Bulletin of the American Physical Society
APS March Meeting 2019
Volume 64, Number 2
Monday–Friday, March 4–8, 2019; Boston, Massachusetts
Session E04: Dirac/Weyl Semimetals  Materials Prediction IFocus

Hide Abstracts 
Sponsoring Units: DMP Chair: Arun Bansil Room: BCEC 107C 
Tuesday, March 5, 2019 8:00AM  8:12AM 
E04.00001: Weyl Points Enabled by Threedimensional Flat Band Yinong Zhou, KyungHwan Jin, Huaqing Huang, Zhengfei Wang, Feng Liu Topological flat band (FB) has attracted much interest because it exhibits a range of exotic quantum phases. Here, we discover yet another novel physical manifestation arising from threedimensional (3D) FB but absent for 2D FB. We show that in the presence of spinorbit coupling, magnetization of 3D FBs induces a transition from a 3D topological insulator (TI) into a Weyl semimetal, while for a 2D FB a transition from a 2D TI into a Chern insulator is known previously. The Weyl semimetal so formed may contain only a minimum of two Weyl points. The formation of Weyl points by symmetry breaking of highly degenerate 3D FBs is distinctively different from the conventional mechanism by symmetry breaking of a Dirac point. We demonstrate this unusual 3DFBenabled Weyl state first in a pyrochlore lattice model using tightbinding method and then in a real material Sn_{2}Nb_{2}O_{7} using firstprinciples calculations. The main features of the resulting Weyl points are analyzed with respect to symmetry, topological invariant and surface state. The Weyl fermions associated with FB may open new frontiers in the research of topological physics and materials. 
Tuesday, March 5, 2019 8:12AM  8:24AM 
E04.00002: Probing Hydrodynamic Materials from First Principles Jennifer Coulter, Prineha Narang In the hydrodynamic regime of transport, momentumconserving scattering dominates momentumrelaxing processes such as Umklapp, defect, and boundary scattering so that momentum is quasiconserved and electron flow obeys the formalism of hydrodynamics. In light of recent experimental evidence of hydrodynamic transport in PdCoO2, WP2, and PtSn4, understanding the specifics of microscopic scattering processes in these materials is of fundamental interest. In order to provide a more comprehensive perspective of experimentally observed hydrodynamic phenomena, we use firstprinciples methods including calculations of electronphonon coupling to evaluate a number of different scattering lifetimes, the electrical and thermal conductivities, and optical properties of these materials. Through our ab initio framework, we aim to to probe the microscopic properties of the recently experimentally observed hydrodynamic solids and study the interplay between topological physics and ultrafast dynamics in these materials. 
Tuesday, March 5, 2019 8:24AM  8:36AM 
E04.00003: Catalogue of Topological Electronic Materials Tiantian Zhang, Yi Jiang, Zhida Song, He Huang, Yuqing He, Zhong Fang, Hongming Weng, Chen Fang Topological electronic materials are new quantum states of matter hosting novel linear responses in the bulk and anomalous gapless states at the boundary, and are for scientific and applied reasons under intensive research in physics and in materials sciences. Here we introduce an effective, efficient and fully automated algorithm in obtaining the topological invariants for all nonmagnetic materials that are known to human, based on recently developed principles that allow for exhaustive mappings between the symmetry representation of occupied bands and the topological invariants. Equipped with this method we have scanned through a total of 39519 materials available in structural databases, and found that as many as 8056 of them are actually topological (8889 if spinorbital coupling is neglected). These are further catalogued into classes of 5005 topological semimetals, 1814 topological insulators and 1237 topological crystalline insulators, most of which are new to human knowledge. All the results are available and searchable at http://materiae.iphy.ac.cn/; and for each topological material, we have plotted the band structure as well as the local density of states, shown on the same website. 
