Bulletin of the American Physical Society
APS March Meeting 2018
Monday–Friday, March 5–9, 2018; Los Angeles, California
Session L12: Computational Materials Design - New Magnetic, Topological, and High-Tc Superconductor Materials |
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Sponsoring Units: DMP DCOMP GMAG Chair: Richard Hennig, University of Florida Room: LACC 303B |
Wednesday, March 7, 2018 11:15AM - 11:27AM |
L12.00001: Valley Dependent Quantum Anomalous Hall Property in Ferrimagnetic Honeycomb Lattice Jian Zhou , Qiang Sun , Purusottam Jena The valley-polarized quantum anomalous Hall effect (VP-QAHE), which combines valleytronics and topology in one material, is of significant fundamental and practical importance in condensed-matter physics and materials science. In previous model studies, VP-QAHE occurs under strong Rashba spin-orbit coupling (SOC), which is an extrinsic effect. We propose a different mechanism of VP-QAHE by developing a general picture of valley dependent band inversion in honeycomb lattice. Using first-principles calculation, this mechanism is further demonstrated in the Co-In thin film on a Si(111) surface. This system is equivalent to a ferrimagnetic honeycomb lattice. The underlying physical mechanism is generally applicable, opening a new avenue for exploration of substrate supported VP-QAHE. |
Wednesday, March 7, 2018 11:27AM - 11:39AM |
L12.00002: Novel Rare-Earth Magnetic Nitride Perovskites Jose Flores Livas , Rafael Sarmiento-Perez , Silvana Botti , Stefan A Goedecker , Miguel A. L. Marques In this talk, we present perovskite nitrides with magnetic rare-earth metals as novel materials for magnetic applications. These materials appear to be thermodynamically stable and, in spite of possessing different crystal structures and different atomic environments, they retain the magnetic moment of the corresponding elemental rare-earth metal. We find both magnetic metals and semiconductors, with a wide range of magnetic moments and record high magnetic anisotropy energies. Further tuning of the electronic and magnetic properties can also be expected by doping with other rare-earths or by creating solid solutions. |
Wednesday, March 7, 2018 11:39AM - 11:51AM |
L12.00003: Enhancement of magnetic properties of Y_{2}C by increasing degree of localization of anionic electrons Chandani Nandadasa , Kimoon Lee , Jongho Park , Sung Wng Kim , Seong-Gon Kim The existence and evolution of magnetic properties of two-dimensional (2D) electride, Y_{2}C have been investigated using density functional theory within generalized gradient approximation. To investigate the variation of magnetic properties, a few structures with different c-axis parameters around the equilibrium value were considered. Increment of both charge and magnetization density at the interstitial site as the c-axis parameter decreases implies enhancement of the degree of localization of anionic electrons. Furthermore, the radii of the localized anionic electrons were determined from the Bader volume assigned to the interstitial sites. We observed an increase in degree of localization of anionic electrons while compressing the c-axis parameter. Exchange splitting was used to study the origin and enhancement of magnetic properties of equilibrium and deformed structures. Our calculated results confirm the main source of exchange splitting in optimized Y_{2}C is from anionic electrons and not from Y or C. The exchange splitting of anionic electrons increases while decreasing the c-axis parameter. Stoner-type ferromagnetic instability exists in optimized Y_{2}C and the Stoner parameter increases with shrinking c-values. |
Wednesday, March 7, 2018 11:51AM - 12:03PM |
L12.00004: High Throughput Design of Magnetic Materials Hongbin Zhang , Ingo Opahle , Harish Singh , Dominik Ohmer Magnetic materials play an essential role in green energy applications as they provide an efficient |
Wednesday, March 7, 2018 12:03PM - 12:15PM |
L12.00005: The anamolous antiferromagnetic topological phase in pressurized SmB_{6} Peng-Jen Chen , Kai-Wei Chang It is well known that the topological surface states (TSSs) of a topological insulator (TI) are protected by the time-reversal symmetry (TRS). Systems with broken TRS, however, can still host the TSSs if they remain invariant under the combined symmetry operation S = ΘT_{1/2}, where Θ is the TRS operator and T_{1/2} is the translation operation along a crystal axisby half of the corresponding lattic constant [1]. Here, for the first time, we demonstrate that the pressurized SmB_{6} can possibly be classified into the antiferromagnetic topological systems (AFTSs). In addition to propose the possible candidacy for being an AFTS, in this work we also illustrate the anomalous TSSs in an AFTS which is not discussed in the original work. Originating from the interplay between the topological properties and the antiferromagnetic surface magnetization, the topological surface states of the AFT phase behave differently as compared with those of a topological insulator. Besides, the AFT insulators are also found promising in the generation of tunable spin currents, which is an important application in spintronics. |
Wednesday, March 7, 2018 12:15PM - 12:27PM |
