Bulletin of the American Physical Society
APS March Meeting 2016
Volume 61, Number 2
Monday–Friday, March 14–18, 2016; Baltimore, Maryland
Session R1: 3D Dirac MaterialsInvited

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Sponsoring Units: DCMP Chair: Ady Stern, Weizmann Institute of Science Room: Ballroom I 
Thursday, March 17, 2016 8:00AM  8:36AM 
R1.00001: Weyl Semimetal Phase in Noncentrosymmetric TransitionMetal Monophosphides Invited Speaker: Xi Dai Based on firstprinciple calculations, we show that a family of nonmagnetic materials including TaAs, TaP, NbAs, and NbP are Weyl semimetals (WSM) without inversion centers. We find twelve pairs of Weyl points in the whole Brillouin zone (BZ) for each of them. In the absence of spinorbit coupling (SOC), band inversions in mirrorinvariant planes lead to gapless nodal rings in the energymomentum dispersion. The strong SOC in these materials then opens full gaps in the mirror planes, generating nonzero mirror Chern numbers and Weyl points off the mirror planes. The transport properties obtained by the Boltzmann equation combined with the semiclassical treatments of the unique electronic structure in these materials will also be discussed in comparison with the most recent experimental data. [Preview Abstract] 
Thursday, March 17, 2016 8:36AM  9:12AM 
R1.00002: Chirality transfer dynamics in quantum orbits in the Dirac semimetal Cd$_3$As$_2$ Invited Speaker: Philip Moll 
Thursday, March 17, 2016 9:12AM  9:48AM 
R1.00003: Evidence for the chiral anomaly in the Dirac semimetal Na$_3$Bi Invited Speaker: Jun Xiong Chiral symmetry describes the conservation of handedness of massless chiral fermions in highenergy physics. Such symmetry can be broken by the coexistence of electric ($\vec{E}$) and magnetic ($\vec{B}$) fields, known as the chiral (AdlerBellJackiw) anomaly. This anomaly describes an axial current pumped between lefthanded and righthanded Weyl fermions. In condensed matter physics, the recent development in both theory and experiments has confirmed the existence of Weyl nodes in the Dirac and Weyl semimetals. Generated by the $\vec{E} \cdot \vec{B}$ term, the axial current could induce negative magnetoresistance in the Dirac and Weyl semimetals. Here we report the observation of a large, negative longitudinal magnetoresistance in the Dirac semimetal Na$_3$Bi. By rotating both the direction of $\vec{E}$ and $\vec{B}$, we found that the small deviation of $\vec{E}$ from $\vec{B}$ greatly suppresses the observed negative magnetoresistance. We will discuss its consistency with the predicted chiral anomaly effect in the Dirac/Weyl semimetal. [Preview Abstract] 
Thursday, March 17, 2016 9:48AM  10:24AM 
R1.00004: Experimental realization of new topological phases of matter beyond topological insulators Invited Speaker: Madhab Neupane A threedimensional (3D) Z$_{\mathrm{2\thinspace }}$topological insulator (TI) is a crystalline solid, which is an insulator in the bulk but features spinpolarized Dirac electron states on its surface. In 2007, the first 3D TI was discovered in a bismuthbased compound. The discovery of the first TI tremendously accelerated research into phases of matter characterized by nontrivial topological invariants. Not only did the 3D Z$_{\mathrm{2}}$ TI itself attract great research interest, it also inspired the prediction of a range of new topological phases of matter. The primary examples are the topological Kondo insulator, the topological 3D Dirac and Weyl semimetals, the topological crystalline insulator, topological nodal line semimetal and the topological superconductor. Each of these phases was predicted to exhibit surface states with unique properties protected by a nontrivial topological invariant. In this talk, I will discuss the experimental realization of these new phases of matter in real materials by momentum and timeresolved photoemission spectroscopy. Special attention will be given to the experimental discovery of Dirac semimetal phase in Cd$_{\mathrm{3}}$As$_{\mathrm{2}}$ and topological nodalline phase in PbTaSe$_{\mathrm{2}}$. The unusual properties of the protected topological surface states can lead to potential future applications in spintronics and quantum information, which hold promise to revolutionize our electronics and energy industries. \textit{This work is supported by startup funds from University of Central Florida (MN) and }\textit{Los Alamos National Laboratory LDRD program.} \quad \textit{The work at Princeton and Princetonled ARPES measurements are supported by the Gordon and Betty Moore Foundations EPiQS Initiative through grant GBMF4547 (Hasan) and by U.S. Department of Energy DEFG0205ER46200.} [Preview Abstract] 
Thursday, March 17, 2016 10:24AM  11:00AM 
R1.00005: Timereversal symmetry breaking type II Weyl state in YbMnBi$_{\mathrm{2}}$ Invited Speaker: Sergey Borisenko Detection of Dirac, Majorana and Weyl fermions in real materials may significantly strengthen the bridge between highenergy and condensedmatter physics. While the presence of Dirac fermions is well established in graphene and topological insulators, Majorana particles have been reported recently and evidence for Weyl fermions in noncentrosymmetric crystals has been found only a couple of months ago, the ``magnetic'' Weyl fermions are still elusive despite numerous theoretical predictions and intense experimental search. In order to detect a timereversal symmetry breaking Weyl state we designed two materials with Fermi velocities superior to that of graphene and I will present the experimental evidence of realization of such a state in one of them, YbMnBi$_{\mathrm{2}}$. We model the time reversal symmetry breaking observed by magnetization measurements by a canted antiferromagnetic state and find a number of Weyl points both above and below the Fermi level. Using angleresolved photoemission, we directly observe these latter Weyl points and a hallmark of the exotic state  the arc of the surface states which connects these points. Our results not only provide a fundamental link between the two areas of physics, but also demonstrate the practical way to design novel materials with exotic properties. [Preview Abstract] 
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