Bulletin of the American Physical Society
APS March Meeting 2018
Monday–Friday, March 5–9, 2018; Los Angeles, California
Session P14: Topological Materials  Theory and computationFocus

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Sponsoring Units: DMP Chair: Haizhou Lu, Southern University of Science and Technology, China Room: LACC 304B 
Wednesday, March 7, 2018 2:30PM  3:06PM 
P14.00001: Where are we in the jungle of topological materials? Invited Speaker: Arun Bansil It is just about a decade ago that the quantumspinHall insulator state was observed in HgTe/CdTe quantum wells, followed by the realization of the 3D topological insulator state in BiSb alloys. These discoveries launched an intense worldwide effort on topological states protected by timereversal symmetry constraints and the associated exotic phenomena, leading to the Nobel Prize in physics in 2016. Last few years have seen a great expansion of the field, which now encompasses protected states of quantum matter that arise through combinations of timereversal, crystalline and particlehole symmetries. Despite these advances, the field is still in its infancy and many more surprises can be expected involving 2D and 3D topological materials and their interfaces and heterostructures with magnetic, nonmagnetic and superconducting materials. I will highlight some of the progress that has been made, including our own recent work [16], and comment on the outstanding open questions. 
Wednesday, March 7, 2018 3:06PM  3:18PM 
P14.00002: SymmetryBased Indicators of Band Topology I: Formalism Hoi Chun Po, Haruki Watanabe, Ashvin Vishwanath We develop an efficient theory to answer one of the oldest questions in band theory, namely, what are the possible symmetryrespecting ways to connect energy bands across the Brillouin zone? We find solutions for all 1,651 magnetic space groups in 3D, from which we extract fundamental physical quantities, like the minimal number of electrons required to form a band insulator, and how nontrivial band topology may be reflected in the symmetry eigenvalues. 
Wednesday, March 7, 2018 3:18PM  3:30PM 
P14.00003: SymmetryBased Indicators of Band Topology II: Applications HARUKI WATANABE, Hoi Chun Po, Ashvin Vishwanath How do the symmetry representation of band structures relate to band topology? For space groups with inversion symmetry, the FuKane formula determines the strong/weak index of a band structure based on the parity eigenvalues of the occupied bands. We generalize the relation between symmetry representation and band topology to all 230 space groups and further to all 1651 magnetic space groups. Examples of nontrivial band topology indicated by symmetry representation include topological insulators, (mirror) Chern insulators, and even Weyl/nodal line semimetals. In particular, two copies of a strong topological insulator turns out to be still nontrivial in the presence of inversion symmetry. In this talk, we will discuss these interesting examples in detail. 
Wednesday, March 7, 2018 3:30PM  3:42PM 
P14.00004: New topological phases and new materials using Topological Quantum Chemistry Maia Vergniory, Barry Bradlyn, Jennifer Cano, Zhijun Wang, Luis Elcoro, Mois Aroyo, Claudia Felser, Andrei Bernevig During this talk, I will examine topological metals and insulators stabilized by any of the 
Wednesday, March 7, 2018 3:42PM  3:54PM 
P14.00005: Predicting and Understanding Quantum Spin Hall Insulators with the Help of Compressed Sensing/SISSO. Carlos Mera Acosta, Runhai Ouyang, Adalberto Fazzio, Matthias Scheffler, Luca Ghiringhelli, Christian Carbogno Quantum Spin Hall insulators (QSHIs), i.e., twodimensional insulators with conducting edge states protected by timereversal symmetry, have attracted considerable scientific interest in recent years. In this work, we perform firstprinciples calculations to compute the Z_{2}invariant for 220 functionalized honeycomblattice materials. Using the recently developed sure independence screening and sparsifying operator (SISSO) method [1], we derive a "map of materials", in which metals, trivial insulators, and QSHIs are spatially separated. The axes of this map are defined by physically meaningful descriptors, i.e., nonlinear functions that only depend on the properties of the material’s constituent free atoms. First, this yields fundamental insights into the mechanisms driving topological transitions. Second, we are able to predict the topological character of materials that are not part of the originally investigated set just from their position on the map (predictive power greater than 95%). By this means, we are able to predict 89 yet unknown QSHIs. 
Wednesday, March 7, 2018 3:54PM  4:06PM 
P14.00006: Topological Markers in Disordered, Amorphous, and Quasicrystalline Materials Using KPM. Daniel Varjas, Pablo PerezPiskunow, Anton Akhmerov We implement the kernel polynomial method (KPM) to investigate the topological properties of two and three dimensional materials without translation invariance. By efficiently calculating topological markers, such as the local Chern number and local magnetoelectric coupling, we assess the topological character of disordered model systems. Furthermore, by calculating surface density of states, the ARPES spectra can be simulated for nonperiodic samples. We use these methods to search for material candidates of amorphous and quasicrystalline topological insulators. 
