Bulletin of the American Physical Society
APS March Meeting 2020
Volume 65, Number 1
Monday–Friday, March 2–6, 2020; Denver, Colorado
Session L54: Computational Studies of Topological Materials 
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Sponsoring Units: DCMP Room: Mile High Ballroom 2A 
Wednesday, March 4, 2020 8:00AM  8:12AM 
L54.00001: Timereversalinvariant Weyl semimetals indicated by symmetry indictors and invariants Yuting Qian, Jiacheng Gao, Zhida Song, SiMin Nie, Zhijun Wang, Hongming Weng, Zhong Fang For the timereversal(TR)breaking centrosymmetric systems, an odd number of all the even/odd parity occupied bands, at eight inversionsymmetryinvariant (ISI) momenta, indicates the appearance of Weyl points in the systems. Here, based on the the firstprinciples calculations and symmetry analysis, we demonstrate that, for the TRpreversing noncentrosymmetric systems with S4 symmetry, the Weyl semimetal phase can be characterised by the nonequality between an invariant $\eta$ and an S4 indicator $z_2$. By applying it, we find that some candicates can be ideal Weyl semimetals in a noncentrosymmetric space group with S4 symmetry. Our firstprinciples calculations show that four pairs of Weyl points are located in the kx,y = 0 planes, being right at the charge neutrality level. An effective model has been built and captures the nontrivial topology in these materials. Our strategy to find the Weyl points by using symmetry indicators and invariants opens a new route to search for Weyl semimetals in TRinvariant systems. 
Wednesday, March 4, 2020 8:12AM  8:24AM 
L54.00002: Topological crystalline insulator: from symmetry indicators to material discovery TayRong Chang, XIAOTING ZHOU, ChuangHan Hsu, Vitor Manuel Pereira, Arun Bansil, Suyang Xu, Hsin Lin, Liang Fu Topological crystalline insulators (TCIs) are insulating electronic phases of matter in which the nontrivial topology is driven by crystalline symmetries. Recent theoretical advances have proposed new rotationalsymmetryprotected TCI states that are expected to show unique topologically protected boundary modes. The surface normal to the rotational axis in these TCIs features ''unpinned'' Dirac surface states whose Dirac points are located at generic k points. Also, due to the ''higherorder'' bulkboundary correspondence, such a 3D TCI supports 1D helical edge states. However, to date, rotationalsymmetryprotected TCIs have remained elusive in real materials. We systematically examine the topological properties of the TCI states in Ca_{2}As. On both the top and side surfaces, we show the presence of topological surface states protected independently by rotational and mirror symmetries [1]. We also discuss the van der Waals material αBi_{4}Br_{4} and the pristine bulk bismuth and show that these materials harbor TCI states protected purely by rotation symmetry [2,3], even though these materials have been long thought to be topologically trivial. 
Wednesday, March 4, 2020 8:24AM  8:36AM 
L54.00003: Emergent dual topology in the threedimensional KaneMele Pt_{2}HgSe_{3} Antimo Marrazzo, Nicola Marzari, Marco Gibertini Recently, the very first largegap KaneMele quantum spin Hall insulator was predicted to be monolayer jacutingaite (Pt_{2}HgSe_{3}), a naturallyoccurring exfoliable mineral. The stacking of quantum spin Hall monolayers typically leads to a (0;001) weak topological phase, which does not protect the existence of surface states on the (001) surface. Unexpectedly, recent ARPES experiments revealed the presence of surface states dispersing over large areas of the 001surface Brillouin zone. Such 001surface states have been shown to be topologically protected by a nonzero mirror Chern number, associated with a nodal line gapped by spinorbit interactions. Here, we extend the twodimensional KaneMele model to bulk jacutingaite and unveil the microscopic origin of the gapped nodal line and the emerging crystalline topological order. By using maximallylocalized Wannier functions, we identify a large nontrivial second nearestlayer hopping term that breaks the standard paradigm of weak topological insulators. Complemented by this term, the predictions of the KaneMele model are in remarkable agreement with recent experiments and firstprinciples simulations, providing an appealing conceptual framework also relevant for other layered materials made of stacked honeycomb lattices. 