L12.00006: Firefly Algorithm Applied to Non-collinear Magnetic Materials Prediction Adam Payne , Guillermo Avendaño-Franco , Eric Bousquet , Aldo Romero Computational materials prediction has become an important technique for the experimental realization of material systems. These predictive methods are based on searching over possible configurations in parameter space. While the optimization of structural parameters has been successful [1], optimization of magnetic parameters has proven to be more challenging, as magnetic systems support a large number of metastable states [2], so calculations are prone to falling into one of these states. In this talk the generalization of the population-based metaheuristic firefly algorithm (FA) [1] to the problem of magnetic ground state prediction in non-collinear magnets will be presented. We extend the different steps of FA to this problem by using polarized density functional theory calculations with the use of Lagrange multipliers to fix the directions of the atomic magnetic moments. This allows for the exploration of the entire Born-Oppenheimer energy surface. Through applications to molecular magnets and magnetic crystals, we demonstrate that the number of minima can be large, which restrains the use of exhaustive searches. |
Wednesday, March 7, 2018 12:27PM - 12:39PM |
L12.00007: Type-II nodal line in RuSb and TaB2 compounds Armindo Cuamba , Lei Hao , Hong-Yan Lu , Chin-Sen Tang In this work, we investigate the topological property and electronic structure of RuSb compound using the first-principles method. The band structure of RuSb without spin-orbit coupling (SOC) exhibits four nodal lines located at the mirror plane kz=0 and the energy of nodal points changes along the nodal line. The tilting of the nodal line located at kz=0 changes which leads to the realization of a mixture of type-I and type-II or hybrid nodal lines. These nodal lines are highly anisotropic and are protected by the mirror symmetry when SOC is ignored. The inclusion of SOC leads to the formation of small gaps along the nodal lines. The corresponding Fermi surface sheets with and without SOC were obtained. The surface states calculation shows the existence of nontrivial surface states characteristic of this material. We also identified the TaB_{2} as the type-II and hybrid nodal line structure. |
Wednesday, March 7, 2018 12:39PM - 12:51PM |
L12.00008: Type-II Dirac Line node in the anti-ReO3 class of materials. Dongwook Kim , Jisoon Ihm , Youngkuk Kim Since the discovery of topological insulator (TI), the topology of electronic band structure has attracted much attention, leading to the discovery of diverse topological materials both in band insulating topological phases and semi-metal phases. In this talk, using first-principles calculations, we show type-II Dirac line node (DLN) can occur in anti-ReO3 class of materials under a mechanical strain. We then discuss the velocity-inversion conditions that classify Dirac line nodes into type-I and type-II, in a similar way to the classification of type-I and type-II Weyl semimetals. |
Wednesday, March 7, 2018 12:51PM - 1:03PM |
L12.00009: Pursuing consensus in the structural modeling of slab-Bi2Se3 for Density Functional Theory Thomas Reid , Sanjeev Nayak , Pamir Alpay Electronic structure calculations in the framework of density functional theory (DFT) have been integral for the study of Bi_{2}Se_{3} as a topological insulator. However, as yet, no consensus on the details of the structural model (on which such calculations would be conducted) has been agreed upon. In this work, we attempt to lay additional groundwork for this consensus, in which we present a comprehensive set of Bi_{2}Se_{3 }slab-models, constructed by systemically modulating salient input parameters, and the calculated electronic bandstructures of each. Then, we offer recommendations for the selection of a given model for DFT calculations, based on a variety of factors, from the set we built. |
Wednesday, March 7, 2018 1:03PM - 1:15PM |
L12.00010: Fe-cluster compounds of chalcogenides: candidates for rare-earth-free permanent magnet and magnetic nodal-line topological material Xin Zhao , Cai-Zhuang Wang , Minsung Kim , Kai-Ming Ho Fe-cluster based crystal structures are predicted for chalcogenides Fe_{3}X_{4} (X = S, Se, Te) using adaptive genetic algorithm. Topologically different from the well-studied layered structures of iron chalcogenides, the newly predicted structures consist of Fe clusters which are either separated by the chalcogen atoms or connected via sharing the vertex Fe atoms. Using first-principles calculations, we demonstrate that these structures have competitive or even lower formation energies than the experimentally synthesized Fe_{3}X_{4} compounds and exhibit interesting magnetic and electronic properties. In particular, we show Fe_{3}Te_{4} can be a good candidate for rare-earth free permanent magnet and Fe_{3}S_{4} can be a magnetic nodal-line topological material. |
Wednesday, March 7, 2018 1:15PM - 1:27PM |
L12.00011: Quantum Anomalous Hall Effect and Conetronics Menghao Wu Based on recently synthesized Ni_{3}C_{12}S_{12}–class 2D metal-organic frameworks (MOFs), we predict electronic properties of M_{3}C_{12}S_{12} and M_{3}C_{12}O_{12}, where M=Zn, Cd, Hg, Be, or Mg with no M orbital contributions to bands near Fermi level. For M_{3}C_{12}S_{12}, their band structures exhibit double Dirac cones with different Fermi velocities that are n (electron) and p (hole) type, respectively, which are switchable by few-percent strain. The crossing of two cones are symmetry-protected to be non-hybridizing, leading to two independent channels in 2D node-line semimetals at the same k-point akin to spin-channels in spintronics, rendering “conetronics” device possible. Quantum anomalous Hall effect can arise in MOFs with non-negligible spin-orbit coupling like Cu3C12O12. We also propose that LaCl and LaBr monolayer and bulk forms, which were fabricated decades ago, can both exhibit intrinsic quantum anomalous Hall effect with an energy gap up to 36meV. These simple binary compounds are revealed to be ferromagnets and their estimated Curie temperature is higher than 400K. Along with the energy gap, the large Curie temperature guarantees that the quantum anomalous Hall effect survives at room-temperature. |
