The Weyl-Cartan Space Problem in Purely Affine Theory
NASA Astrophysics Data System (ADS)
von Borzeszkowski, Horst-Heino; Treder, Hans-Jürgen
1997-04-01
According to Poincaré, only the ``epistemological sum of geometry and physics is measurable". Of course, there are requirements of measurement to be imposed on geometry because otherwise the theory resting on this geometry cannot be physically interpreted. In particular, the Weyl--Cartan space problem must be solved, i.e., it must be guaranteed that the comparison of distances is compatible with the Levi-Civita transport. In the present paper, we discuss these requirements of measurement and show that in the (purely affine) Einstein-Schrödinger unified field theory the solution of the Weyl-Cartan space problem simultaneously determines the matter via Einstein's equations. Here the affine field $\\Gamma^ikl$ represents Poincaré's sum, and the solution of the space problem means its splitting in a metrical space and in matter fields, where the latter are given by the torsion tensor $\\Gamma^i_{[kl]}$.
Generalized Weyl-Heisenberg (GWH) groups
NASA Astrophysics Data System (ADS)
Ghaani Farashahi, Arash
2014-09-01
Let be a locally compact group, be a locally compact Abelian (LCA) group, be a continuous homomorphism, and let be the semi-direct product of and with respect to the continuous homomorphism . In this article, we introduce the Generalized Weyl-Heisenberg (GWH) group associate with the semi-direct product group . We will study basic properties of from harmonic analysis aspects. Finally, we will illustrate applications of these methods in the case of some well-known semi-direct product groups.
Coinvariant algebras and fake degrees for spin Weyl groups of classical type
NASA Astrophysics Data System (ADS)
Baltera, Constance; Wang, Weiqiang
2014-01-01
The coinvariant algebra of a Weyl group plays a fundamental role in several areas of mathematics. The fake degrees are the graded multiplicities of the irreducible modules of a Weyl group in its coinvariant algebra, and they were computed by Steinberg, Lusztig and Beynon-Lusztig. In this paper we formulate a notion of spin coinvariant algebra for every Weyl group. Then we compute all the spin fake degrees for each classical Weyl group, which are by definition the graded multiplicities of the simple modules of a spin Weyl group in the spin coinvariant algebra. The spin fake degrees for the exceptional Weyl groups are given in a sequel.
Polytope Contractions within Weyl Group Symmetries
NASA Astrophysics Data System (ADS)
Szajewska, Marzena
2016-09-01
A general scheme for constructing polytopes is implemented here specifically for the classes of the most important 3D polytopes, namely those whose vertices are labeled by integers relative to a particular basis, here called the ω-basis. The actual number of non-isomorphic polytopes of the same group has no limit. To put practical bounds on the number of polytopes to consider for each group we limit our consideration to polytopes with dominant point (vertex) that contains only nonnegative integers in ω-basis. A natural place to start the consideration of polytopes from is the generic dominant weight which were all three coordinates are the lowest positive integer numbers. Contraction is a continuous change of one or several coordinates to zero.
Weyl group orbits on Kac-Moody root systems
NASA Astrophysics Data System (ADS)
Carbone, Lisa; Conway, Alexander; Freyn, Walter; Penta, Diego
2014-11-01
Let D be a Dynkin diagram and let \\Pi =\\{{{α }1},...,{{α }\\ell }\\} be the simple roots of the corresponding Kac-Moody root system. Let h denote the Cartan subalgebra, let W denote the Weyl group and let Δ denote the set of all roots. The action of W on h, and hence on Δ, is the discretization of the action of the Kac-Moody algebra. Understanding the orbit structure of W on Δ is crucial for many physical applications. We show that for i\
Analog of the Peter-Weyl expansion for Lorentz group
NASA Astrophysics Data System (ADS)
Perlov, Leonid
2015-11-01