Wednesday, March 7, 2018 4:06PM  4:18PM 
P14.00007: Topological Electrides and Quantized Zak Phase Motoaki Hirayama, Satoru Matsuishi, Hideo Hosono, Shuichi Murakami Recent studies on the topology of the band structure in the kspace have revealed possibilities of various topological insulators and topological semimetals. Here, the topological semimetals include the Dirac semimetals, the Weyl semimetals [1,2], and the nodalline semimetals [1,3]. In my presentation, we show that electrides are suitable for achieving various topological insulating and topological semimetal phases. We present an example of an electride showing the topologically insulating phase characterized by the \pi Zak phase. This can be considered as a limit of the topological nodalline semimetal [3] like calcium, where the Zak phase is either \pi or 0 depending on the momentum regions divided by the nodal lines. This \pi Zak phase appears as a surface polarization charge, and we propose that this surface charge is useful for carrier doping by using the electride. We also talk about the materials having other topological phases such as a nodalline semimetal. [1] S. Murakami, M. Hirayama, R. Okugawa, and T. Miyake, Sci. Adv. 3 e1602680 (2017). [2] M. Hirayama, R. Okugawa, S. Ishibashi, S. Murakami, and T. Miyake, Phys. Rev. Lett. 114, 206401 (2015). [3] M. Hirayama, R. Okugawa, T. Miyake, and S. Murakami, Nat. Commun. 8, 14022 (2017). 
Wednesday, March 7, 2018 4:18PM  4:30PM 
P14.00008: Chiral Topological Excitons in a Chern Band Insulator Ke Chen, Ryuichi Shindou A family of semiconductors called Chern band insulators are shown to host exciton bands with nonzero topological Chern integers and chiral exciton edge modes. Using a prototypical twoband Chern insulator model, we calculate a linear response function among the density and pseudospin degrees of freedom to obtain the exciton bands and their Chern integers. Eigenvalues of the matrixformed response function have a welldefined pole below the electronhole continuum, which describes an energymomentum dispersion for exciton excitations in the Chern insulator. We define a topological Chern integer for exciton bands from the corresponding eigenvectors. The lowest exciton band acquires the Chern integers such as ±1 and ±2 in the electronic Chern insulator phase. The nontrivial topology can be experimentally observed both by a nonlocal optoelectronic response of exciton edge modes and by a phase shift in the crosscorrelation response due to the bulk mode. Our result suggests that magnetically doped HgTe, InAs/GaSb quantum wells, and (Bi,Sb)_{2}Te_{3} thin films are promising candidates for a platform of topological excitonics. 
Wednesday, March 7, 2018 4:30PM  4:42PM 
P14.00009: The New Phases due to Symmetry Protected Piecewise Berry Phases Xuele Liu, Girish Agarwal Finding new phase of matter is a fundamental task in physics. Generally, various phases or states of matter (for instance solid/liquid/gas phases) have different symmetries, the phase transitions among them can be explained by Landau’s symmetry breaking theory. The topological phases discovered in recent years show that different phases may have the same symmetry. The different topological 
Wednesday, March 7, 2018 4:42PM  4:54PM 
P14.00010: Antiferromagnetic Chern insulators in noncentrosymmetric systems Kun Jiang, Sen Zhou, Xi Dai, Ziqiang Wang A new class of topological antiferromagnetic (AF) Chern insulators driven by electronic interactions can emerge from twodimensional systems without inversion symmetry. Despite the absence of a net magnetization, 
Wednesday, March 7, 2018 4:54PM  5:06PM 
P14.00011: Majorana Stripe Order at the Surface of a 3D topological Insulator Yoshitomo Kamiya, Akira Furusaki, Jeffrey Teo, GiaWei Chern The effect of interactions in topological states is a topical issue; not only interactionenabled topological phases but also novel symmetrybreaking phases and phase transitions are possible. Here we study the effect of interactions on Majorana zero modes (MZMs) bound to a square lattice of vortices in 2D topological superconductors. In the special neutrality condition, where the usual hybridization term for MZMs is prohibited by symmetry, we show that a minimal model for MZMs can be faithfully mapped to a quantum spin model, which has no sign problem in the worldline quantum Monte Carlo simulation. Guided by an insight from a further duality mapping to a compass model, we demonstrate that the interactions induce a Majorana stripe order spontaneously breaking translational and rotational symmetries. Away from the neutrality condition, mean field theory suggests a quantum critical point induced by hybridization, beyond which a Dirac cone appears in the excitation spectrum. 
Wednesday, March 7, 2018 5:06PM  5:18PM 
P14.00012: Topological cascade lasers for frequency comb generation. Laura Pilozzi, Giulia Marcucci, Claudio Conti Recent progress of topological photonics is enabling their applications in integrated devices. Among these novel light sources, topological lasers, relaying on the special edge states of topological insulators, protected against imperfections and disorder, have been recently proposed. 
Wednesday, March 7, 2018 5:18PM  5:30PM 
P14.00013: Model of twodimensional topological insulators with SuSchriefferHeeger electronlattice coupling Linghua Zhu, Keun Hyuk Ahn We present a model of twodimensional topological insulators, in which electronic states coupled to lattice distortions through the SuSchriefferHeeger mechanism have nontrivial topological properties. Electronic properties of various twin and antiphase boundaries are calculated for the model and compared with the predictions based on topological arguments. 
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