Wednesday, March 7, 2018 1:27PM - 1:39PM |
L12.00012: Theoretical Study of Half-Quantized Spontaneous Vortices in d-dot using 3-D Finite Element Method Model Norio Fujita , Masaru Kato , Takekazu Ishida A d-dot is a nano-sized composite structure that consists of a d-wave superconductor (SC) embedded in an s-wave matrix. Since the phase of the superconducting order parameter in the d-wave SC depends on direction, phase difference appears at the corner junctions between d- and s-wave SCs in d-dots. Due to quantization of fluxoids including this phase difference, spontaneous half-quantized vortex (SHQV) appears at each corner in d-dots. [1]. Basic mechanism of SHQVs is studied theoretically [1] and some experiments observed appearance of SHQVs [2]. Since previous calculation model of d-dot [1] is 2-dimensional, it cannot take account of effects of 3-dimensional structure and defects. So, we extend previous model into 3-D model using volume coordinates with the finite element method (FEM). In this study, by using 3-D d-dot FEM model, we investigate the conditions of appearance of SHQV from viewpoints of c-axis anisotropy. [1] M. Kato, T. Ishida, T. Koyama, M. Machida, Superconductors – Materials, Properties and Applications. (InTech 2012) Chap. 13. [2] H. Hilgenkamp, et al. Nature 422, 50 (2003). |
Wednesday, March 7, 2018 1:39PM - 1:51PM |
L12.00013: Predicted Novel Superconductivity in Compressed Hydrides Hanyu Liu , Ivan Naumov , R Hoffmann , Neil Ashcroft , Russell Hemley The mechanisms for the strong electron-phonon coupling predicted for hydrogen-rich alloys with high superconductivity critical temperature were examined within the Bardeen-Schrieffer-Cooper and Midgal-Eliashberg theory. In this work, we have explored some candidate structures for hydrides at high pressures. Electron-phonon coupling calculations predict the existence of new superconducting phases, some exhibiting superconductivity in the range of room temperature. Further analysis shows that the hydrogen-hydrogen bonding played an important role in determining electron-phonon coupling parameters. Moreover, the calculated stabilities indicate the materials could be synthesized at pressures that are currently accessible in the laboratory. The results open the prospect for the design, synthesis, and recovery of new high-temperature superconductors with potential practical applications. |
Wednesday, March 7, 2018 1:51PM - 2:03PM |
L12.00014: Square selenene and tellurene: new members of elemental 2D materials with nontrivial topological properties Lede Xian , Alejandro Pérez Paz , Elisabeth Bianco , Pulickel Ajayan , Angel Rubio Elemental 2D materials are the simplest form of 2D materials, which consist of only one type of chemical elements. Yet these simple materials have various interesting properties that could lead to promising applications in a board range of fields. Many of the elemental 2D materials composed by elements from groups III to V have been predicted and even synthesized. However, few studies have been reported on the elemental 2D materials from group VI. In this talk, we will introduce two new members of elemental 2D materials composed by group VI elements Se and Te that we call square selenene and square tellurene, respectively. With first principles calculations, we predict that they have chair-like buckled structures in a square unit. This special structure gives rise to anisotropic band dispersions near the Fermi level that can be described by a generalized semi-Dirac Hamiltonian. We show that the considerably large band gap (~0.1 eV) opened by spin-orbit coupling in these materials makes them topological insulators, hosting non-trivial edge states. Finally, we show that this new type of elemental 2D materials can potentially be grown on proper substrates, such as a Au(100) surface. Our study extends the knowledge of elemental 2D materials to the group VI elements. |
Wednesday, March 7, 2018 2:03PM - 2:15PM |
L12.00015: Existence, Engineering, and Stability of Chiral Flat Bands Ajith Ramachandran , Alexei Andreanov , Sergej Flach We study flat bands in bipartite tight-binding networks with discrete translational invariance. Chiral flat bands with chiral symmetry eigenenergy E = 0 and host compact localized eigenstates for finite range hopping. For a bipartite network with a majority sublattice chiral flat bands emerge. We present a simple generating principle of chiral flat-band networks and as a showcase add to the previously observed cases a number of new potentially realizable chiral flat bands in various lattice dimensions. Chiral symmetry respecting network perturbations-including disorder and synthetic magnetic fields-preserve both the flat band and the modified compact localized states. Chiral flat bands are spectrally protected by gaps and pseudogaps in the presence of disorder due to Griffiths effects. |
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