The expansion of a square integrable function on SL(2, C) into the sum of the principal series matrix coefficients with the specially selected representation parameters was recently used in the Loop Quantum Gravity [C. Rovelli and F. Vidotto, Covariant Loop Quantum Gravity: An Elementary Introduction to Quantum Gravity and Spinfoam Theory (Cambridge University Press, Cambridge, 2014) and C. Rovelli, Classical Quantum Gravity 28(11), 114005 (2011)]. In this paper, we prove that the sum used originally in the Loop Quantum Gravity: ∑ j = 0 ∞ ∑ |m| ≤ j ∑ |n| ≤ j Dj m , j n ( j , τ j ) ( g ) , where j, m, n ∈ Z, τ ∈ C is convergent to a function on SL(2, C); however, the limit is not a square integrable function; therefore, such sums cannot be used for the Peter-Weyl like expansion. We propose the alternative expansion and prove that for each fixed m: ∑ j = m ∞ D j m , j m ( j , τ j ) ( g ) is convergent and that the limit is a square integrable function on SL(2, C). We then prove the analog of the Peter-Weyl expansion: any ψ(g) ∈ L2(SL(2, C)) can be decomposed into the sum: ψ ( g ) = ∑ j = m ∞ j 2 ( 1 + τ 2 ) c j m m D j m , j m ( j , τ j ) ( g ) , with the Fourier coefficients c j m m = ∫ S L ( 2 , C ) ψ ( g ) Dj m , j m j , τ j ( g ) ¯ d g , g ∈ SL(2, C), τ ∈ C, τ ≠ i, - i, j, m ∈ Z, m is fixed. We also prove convergence of the sums ∑ j = |p| ∞ ∑ |m| ≤ j ∑ |n| ≤ j dp m /j 2 Dj m , j n ( j , τ j ) ( g ) , where d|p| m /j 2 = ( j + 1 ) /1 2 ∫ S U ( 2 ) ϕ ( u ) D|p| m /j 2 ( u ) ¯ d u is ϕ(u)'s Fourier transform and p, j, m, n ∈ Z, τ ∈ C, u ∈ SU(2), g ∈ SL(2, C), thus establishing the map between the square integrable functions on SU(2) and the space of the functions on SL(2, C). Such maps were first used in Rovelli [Class. Quant. Grav. 28, 11 (2011)].
Classification of hyperbolic Dynkin diagrams, root lengths and Weyl group orbits
NASA Astrophysics Data System (ADS)
Carbone, Lisa; Chung, Sjuvon; Cobbs, Leigh; McRae, Robert; Nandi, Debajyoti; Naqvi, Yusra; Penta, Diego
2010-04-01
We give a criterion for a Dynkin diagram, equivalently a generalized Cartan matrix, to be symmetrizable. This criterion is easily checked on the Dynkin diagram. We obtain a simple proof that the maximal rank of a Dynkin diagram of compact hyperbolic type is 5, while the maximal rank of a symmetrizable Dynkin diagram of compact hyperbolic type is 4. Building on earlier classification results of Kac, Kobayashi-Morita, Li and Saçlio\\skew3\\tildeg lu, we present the 238 hyperbolic Dynkin diagrams in ranks 3-10, 142 of which are symmetrizable. For each symmetrizable hyperbolic generalized Cartan matrix, we give a symmetrization and hence the distinct lengths of real roots in the corresponding root system. For each such hyperbolic root system we determine the disjoint orbits of the action of the Weyl group on real roots. It follows that the maximal number of disjoint Weyl group orbits on real roots in a hyperbolic root system is 4.
Identity, Affinity, Reality: Making the Case for Affinity Groups in Elementary School
ERIC Educational Resources Information Center
Parsons, Julie; Ridley, Kimberly
2012-01-01
Affinity groups are places where students build connections and process "ouch" moments from their classes. Children talk about the isolation they sometimes feel. The relationships students gain through race-based affinity groups enable them to feel less alone with their emotions and help them build a stronger sense of self. At the same time,…
Affine group formulation of the Standard Model coupled to gravity
Chou, Ching-Yi; Ita, Eyo; Soo, Chopin
2014-04-15
In this work we apply the affine group formalism for four dimensional gravity of Lorentzian signature, which is based on Klauder’s affine algebraic program, to the formulation of the Hamiltonian constraint of the interaction of matter and all forces, including gravity with non-vanishing cosmological constant Λ, as an affine Lie algebra. We use the hermitian action of fermions coupled to gravitation and Yang–Mills theory to find the density weight one fermionic super-Hamiltonian constraint. This term, combined with the Yang–Mills and Higgs energy densities, are composed with York’s integrated time functional. The result, when combined with the imaginary part of the Chern–Simons functional Q, forms the affine commutation relation with the volume element V(x). Affine algebraic quantization of gravitation and matter on equal footing implies a fundamental uncertainty relation which is predicated upon a non-vanishing cosmological constant. -- Highlights: •Wheeler–DeWitt equation (WDW) quantized as affine algebra, realizing Klauder’s program. •WDW formulated for interaction of matter and all forces, including gravity, as affine algebra. •WDW features Hermitian generators in spite of fermionic content: Standard Model addressed. •Constructed a family of physical states for the full, coupled theory via affine coherent states. •Fundamental uncertainty relation, predicated on non-vanishing cosmological constant.