Tuesday, March 5, 2019 8:36AM  8:48AM 
E04.00004: Topological crossings in magnetic space groups Darshan G. Joshi, Yanghao Chan, Andreas P Schnyder Nonsymmorphic symmetry is known to enforce topological crossings in crystals. Using the elementary band irreducible representations nontrivial crossings in the form of hourglass or accordian spectrum have been discovered in certain space groups. Here we extend such an analysis to a wider domain of magnetic space groups (MSGs). We show that the magnetic corepresentations (coreps), which are derived from the nonmagnetic irreducible representations, can be used to detect nonsymmorphic symmetry enforced topological crossings in MSGs. We demonstrate this with two examples, where we find magnetic Weyl points and hourglass dispersions. DFT bandstructure calculation of corresponding magnetic materials confirms our findings. Furthermore, we compute the surface states and discuss other experimental consequences of the hourglass dispersion in magnetic materials. 
Tuesday, March 5, 2019 8:48AM  9:24AM 
E04.00005: Chemical Principles of Topological Semimetals Invited Speaker: Leslie Schoop Chemical principles can be a powerful tool for predicting, understanding and synthesizing new topological materials. In this talk I will introduce these concepts. A common practice in solid state chemistry is to connect structural motifs with properties. In this sprit, I will focus on a common structural motif, a squarenet arrangement of atoms. I will explain how simple chemical rules, for example electron counting or geometrical considerations, such as atomic distances, can be used for identifying topological semimetals in such compounds. By connecting the crystal structure to the electronic properties, we can define a tolerance factor, solely based on atomic distances, which separates squarenet based nodal line semimetals from other trivial compounds. The talk is largely based on these two references [1,2]. 
Tuesday, March 5, 2019 9:24AM  9:36AM 
E04.00006: Comparative firstprinciples study of a prototypical Dirac semimetal by GGA and SCAN metaGGA energy functionals WeiChi Chiu, Bahadur Singh, Johannes Nokelainen, Chenliang Su, Hsin Lin, Bernardo Barbiellini, Arun Bansil Density functional theory is widely used to study topological properties of materials, limitations of the underlying exchangecorrelation functionals notwithstanding. In this connection, the recently constructed stronglyconstrainedandappropriatelynormed (SCAN) metaGGA exchangecorrelation functional has shown significant improvements in many classes of materials. Here we discuss SCANbased electronic properties of the prototypical Dirac semimetal Na_{3}Bi and compare our results with those based on the commonly used generalized gradient approximation (GGA). In particular, SCAN yields a spinorbit coupling driven topological phase transition from the normal insulator to Dirac semimetal state in contrast with the GGA results. SCAN produces Diracnode locations, Fermi velocities and sband shift around the Γ point that are in better accord than the GGA predictions with the corresponding experimental results. 
Tuesday, March 5, 2019 9:36AM  9:48AM 
E04.00007: A Monopole Mining Method for High Throughput Screening Weyl Semimetals Vsevolod Ivanov, Sergey Savrasov Although topological invariants have been introduced to classify the appearance of protected electronic states at surfaces of insulators, there are no corresponding indexes for Weyl semimetals whose nodal points may appear randomly in the bulk Brillouin Zone (BZ). Here we use a well–known result that every Weyl point acts as a Dirac monopole and generates integer Berry flux to search for the monopoles on rectangular BZ grids that are commonly employed in self–consistent electronic structure calculations. The method resembles data mining technology of computer science and is demonstrated on locating the Weyl points in known Weyl semimetals. It is subsequently used in high throughput screening several hundreds of compounds and predicting a dozen new materials hosting nodal Weyl points and/or lines. 
