Bulletin of the American Physical Society
APS March Meeting 2018
Volume 63, Number 1
Monday–Friday, March 5–9, 2018; Los Angeles, California
Session L10: Strong Interactions in Topological SemimetalsFocus

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Sponsoring Units: DMP Chair: Vidya Madhavan, University of Illinois at UrbanaChampaign Room: LACC 301B 
Wednesday, March 7, 2018 11:15AM  11:51AM 
L10.00001: Induced Superconductivity in Weyl Semimetals Invited Speaker: Matthew Gilbert The theoretical predictions and subsequent experimental realization of Weyl semimetals has made these interesting materials the subject of intense research. Amongst the open questions in Weyl semimetals, one of the more intriguing concerns the interplay between Weyl semimetals and superconductivity. In this invited presentation, we discuss the various types of induced superconductivity that can be found in both inversionsymmetric or timereversal symmetric Weyl semimetals either by induced by proximity coupling different superconductors, either swave or dwave, or via bulk doping of the Weyl semimetal. Additionally, we also discuss different experimental measurements that can be performed to reveal fundamental properties of these interesting superconducting states. 
Wednesday, March 7, 2018 11:51AM  12:03PM 
L10.00002: Superconducting Proximity Effect in Cd_{3}As_{2} Hybrid Devices Luca Galletti, Timo Schumann, David Kealhofer, Honggyu Kim, Manik Goyal, Susanne Stemmer Dirac semimetals exhibits unique electronic structures, featuring threedimensional bulk Dirac nodes and unconventional surface states. The possibility of opening a gap in the density of states in the bulk opens up to possibility to directly probe topological protected surface state using transport measurements. Furthermore, interfaces with conventional superconductors allow for studying proximity effects, and, potentially, topological superconductivity. Epitaxial Aluminum has been demonstrated to induce hard gap in coplanar junctions in InAs nanowires and quantum wells^{1}, thanks to the high transparency of the interface, which minimizes the quasiparticle poisoning. Here, we present transport measurement on Cd_{3}As_{2} thin films. Quantum oscillations and Hall effect measurements conclusively show that in sufficiently thin films, the transport is carried by the surface states, with a negligible contribution of the bulk. We demonstrate the growth of epitaxial aluminum to induce a superconducting gap in the material by proximity effect. We present measurements of the currentvoltage characteristics of these hybrid junctions. 
Wednesday, March 7, 2018 12:03PM  12:15PM 
L10.00003: Proximity induced superconductivity on the surface of nodal line Weyl semimetals Enrico Rossi, Xiang Hu In this work we study the nature of the superconducting pairing induced by proximity on the surface of Weyl semimetals (WSM) with nodal lines in WSMsuperconductor heterostructures. The surface of a nodal line WSM is characterized by the presence of topologically protected "drumhead'' surface states whose Fermi surfaces are the projection on the surface of the WSM nodal lines. We study how symmetry breaking terms that preserve the nodal line character of the WSM affect the symmetry of the induced superconducting pairing on the surface of the WSM and the effect of orbitaldependent tunneling. We then discuss the concrete case of a heterostructure formed by a nodal line WSM and an swave superconductor with Rashba spinorbit coupling. 
Wednesday, March 7, 2018 12:15PM  12:27PM 
L10.00004: Transverse shift in Andreev reflection Ying Liu, Zhiming Yu, Shengyuan Yang An incoming electron is reflected back as a hole at a normalmetal–superconductor interface, a process known as Andreev reflection. We predict that there exists a universal transverse shift in this process due to the effect of spinorbit coupling in the normal metal. Particularly, using both the scattering approach and the argument of angular momentum conservation, we demonstrate that the shifts are pronounced for lightly doped Weyl semimetals, and are opposite for incoming electrons with different chirality, generating a chiralitydependent Hall effect for the reflected holes. The predicted shift is not limited to Weyl systems, but exists for a general threedimensional spinorbitcoupled metal interfaced with a superconductor. 