NASA Astrophysics Data System (ADS)
Li, Fei-Ye; Li, Yao-Dong; Yu, Yue; Kim, Yong Baek; Balents, Leon; Chen, Gang
Conventional magnetic orders in Mott insulators are often believed to be trivial as they are simple product states. In this talk, we argue that this belief is not always right. We study a realistic spin model on the breathing pyrochlore lattice. We find that, although the system has a magnetic ordered ground state, the magnetic excitation is rather nontrivial and supports linear band touchings in its spectrum. This linear band touching is a topological property of the magnon band structure and is thus robust against small perturbation. We thus name this magnon band touching as ``Weyl magnon''. Just like the Weyl fermion, the existence of Weyl magnon suggests the presence of chiral magnon surface states. Unlike the surface Fermi arcs for the Weyl fermions, the chiral surface state for Weyl magnon appears at a finite energy due to the bosonic nature of the magnons. Moreover, the external magnetic field only couples to the spins with a Zeeman term and thus can readily shift the Weyl node position. This provides a way to control the Weyl magnon. Our work will inspire a re-examination of the excitation spectrum of many magnetic ordered systems. Chggst@gmail.com.
An affine projection algorithm using grouping selection of input vectors
NASA Astrophysics Data System (ADS)
Shin, JaeWook; Kong, NamWoong; Park, PooGyeon
2011-10-01
This paper present an affine projection algorithm (APA) using grouping selection of input vectors. To improve the performance of conventional APA, the proposed algorithm adjusts the number of the input vectors using two procedures: grouping procedure and selection procedure. In grouping procedure, the some input vectors that have overlapping information for update is grouped using normalized inner product. Then, few input vectors that have enough information for for coefficient update is selected using steady-state mean square error (MSE) in selection procedure. Finally, the filter coefficients update using selected input vectors. The experimental results show that the proposed algorithm has small steady-state estimation errors comparing with the existing algorithms.
NASA Astrophysics Data System (ADS)
Chen, Hsian-Yang; Lam, Ching Hung
2014-06-01
In this paper, we construct explicitly certain moonshine type vertex operator algebras generated by a set of Ising vectors I such that (1) for any e ≠ f ∈ I, the subVOA VOA(e, f) generated by e and f is isomorphic to either U2B or U3C; and (2) the subgroup generated by the corresponding Miyamoto involutions {τe | e ∈ I} is isomorphic to the Weyl group of a root system of type An, Dn, E6, E7 or E8. The structures of the corresponding vertex operator algebras and their Griess algebras are also studied. In particular, the central charge of these vertex operator algebras are determined.
The Purification of a Blood Group A Glycoprotein: An Affinity Chromatography Experiment.
ERIC Educational Resources Information Center
Estelrich, J.; Pouplana, R.
1988-01-01
Describes a purification process through affinity chromatography necessary to obtain specific blood group glycoproteins from erythrocytic membranes. Discusses the preparation of erythrocytic membranes, extraction of glycoprotein from membranes, affinity chromatography purification, determination of glycoproteins, and results. (CW)
European bioclimatic affinity groups: Data-model comparisons
NASA Astrophysics Data System (ADS)
Laurent, J.-M.; François, L.; Bar-Hen, A.; Bel, L.; Cheddadi, R.
2008-03-01
Global vegetation models are remarkably effective when considering large areas such as Europe. However, their accuracy at finer scales remains to be tested. In this paper, we validate the simulation of modern potential vegetation by the CARbon Assimilation In the Biosphere (CARAIB) model in Europe. Then, in order to evaluate the simulation of tree group distributions at a finer scale, in France, we present a comparison between observed distributions, distributions reconstructed from palynological data, and model simulated ranges. The results will help to validate past vegetation simulations. For this analysis, we use Bioclimatic Affinity Groups (BAGs), based on vegetation groups' climatic tolerances and requirements. The CARAIB model was adapted to simulate the net primary productivity (NPP), biomass and range of the arboreal BAGs. In Europe, at a 30' latitude/longitude grid scale, simulated NPP of BAGs are used to define classes of vegetation as being present or absent, with a classification rule, based on Kappa statistics. In France, at a 10' lat./long. scale, a second discriminant analysis, based on Classification And Regression Tree (CART), allows for a similar classification with BAG pollen percentages. At each palynological sampling site, we then compared the simulation to the reconstruction from pollen data. With 30' lat./long. resolution, most thresholds that discriminate NPP into absence or presence classes are low, ranging from 1 to 77 g/m 2. Agreement indices between observed and simulated distributions range from 0.4 to 0.83, with broad scale BAG potential patterns and boundaries being accurately simulated by CARAIB. In France, on the 10' lat./long. scale, pollen percentages correctly account for BAG presence/absence despite non-linear pollen-vegetation relationships. Agreement ratios between observed and reconstructed patterns range from 0.53 to 0.95. At the 10' lat./long. scale, the validation of simulated ranges with pollen data is reliable for 9 of
Tractors, mass, and Weyl invariance
NASA Astrophysics Data System (ADS)
Gover, A. R.; Shaukat, A.; Waldron, A.
