Bulletin of the American Physical Society
APS March Meeting 2018
Monday–Friday, March 5–9, 2018; Los Angeles, California
Session C10: Topological Nodal Line and Point SemimetalsFocus

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Sponsoring Units: DMP Chair: Daniel Agterberg, University of WisconsinMilwaukee Room: LACC 301B 
Monday, March 5, 2018 2:30PM  3:06PM 
C10.00001: Triply Degenerate Nodal Point Semimetals Invited Speaker: Hongming Weng , Chen Fang , Zhong Fang , Xi Dai Searching for the analogues of elementary particles in solids has become a hot topic since the discovery of Dirac semimetal (DSM) and Weyl semimetal (WSM). In DSM and WSM, the low energy excitation around the Dirac and Weyl nodes can be described by massless Dirac and Weyl equation, respectively. However, the space group symmetries in solids can protect energy nodes with degeneracy rather than four and two in DSM and WSM, respectively. In this talk, I will introduce our proposals of another nodal point semimetal with triply degenerate nodal points (TDNPs) around the Fermi level. The triple points are the accidental degenerate points of band crossing among a nondegenerate band and a double degenerate bands due to band inversion. The three component fermions are quasiparticles excited from TDNPs. They are intermediate fermions between Dirac and Weyl fermions and have no counterpart in highenergy field theory. The TDNP semimetal can have different longidinal magnetoresistance from DSM and WSM. Some recent experimental observations of TDNPs and magnetoresistance have been also discussed. 
Monday, March 5, 2018 3:06PM  3:18PM 
C10.00002: Observation of bulk nodal lines in topological semimetal ZrSiS Binbin Fu , changjiang yi , Tiantian Zhang , Marco Caputo , Junzhang Ma , Xin Gao , Baiqing Lyu(Lv) , Lingyuan Kong , yaobo huang , Ming Shi , V. Strocov , Chen Fang , Hongming Weng , Youguo Shi , Tian Qian , Hong Ding Topological nodalline semimetals are characterized by protected band crossings along onedimensional route in the Brillouin zone. Crystalline ZrSiS is the most intensively studied topological nodalline semimetal candidate, which is proposed to host multiple nodal lines in its bulk electronic structure. However, previous angleresolved photoemission spectroscopy (ARPES) experiments with vacuum ultraviolet lights mainly probed the surface states. Here using soft Xray ARPES, we acquire the bulk electronic states of ZrSiS without any interference from surface states, unambiguously demonstrating the existence of bulk nodal lines in ZrSiS. Furthermore, our results show that the whole Fermi surfaces are composed of the Dirac nodal lines on highsymmetry planes, as enforced to pin at the Fermi level by carrier compensation. This means that the carriers in ZrSiS are entirely contributed by Dirac nodalline fermions, suggesting that ZrSiS is a remarkable platform for studying physical properties related to nodal lines. 
Monday, March 5, 2018 3:18PM  3:30PM 
C10.00003: Observation of Gapless Dirac Surface States in ZrGeTe Gyanendra Dhakal , Md Mofazzel Hosen , Klauss Dimitri , Alex Aperis , Pablo Maldonado , Ilya Belopolski , Firoza Kabir , Christopher Sims , Zahid Hasan , Dariusz Kaczorowski , Tomasz Durakiewicz , Peter Oppeneer , Madhab Neupane The experimental discovery of the topological Dirac semimetal provides a platform to search for novel exotic quantum phases in real materials. Recently, ZrSiStype materials have been established as topological nodalline semimetals where gapped Diraclike surface states are observed. Here, we present an angleresolved photoemission spectroscopy (ARPES) study of ZrGeTe, a nonsymmorphic symmetry protected Dirac semimetal. We observe two Diraclike gapless surface states at the same X point of the Brillouin zone. Our theoretical analysis and firstprinciples calculations reveal that these are protected by crystalline symmetry. Hence, ZrGeTe appears as a unique example of a naturally fine tuned system where the interplay between symmorphic and nonsymmorphic symmetry leads to rich phenomenology, and thus opens opportunities to investigate the physics of Dirac semimetallic and topological insulating phases realized in a single material. 
Monday, March 5, 2018 3:30PM  3:42PM 
C10.00004: Scanning Tunneling Microscopy of the Topological Dirac Semimetal ZrSiTe Brandon Stuart , Bingkai Yuan , Jisun Kim , Leslie Schoop , Doug Bonn , Sarah Burke Topological Dirac semimetals are interesting for their degenerate linear crossing in the bulk bands, resulting in a range of fascinating electronic properties, such as high electron mobility. Recently, research into Dirac nodalline semimetals, which have a line or loop of linear band crossings within the Brillouin zone, has become abundant in the study of topological materials. Zirconium silicon sulfide (ZrSiS) was shown via ARPES to exhibit a Dirac nodal line crossing approximately 0.5 eV below the Fermi energy [1]. Using this material as a template crystal structure, zirconium silicon telluride (ZrSiTe) was predicted to strain the crystal lattice, pushing the Dirac crossing very near to the Fermi energy [2]. This makes ZrSiTe a perfect candidate to study the Dirac Fermions. Using low temperature (4.5K) STM, we performed scanning tunneling spectroscopy and quasiparticle interference measurements, and I will present data helping to uncover the unique electronic band structure of this material. Furthermore, an outlook into future measurements to elucidate the magnetic and electronic properties of defect atoms using atomic force microscopy will be discussed. [1] Leslie M. Schoop et. al. Nature Communications. (2016). [2] Andreas Topp et. al. New Journal of Physics. (2016). 