Wednesday, March 7, 2018 12:27PM  12:39PM 
L10.00005: Josephson currents on the surface of line Weyl semimetals Xiang Hu, Dmitry Pikulin, Enrico Rossi In line Dirac semimetals (SMs) the bulk conduction and valence bands touch along a line, typically a ring. One of the key properties of line Dirac SMs is to have "drumhead'' surface states, i.e. surface states with a very large effective mass. In the presence of certain types of spinrotation symmetry breaking perturbations the Dirac rings split into Weyl rings. In this work, we study the properties of Josephson junctions formed by two superconductors separated by a line Weyl SM in the limit in which the effect of the bulk states of the Weyl SM can be neglected. In this limit the drumhead states mediate the Josephson current between the two superconductors. We first investigate the Andreev reflection between drumhead surface states and a superconductor and show the relation between the strength of the Andreev reflection and the effective mass of the drumhead states. We then obtain the Josephson current for both short and long junctions for the 
Wednesday, March 7, 2018 12:39PM  12:51PM 
L10.00006: Dirac State in a Centrosymmetric Superconductor αPdBi_{2} Klauss Dimitri, Md Mofazzel Hosen, Gyanendra Dhakal, Hongchul Choi, Firoza Kabir, Dariusz Kaczorowski, Tomasz Durakiewicz, JianXin Zhu, Madhab Neupane Topological superconductor (TSC) hosting Majorana fermions has been established as a milestone that may shift our scientific trajectory from research to applications in topological quantum computing. Recently, superconducting PdBi binaries have attracted great attention as a possible medium for TSC phase as a result of their large spinorbit coupling strength. Here, we report a systematic highresolution angleresolved photoemission spectroscopy (ARPES) study on the normal state electronic structure of superconducting α PdBi_{2} (T_{c} = 1.7 K). Our results show the presence of Dirac states at higherbinding energy with the location of the Dirac point at 1.26 eV below the chemical potential at the zone center. Furthermore, the ARPES data indicate multiple band crossings at the chemical potential, consistent with a metallic behavior of α PdBi_{2}. Our detailed experimental studies are complemented by firstprinciples calculations, which reveal the presence of surface Rashba states residing in the vicinity of the chemical potential. 
Wednesday, March 7, 2018 12:51PM  1:03PM 
L10.00007: Massive Relativistic Spin3/2 RaritaSchwinger Quasiparticle in Condensed Matter Systems Xiangang Wan We study the possibility to realize the massive relativistic spin3/2 RaritaSchwinger (RS) quasiparticles in condensed matter systems (CMS). The main obstacle to be jumped is the nontrivial constraints that eliminate the redundant degrees of freedom in the representation of the Poincar'e group. We propose a generic method to construct a Hamiltonian which automatically contains the RS constraints, and prove that the RS modes always exist and can be separated from the other nonRS ones. Focusing on the two dimensions (2D), we find a novel property for this RS quasiparticle: Due to the nontrivial constraints, although the intrinsic orbital magnetic moment of an energy band is formally like its Berry curvature under symmetry operations, the former is exactly zerovalued in this case despite the latter is finite. Through symmetry considerations, we show that the 2D massive RS quasiparticle can emerge in several trigonal and hexagonal lattices. Based on ab initio calculations, we predict that the thin film of CaLiX (X=Ge and Si) are the candidates. 
Wednesday, March 7, 2018 1:03PM  1:15PM 
L10.00008: Organic diamond lattice Mott insulator: three dimensional Dirac semimetal candidate Yasuhiro Shimizu, Masahisa Tsuchiizu, Akihiro Otsuka, Mitsuhiko Maesato, Yukihiro Yoshida, Gunzi Saito A halffilled Diamond lattice is a promising candidate of threedimensional (3D) topological Dirac semimetal. We report the model material in a molecular compound (ET)Ag_{4}(CN)_{5} with a S=1/2 diamond lattice. The DFT calculation shows Dirac nodal lines with the vanishing density of states at the Fermi energy. Owing to the strong electron correlations, the system exhibits a Mott insulating ground state with antiferromagnet order below 102 K. The weak ferromagnetism indicate the significant spinorbit coupling and inversioin symmetry breaking, which can lift the degeneracy of the nodal line. We report the possible Mott transition into 3D Dirac semimetal under high pressures. 
