl nodes. The observed Weyl node connectivity changes from intra Brillouin zone connectivity on the Sn termination to a cross Brillouinzones on the Co termination. This has significant implication on the magnetotransport properties of the Weyl electrons. Finally, the S termination allowed us to extract the extent of the Weyl gap by following the surface state dispersion. This provides a clear demonstration of the surface bulk correspondence in Weyl semimetals. 
Tuesday, March 3, 2020 9:48AM  10:24AM 
F19.00004: Chiral and magnetic topological semimetals Invited Speaker: Niels Schröter Chiral topological semimetals (which possess neither mirror nor inversion symmetries) are expected host numerous novel phenomena, such as multifold fermions with large topological charge, long Fermiarc surface states, unusual magnetotransport and lattice dynamics, and a quantized response to circularly polarized light. Until recently, all experimentally confirmed topological semimetals crystallized in space groups that contain mirror operations, which means that the aforementioned phenomena vanish [1]. 
Tuesday, March 3, 2020 10:24AM  11:00AM 
F19.00005: Chiral spin textures: antiskyrmions, elliptical skyrmions and Néel skyrmions Invited Speaker: Stuart Parkin Magnetic noncollinear spin textures that are chiral are of great current interest. We discuss various spin textures that range from chiral domain walls in synthetic antiferromagnetic racetracks to antiskyrmions and elliptical skyrmions in inverse tetragonal Heusler compounds to Néel skyrmions in a noncentrosymmetric hexagonal ternary compound. We compare the properties of these distinct spin textures to skyrmions and to magnetic bubbles. We show that the symmetry of the DzyaloshinskiiMoriya exchange that stabilizes many of these spin textures strongly influences the properties of the spin textures including especially their size, which in some cases, strongly depends on the thickness of the lamella in which they are observed. Using a combination of Lorentz transmission electron microscopy and magnetic force microscopy we show that for antiskyrmions, which we have observed in several inverse tetragonal Heusler compounds, the diameter of the antiskyrmion can be varied by more than an order of magnitude from <100 nm to more than 1 micron. This tunability is related to the important role of magnetic dipoledipole interactions. 
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