Monday, March 5, 2018 3:42PM  3:54PM 
C10.00005: Unusual highfrequency quantum oscillations in topological nodal semimetal ZrSiS Ziji Xiang , Lu Chen , Tomoya Asaba , Colin Tinsman , Yasuyuki Nakajima , Dariusz Kaczorowski , Madhab Neupane , Lu Li The layeredstructured ZrSiS has been confirmed to be a topological nodal semimetal, a family of threedimensional topological material in which the linear band touching forms a onedimensional Dirac linenode. We carried out magnetotransport and torque magnetometry measurement in ZrSiS single crystals. In addition to the multiple small Fermi pockets, we observed two bunches of highfrequency quantum oscillations, with the frequencies in the range of 7.29.1 kT and 10.211.2 kT, respectively. The corresponding electron orbit area is as large as 2030% of the twodimensional Brillouin zone in xyplane. Most intriguingly, these highfrequency oscillations are very sensitive with the tilt angle of applied magnetic field. Their amplitudes can be significantly suppressed by a small tile angle φ ~ 1°. Also, the temperature dependence of oscillation amplitudes shows abnormal nonmonotonic behavior. We suggest that the exotic highfrequency oscillations are related to the Dirac nodal loop in the xyplane. 
Monday, March 5, 2018 3:54PM  4:06PM 
C10.00006: Transport Detection of Surface States in ZrSiSe Thin Flakes Chunlei Yue , Xue Liu , David Graf , Ana Sanchez , Zhiqiang Mao , Jin Hu , Jiang Wei Based on the bulkedge correspondence principle, the observation of topological surface state is regarded as the definitive proof of the nontrivial nature of the bulk band structure in topological semimetals. However, this rule may not apply to topological nodal line semimetals (TNLSM), because the prerequisite of preserving bulk symmetry at the surface may not be satisfied. We investigate this unusual situation in TNLSM ZrSiSe. In this work, we systematically studied the thickness dependence of quantum oscillations in ZrSiSe nanoflakes. With the reducing thickness below 50nm, an additional quantum oscillation emerges. This new quantum oscillation corresponds to a twodimensional (2D) surface state, evidenced by the angular dependence of cos(Θ) in magnetoresistance (AMR) measurements. The analysis of Landau fan diagram and the direct fitting of LifshitzKosevich (LK) formula both suggest a trivial surface state. The estimated size of Fermi surface is in agreement with the ARPES result. Our study verifies exceptional case of bulkedge correspondence principle in TNLSM. And also our experiment demonstrates a new way of probing surface states in TNLSM with nanoscale transport. 
Monday, March 5, 2018 4:06PM  4:18PM 
C10.00007: Crossinglinenode semimetals: general theory and application to rareearth trihydrides Shingo Kobayashi , Youichi Yamakawa , Ai Yamakage , Yoshihiko Okamoto , Yukio Tanaka Topological semimetals are phases of matter with the topological degeneracies near the Fermi level. The topological degeneracies appear as point nodes, line nodes, and surface nodes in the threedimensional Brillouin zone, depending on the contact area between valence and conduction bands. In particular, linenode semimetals have great potential for realizing exotic electronic states. 
Monday, March 5, 2018 4:18PM  4:30PM 
C10.00008: Dirac and Weyl materials with nodal lines Ai Yamakage , Youichi Yamakawa , Katsuhisa Taguchi , Yukio Tanaka , Yoshihiko Okamoto Dirac and Weyl electrons in topological semimetals potentially show exotic electromagnetic responses, while it has not been experimentally discovered yet. For further development, we have proposed ideal candidate materials of nodalline semimetals, CaAgX(X=P,As) [A. Yamakage et al., J. Phys. Soc. Jpn. 85, 013708 (2016); Y. Okamoto and A. Yamakage et al., J. Phys. Soc. Jpn. 85, 123701 (2016); D. Takane and A. Yamakage et al., arXiv:1708.06874] and RH_{3}(R: rare earth) [S. Kobayashi and A. Yamakage et al., Phys. Rev. B 95, 245208 (2017)] that host simple electronic states with torus Fermi surface (line nodes) and without other conventional Fermi surfaces. And spinnondegenerate nodal lines, which appear in PbTaSe_{2}, for instance, are also interesting topological electronic states which can lead to (quasi) topological electromagnetic response such as electric polarization induced by an infinitesimal electric field [S. T. Ramamurthy and T. L. Hughes, Phys. Rev. B 95, 075138 (2017)]. We propose a toy model in which only Weyl nodal lines form the Fermi surface and discuss a building block for Weyl nodal lines and the presence/absence of spinsplit drumhead surface states. 