Wednesday, March 4, 2020 8:36AM  8:48AM 
L54.00004: Doping induced topological phase transition in Bi: The role of quantum electronic stress KyungHwan Jin, Han Woong Yeom, Feng Liu Charge doping is an essential means to tailor materials’ properties. However, besides moving the Fermi level, charge doping is generally not expected to induce topological phase transition (TPT). Surprisingly, using firstprinciples calculations, here we demonstrate an electron doping induced TPT in bulk Bi from a higherorder topological insulator (HOTI) to a TI. The underlying mechanism is revealed to be driven by an electron doping induced quantum electronic stress (QES), which in turn induces a highly anisotropic lattice expansion to close/reopen the small energy gap in Bi band structure. Our finding significantly resolves an outstanding controversy concerning the topological characterization of bulk Bi among existing experiments and theories, and explains the physical origin of the topologic order in Bi (111) thin films. It sheds new lights to fundamental understanding of topological properties of small band gap materials in relation to doping and QES. 
Wednesday, March 4, 2020 8:48AM  9:00AM 
L54.00005: Possibility of topological properties in 2D cadmium chalcogenide (CdX, X = S, Se, and Te) buckled honeycomb monolayer on substitutional doping Sutapa Chattopadhyay, Anjali Kshirsagar Twodimensional honeycomb monolayers doped with tin atoms are designed from (111) surface of bulk zinc blende structures of cadmium chalcogenides using first principles density functional theory based calculations. On relaxation the buckled honeycomb monolayer shows signature of band inversion between Sn and Cd orbital at the zone center (Γ point) deep in the valence band and high above in the conduction band. The band inversion, due to hybridization, stays even after inclusion of spinorbit coupling. The systems were chosen with an intention to exploit the possibility of dd band inversion. CdSnS has ss band inversion but CdSnSe and CdSnTe monolayers do show band inversion involving d states. The calculated phonon spectra confirmed the stability of all the systems studied. The details of the electronic structure bring out the importance of sd band inversion. We also report the topological invariants and analysis of edge state properties and band structure of these materials in ribbon geometry. Such systems can be useful for technological application in the Spintronic domain. 
Wednesday, March 4, 2020 9:00AM  9:12AM 
L54.00006: The electronic and topological properties of plumbene by firstprinciples calculations Yue Li, Zhongqin Yang Combining tightbinding (TB) models with firstprinciples calculations, we investigate the electronic and topological properties of plumbene. “Constructive” coupling effects of topological states are found in the plumbene, causing the system being a normal insulator, opposite to topologically nontrivial states formed in the other group IVA monolayers. Based on this mechanism, several schemes are raised to produce a globally topological state in the plumbene. Interestingly, after the edge modification in the nanoribbon structure, the plumbene can own lowdissipation tunable edge states with good conduction performance despite the topologically trivial behavior. 
Wednesday, March 4, 2020 9:12AM  9:24AM 
L54.00007: Topological States in βPbO_{2}? Sharad Mahatara, Boris Kiefer The electronic properties of βPbO_{2}, have been controversial for over a century. Experiments find metallic behavior, attributed to its defect structure, to indirect semiconducting for stochiometric samples, with a gap of 0.61 eV. Theory leads to similar ambiguities, and predicts this phase to be metallic (PBE, HSE06) or the opening of too small a bandgap (HSE06). An area where this inconsistency is significant, is when a material property depends on the electronic structure in the vicinity of the Fermi energy, such as topological states. In our work, we use a selfconsistent DFT+U approach and find stochiometric βPbO_{2} to be an indirect semiconductor with a band gap of ~0.8 eV, similar to experiment. The larger bandgap requires strains of ~4% to drive βPbO_{2} into a nodal line semimetallic state, which is not protected under the application of spinorbitcoupling. Moreover, our surface computations do not show any topologically protected states near the Fermi energy. Therefore, our results show that in contrast to previous computations βPbO_{2} is a topologically trivial material, consistent with experiment. Differences to previous work can be attributed to our more accurate description of the optical properties of bulk βPbO_{2}. 