Tuesday, March 5, 2019 9:48AM  10:00AM 
E04.00008: Topological Quantum Properties of Chiral Crystals Guoqing Chang, Benjamin J. Wieder, Frank Schindler, Titus Neupert, Suyang Xu, Hsin Lin, Zahid Hasan Chiral crystals are materials whose lattice structure with a welldefined handedness due to the lack of inversion, mirror, or other rotoinversion symmetries, which represent a broad, important class of quantum materials. Yet, the topological properties of chiral crystals have still remained largely uncharacterized. Here, we show that KramersWeyl fermions are a universal topological electronic property of chiral crystals with spinorbit coupling (SOC). Unlike conventional Weyl fermions, they appear at timereversalinvariant momenta. By combining our analysis with the results of previous works, we further determine that all pointlike nodal degeneracies in nonmagnetic chiral crystals with relevant SOC carry nontrivial Chern numbers. Using this theory, we identify representative chiral materials in 33 of the 65 chiral space groups in which topological chiral fermions are relevant to lowenergy physics. Among all the materials, RhSi family exhibit the ideal topological band structures with longest Fermi arcs and nontrivial energy windows. 
Tuesday, March 5, 2019 10:00AM  10:12AM 
E04.00009: Fermi arcs in topological chiral crystals Daniel S Sanchez, Guoqing Chang, Tyler Cochran, Kaustuv Manna, Benjamin Wieder, ShinMing Huang, Ilya Belopolski, TayRong Chang, Songtian Sonia Zhang, Suyang Xu, Arun Bansil, Claudia Felser, Hsin Lin, M Zahid Hasan The telltale trademarks of a Weyl semimetal are the topologically protected Fermi arc surface states. While these surface states have been demonstrated in conventional Weyl semimetals (for instance, the TaAs family), they should also be present in the recently proposed unconventional Weyl semimetals. However, there is still a lack of candidate materials for experimental exploration. In this talk, we comment on a number of chiral crystals in space group No. 198, as platforms for expanding the list of Fermi arc materials. Notably, RhSi, CoSi, CoGe, RhGe, AlPd, AlPt, BaPtP, and BaPtAs constitute promising candidate materials. Indeed, these compounds should exhibit the longest possible Fermi arcs, spanning across the entire surface Brillouin zone. These predictions are closely tied to the maximally separated 4fold and 6fold unconventional chiral fermions that have recently been predicted in this class of compounds. We further comment on experimental progress and the current challenges in using ARPES to observe a chiral Weyl semimetal phase with Fermi arcs in these materials. 
Tuesday, March 5, 2019 10:12AM  10:24AM 
E04.00010: Pr_{2}Ir_{2}O_{7}: when Luttinger semimetal meets MelkoHertogGingras spin ice state Xuping Yao, Gang Chen In quantum materials with multiple flavors of degrees of freedom (DOF), the interplay between them leads to intriguing phenomena and allows the mutual control. Here we study band topology and engineering from the interplay between local moments and itinerant electrons in pyrochlore iridates. For metallic Pr_{2}Ir_{2}O_{7}, the Ir 5d conduction electrons interact with the Pr 4f local moments via the fd exchange. While the Ir electrons form a Luttinger semimetal, the Pr moments can be tuned into an ordered spin ice with a finite ordering wavevector, dubbed MelkoHertogGingras (MHG) state, by varying Ir and O contents. We point out that the Pr Ising order generates an internal field that reconstructs the Ir bands. Besides the broad existence of Weyl nodes, we predict that the magnetic translation of the Pr MHG state protects the Dirac band touching at certain time reversal invariant momenta for the Ir bands. We propose the magnetic fields to control the Pr magnetism and indirectly influence the Ir electrons. Our prediction can be immediately tested in ordered Pr_{2}Ir_{2}O_{7} samples. Our theory constitutes a nontrivial and realistic example for the interplay between itinerant electrons and local moments in three dimensions, and shed lights on hybrid quantum materials with multiple flavors of DOF. 