Monday, March 5, 2018 4:30PM  4:42PM 
C10.00009: Spinless Hourglass Nodalline Semimetals Ryo Takahashi , Motoaki Hirayama , Shuichi Murakami Nodalline semimetal have degeneracy along nodal lines where the band gap is closed. In many cases, the nodal lines appear accidentally, and it is impossible to determine whether the nodal lines appear or not, only from the symmetry and the electron filling. For spinless systems, we show that in specific space groups at 8N+ 4 fillings, presence of the nodal lines is required. In this case the shape of the band structure around these nodal lines is like an hourglass, and we call this a spinless hourglass nodalline semimetal. We establish a list of all the centrosymmetric space groups, under which nonmagnetic spinless systems have hourglass nodal lines, and illustrate where the nodal lines are located. We propose that Al_{3}FeSi_{2} is one of the hourglass nodalline semimetals. Because of inversion symmetry and timereversal symmetry, these nodal lines are also characterized by π Berry phase (or Zak phase). If inversion symmetry is broken, this Zak phase might yield electric polarization. We will discuss polarization after the hourglass nodal lines are gapped out by inversion symmetry breaking. We also discuss some specific materials where the hourglass nodal lines are gapped out by spontaneous breaking of inversion symmetry. 
Monday, March 5, 2018 4:42PM  4:54PM 
C10.00010: Surface and 3D Quantum Hall Effects from Engineering of Exceptional Points in Nodalline Semimetals Jose Gonzalez , Rafael A. Molina We show that, under a strong magnetic field, a 3D nodalline semimetal can be driven into a topological insulating phase with chiral currents flowing along the surface of the material. When the magnetic field is perpendicular to the nodal ring, the surface states of the semimetal are transmuted into Landau states which correspond to exceptional points, i.e. branch points in the spectrum of a nonHermitian Hamiltonian which endow the band structure with a nontrivial topology. When the magnetic field is parallel to the nodal ring, we find that the bulk states are built from the pairing of surfacelike evanescent waves, giving rise to a 3D quantum Hall effect with a flat zeroenergy level of Landau states residing in parallel 2D slices of the 3D material. The transverse Hall conductivity is quantized in either case in units of e^{2}/h, leading in the 3D Hall effect to a number of channels growing linearly with the section of the surface and opening the possibility to observe a macroscopic chiral current at the surface of the material. 
Monday, March 5, 2018 4:54PM  5:06PM 
C10.00011: 3D quantum anomalous Hall effect in a nodeline semimetal Bruno Uchoa , Sang Wook Kim , Kangjun Seo We address the role of interactions for spinless fermions 
Monday, March 5, 2018 5:06PM  5:18PM 
C10.00012: Observation of Nodal Line in NonSymmorphic Topological Semimetal InBi Sandy Adhitia Ekahana , ShuChun Wu , Juan Jiang , K. Okawa , Dharmalingam Prabhakaran , ChanCuk hwang , SungKwan Mo , Takao Sasagawa , Claudia Felser , Binghai Yan , Zhongkai Liu , Yulin Chen Topological nodal semimetal (TNS) is a general term to categorize semimetal whose touching energy bands has a nontrivial topological property. The subset of TNS called topological nodal line semimetal (TNLS) is also predicted where the touching bands form a degenerate onedimension line. These touching bands may also be further protected by its crystal symmetry. In this talk, we will present our work on the bulk and surface electronic structure of the nonsymmorphic TNLS in InBi by using angle resolved photoemission spectroscopy (ARPES). By changing the incoming photon energy, we have tracked the crossing points of the bulk bands and discovered the nodalline feature along the kz direction, in agreement with the abinitio calculations. Our work provides a new material platform for the study of these exotic topological quantum phases and paves the way for possible future applications. 
Monday, March 5, 2018 5:18PM  5:30PM 
C10.00013: Hidden Link, Creation, and Annihilation of Nodal Lines with Z2 Monopole Charges in PTSymmetric Systems Junyeong Ahn , Youngkuk Kim , BohmJung Yang Nodal lines are formed when the conduction and valence bands are inverted if spinorbit coupling is negligible in systems with timereversal T and inversion P symmetries. Those nodal lines have two interesting properties distinguished from nodal points. First, they can have various shapes such as links and knots. Second, they can carry two topological charges: one is the wellknown \pi Berry phase, and the other is the Z2 monopole charge. In this talk, we show that the Z2 monopole charge originates from the exotic hidden link. A nodal line carrying the Z2 monopole charge is always linked to the nodal line formed between the two topmost occupied bands. Then we show how this links of Z2 monopoles can be paircreated by a process we call double band inversion. Finally, we show that paircreation and pairannihilation of nodal lines with Z2 monopole charge can mediate a topological phase transition between a normal insulator and a threedimensional StiefelWhitney insulator (3D SWI). 
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