Wednesday, March 7, 2018 1:15PM  1:27PM 
L10.00009: Weyl rings and enhanced susceptibilities in pyrochlore iridates: $k\cdot p$ analysis of cluster dynamical meanfield theory results Runzhi Wang, Ara Go, Andrew Millis We match analytic results to numerical calculations to provide a detailed picture of the metalinsulator and topological transitions found in density functional plus cluster dynamical meanfield calculations of pyrochlore iridates. We discuss the transition from Weyl metal to Weyl semimetal regimes, and then analyse in detail the properties of the Weyl semimetal phase and its evolution into the topologically trivial insulator. The energy scales in the Weyl semimetal phase are found to be very small, as are the anisotropy parameters. The electronic structure can to a good approximation be described as ‘Weyl rings’ and one of the two branches that contributes to the Weyl bands is essentially flat, leading to enhanced susceptibilities. The optical longitudinal and Hall conductivities are determined; the frequency dependence includes pronounced features that reveal the basic energy scales of the Weyl semimetal phase. 
Wednesday, March 7, 2018 1:27PM  1:39PM 
L10.00010: TomonagaLuttinger liquid and localization in Weyl semimetals XiaoXiao Zhang, Naoto Nagaosa We study both noncentrosymmetric and timereversal breaking Weyl semimetal systems under a strong magnetic field with the Coulomb interaction. The threedimensional bulk system is reduced to many mutually interacting quasionedimensional wires. Each strongly correlated wire can be approached within the TomonagaLuttinger liquid formalism. Introducing impurity scatterings, we inspect the localization effect and the temperature dependence of the electrical resistivity. The effect of a large number of Weyl points in real materials is also included. 
Wednesday, March 7, 2018 1:39PM  1:51PM 
L10.00011: Exotic fermions in condensedmatter systems Baiqing Lyu(Lv), changjiang yi, Zili Feng, Binbin Fu, QuanSheng Wu, Qiunan Xu, Pierre Richard, Junzhang Ma, yaobo huang, V. Strocov, Ming Shi, Chen Fang, Hongming Weng, Youguo Shi, Tian Qian, Hong Ding Condensedmatter systems can host quasiparticle excitations that are analogues to elementary particles such as Majorana, Weyl, and Dirac fermions. Recent advances in band theory have expanded the classification of fermions in crystals, and revealed crystal symmetryprotected electron excitations that have no highenergy counterparts. The first classes of crystal symmetry protected electron excitations without highenergy counterparts are characterized by three, six, or eightfold degenerate points at the Fermi level and named as ‘new fermions’ by Bradlyn et al. While the second types are characterized by one dimensional nodal lines such as nodallink,nodalchain and nodalnet fermions in which more than two nodal lines are connected with each other. Here, using angleresolved photoemission spectroscopy, we demonstrate the existence of threecomponent fermions and nodalnet fermions in solids where the quasiparticle excitations are beyond the MajoranaWeylDirac classification. Our experimental discovery opens up a way of exploring the new physics of unconventional fermions in condensedmatter systems. 
Wednesday, March 7, 2018 1:51PM  2:03PM 
L10.00012: Electronelectron interactions induced phases of Weyl semimetals in strong magnetic fields Simon Bertrand, Rene Cote, Ion Garate Weyl nodes are linear band crossings in a Weyl semimetal which can be seen as "magnetic" monopoles of the Berry Curvature in kspace and they always appear in pairs of opposite "charge", or chirality. As more and more of these materials are discovered with different macroscopic properties (dielectric constant, chemical potential...), it is then crucial to understand if there is any interplay between longrange electronelectron interactions and their topological properties. 
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