Tuesday, March 5, 2019 10:24AM  10:36AM 
E04.00011: OpticallyControlled Orbitronics on a Triangular Lattice Vo Tien Phong, Zachariah Addison, Seongjin Ahn, Hongki Min, Ritesh Agarwal, Eugene John Mele Orbital polarization of a Bloch state in a crystal can endow a band structure with nontrivial geometry and manifest itself in unique responses to applied fields. We study this for an onsite orbital multiplet on a 2D primitive triangular lattice where orbital degeneracies are lifted by propagation on a Bravais lattice. The model contains fully orbitallyderived band structure degeneracies including a linenode required by the perpendicular mirror symmetry and two types of point degeneracies protected by PT symmetry. Crucially, and in contrast to the wellstudied analogous problem on the honeycomb lattice, here point degeneracies with opposite winding numbers are generically offset in energy which enables the activation of anomalous transport responses using readilyimplemented spatiallyuniform local potentials. We demonstrate this by calculation of an anomalous charge Hall effect activated by coherently coupling to a circularly polarized optical field and an orbital Hall effect describing an orbital angular momentum current directed perpendicular to an applied in plane electric field. 
Tuesday, March 5, 2019 10:36AM  10:48AM 
E04.00012: Chiral Vortical and Gyrotropic Effects in Weyl Semimetals Zhao Huang, Pavan Hosur The chiral anomaly is the source of various interesting phenomena for chiral fermions, and especially in Weyl semimetals which contain chiral fermions as low energy excitations. For example, a magnetic field leads to a longitudinal current flow in the absence of electric fields, well known as the chiral magnetic effect. Since the Coriolis force behaves like a Lorentz force in many ways, one expects an axial current induced by rotation for chiral fermions. This is known as the chiral vortical effect. This effect has attracted a lot of attention in nuclear physics for its possible consequences for heavy ion collisions [1]. In this work, we theoretically explore the possibility of the chiral vortical effect in Weyl semimetals. In particular, we argue that naively rotating a Weyl semimetal is not the correct way to induce the chiral vortical effect. Instead, one must rotate the chiral fluid of electrons relative to the background lattice. The latter can be achieved via an electric field with a nonzero curl, and is otherwise known as the gyrotropic effect. 
Tuesday, March 5, 2019 10:48AM  11:00AM 
E04.00013: Prediction of Weyl semimetal, AFM topological insulator, nodal line semimetal, and Chern insulator phases in Bi_{2}MnSe_{4} Sugata Chowdhury, Kevin Garrity, Francesca Tavazza Three dimensional materials with strong spinorbit coupling and magnetic interactions represent an opportunity to realize a variety of rare and potentially useful topological phases. In this work, we use first principles calculations to show that the recently synthesized material Bi_{2}MnSe_{4} displays a combination of band inversion and magnetic interactions, leading to several topological phases. In bulk form, the ferromagnetic phase of Bi_{2}MnSe_{4 }is either a nodal line or Weyl semimetal, depending on the direction of the spins. When the spins are arranged in a layered antiferromagnetic configuration, the combination of time reversal plus a partial translation is a new symmetry, and the material instead becomes an antiferromagnetic topological insulator. However, the intrinsic TRS breaking at the surface of Bi_{2}MnSe_{4} removes the typical Dirac cone feature, allowing the observation of the halfinteger quantum anomalous Hall effect (AHC). Furthermore, we show that in thin film form, for some thicknesses, Bi_{2}MnSe_{4 }becomes a Chern insulator with a band gap of up to 58 meV. This combination of properties in a stoichiometric magnetic material makes Bi_{2}MnSe_{4} an excellent candidate for displaying robust topological behavior. 
Follow Us 
Engage
Become an APS Member 
My APS
Renew Membership 
Information for 
About APSThe American Physical Society (APS) is a nonprofit membership organization working to advance the knowledge of physics. 
© 2020 American Physical Society
 All rights reserved  Terms of Use
 Contact Us
Headquarters
1 Physics Ellipse, College Park, MD 207403844
(301) 2093200
Editorial Office
1 Research Road, Ridge, NY 119612701
(631) 5914000
Office of Public Affairs
529 14th St NW, Suite 1050, Washington, D.C. 200452001
(202) 6628700