Wednesday, March 4, 2020 9:24AM  9:36AM 
L54.00008: ModeSelective Spontaneous Oscillation of Bandgap in Dirac Wedge Semimetals Zhigang Song

Wednesday, March 4, 2020 9:36AM  9:48AM 
L54.00009: Application of Convolutional Neural Network to Quantum Percolation in Topological Insulators Tomi Ohtsuki, Tomohiro Mano Quantum material phases such as Anderson insulator, diffusive metal, Weyl/Dirac semimetal as well as topological insulators show specific wave functions both in real and Fourier spaces. These features are well captured by convolutional neural networks, and the phase diagrams have been obtained, where standard methods are not applicable. One of these examples are the cases of random lattices such as quantum percolation. Here we study the topological insulators with random vacancies, namely the quantum percolation in topological insulators, by analyzing the wave functions via convolutional neural network. The vacancies in topological insulators are especially interesting since peculiar bound states are formed around the vacancies. We show that only a few percent of vacancies derives topological phase transition. The results are confirmed by independent calculations of localization length, density of states, and wave packet dynamics. 
Wednesday, March 4, 2020 9:48AM  10:00AM 
L54.00010: Predicting Topological Properties of Quantum Materials via Statistical Methods Thomas Mertz, Karim Zantout, Roser Valenti We discuss the topological phases of correlated and noncorrelated (insulating) quantum materials using a statistical method that explores the entire phase space. 
Wednesday, March 4, 2020 10:00AM  10:12AM 
L54.00011: Strongcoupling superconductivity and pseudogap in topological flat bands:
a quantum Monte Carlo study Johannes Hofmann, Erez Berg, Debanjan Chowdhury We study a twodimensional model of an isolated narrow topological band at partial filling with local attractive interactions. Exact quantum Monte Carlo calculations show that the ground state is a superconductor with a critical temperature that scales linearly with the interaction strength. We also find a broad pseudogap regime at temperatures above the superconducting phase that exhibits strong pairing fluctuations and a tendency towards electronic phase separation. We discuss the possible relevance of superconductivity in this unusual regime to the Physics of flat band Moiré materials, and as a route to designing higher temperature superconductors. 
Wednesday, March 4, 2020 10:12AM  10:24AM 
L54.00012: Role of van der Waals interactions in topological insulators: bulk, surface and interfaces Karunya Shailesh Shirali, William A Shelton, Ilya Vekhter It is wellknown that van der Waals interactions (vdW) play an important role on structural properties of the prototypical 3D topological insulators Bi_{2}Se_{3} and Bi_{2}Te_{3}. However, systematic investigations of different implementations of vdW interactions using density functional theory are lacking. We have performed a comprehensive comparison using both semiempirical (DFT+D2, DFT+D3, TkatchenkoScheffler) and first principles (LangrethLundqvist DF, SCANrVV10) vdW methods in bulk and surface calculations for these materials, treating structural and electronic properties on equal footing. We find that semiempirical methods, especially D2 produce structural parameters, electronic dispersion, and the Dirac velocity of the surface state close to the experimental values, while other methods exhibit serious problems when applied to Bi_{2}Se_{3} and Bi_{2}Te_{3}. We attribute these differences to the importance of the long range r^{6} tail of the vdW interaction, and we discuss its relevance for the properties of topological interfaces. 
Wednesday, March 4, 2020 10:24AM  10:36AM 
L54.00013: Topological Phases in Hydrogenated Group 13 Monolayers Ranjan Barik, Ritesh Kumar, Abhishek Singh


L54.00014: Robust descriptor for highthroughput discovery of alloyed topological insulators based on artificial intelligence Guohua Cao, Runhai Ouyang, Luca Ghiringhelli, Matthias Scheffler, Huijun Liu, Christian Carbogno, Zhenyu Zhang Significant advances have been made in predicting new topological materials using highthroughput empirical descriptors or symmetrybased indicators. To date, these approaches have been applied to materials in existing databases, and are severely limited to systems with welldefined symmetries, leaving a much larger materials space unexplored. Using tetradymites as a prototypical class of examples, we uncover a novel twodimensional descriptor by applying an artificial intelligence (AI) based approach for fast and reliable identification of the topological characters of a drastically expanded range of materials, without prior determination of their specific symmetries and detailed band structures. By leveraging this descriptor that contains only the atomic number and electronegativity of the constituent species, we have readily scanned over four million alloys in the tetradymite family. Strikingly, nearly two million new topological insulators are identified, revealing a much larger territory of the topological materials world. The present work also attests the increasingly important role of such AIbased approaches in modern materials discovery. 
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