2009-05-01
Deser and Nepomechie established a relationship between masslessness and rigid conformal invariance by coupling to a background metric and demanding local Weyl invariance, a method which applies neither to massive theories nor theories which rely upon gauge invariances for masslessness. We extend this method to describe massive and gauge invariant theories using Weyl invariance. The key idea is to introduce a new scalar field which is constant when evaluated at the scale corresponding to the metric of physical interest. This technique relies on being able to efficiently construct Weyl invariant theories. This is achieved using tractor calculus—a mathematical machinery designed for the study of conformal geometry. From a physics standpoint, this amounts to arranging fields in multiplets with respect to the conformal group but with novel Weyl transformation laws. Our approach gives a mechanism for generating masses from Weyl weights. Breitenlohner-Freedman stability bounds for Anti-de Sitter theories arise naturally as do direct derivations of the novel Weyl invariant theories given by Deser and Nepomechie. In constant curvature spaces, partially massless theories—which rely on the interplay between mass and gauge invariance—are also generated by our method. Another simple consequence is conformal invariance of the maximal depth partially massless theories. Detailed examples for spins s⩽2 are given including tractor and component actions, on-shell and off-shell approaches and gauge invariances. For all spins s⩾2 we give tractor equations of motion unifying massive, massless, and partially massless theories.
The thraustochytrids: a protist group with mixed affinities.
Chamberlain, A H; Moss, S T
1988-01-01
The thraustochytrids, a group of marine, monocentric protists are reconsidered phylogenetically drawing upon ultrastructural and biochemical characters. They appear to have affiliations with both heterokont groups and other phyla of marine organisms, but still remain an essentially independent entity. PMID:3395686
Federal Register 2010, 2011, 2012, 2013, 2014
2012-05-14
... From the Federal Register Online via the Government Publishing Office SECURITIES AND EXCHANGE COMMISSION Adrenalina, Affinity Technology Group, Inc., Braintech, Inc., Builders Transport, Incorporated... Adrenalina because it has not filed any periodic reports since the period ended September 30, 2008....
Novel Kac-Moody-type affine extensions of non-crystallographic Coxeter groups
NASA Astrophysics Data System (ADS)
Dechant, Pierre-Philippe; Bœhm, Céline; Twarock, Reidun
2012-07-01
Motivated by recent results in mathematical virology, we present novel asymmetric {Z}[\\tau ]-integer-valued affine extensions of the non-crystallographic Coxeter groups H2, H3 and H4 derived in a Kac-Moody-type formalism. In particular, we show that the affine reflection planes which extend the Coxeter group H3 generate (twist) translations along two-, three- and five-fold axes of icosahedral symmetry, and we classify these translations in terms of the Fibonacci recursion relation applied to different start values. We thus provide an explanation of previous results concerning affine extensions of icosahedral symmetry in a Coxeter group context, and extend this analysis to the case of the non-crystallographic Coxeter groups H2 and H4. These results will enable new applications of group theory in physics (quasicrystals), biology (viruses) and chemistry (fullerenes).
Spacetimes of Weyl and Ricci type N in higher dimensions
NASA Astrophysics Data System (ADS)
Kuchynka, M.; Pravdová, A.
2016-06-01
We study the geometrical properties of null congruences generated by an aligned null direction of the Weyl tensor (WAND) in spacetimes of Weyl and Ricci type N (possibly with a non-vanishing cosmological constant) in an arbitrary dimension. We prove that a type N Ricci tensor and a type III or N Weyl tensor have to be aligned. In such spacetimes, the multiple WAND has to be geodetic. For spacetimes with type N aligned Weyl and Ricci tensors, the canonical form of the optical matrix in the twisting and non-twisting cases is derived and the dependence of the Weyl and the Ricci tensors and Ricci rotation coefficients on the affine parameter of the geodetic null congruence generated by the WAND is obtained.
Affinities of human histo-blood group antigens for norovirus capsid protein complexes
Han, Ling; Kitova, Elena N; Tan, Ming; Jiang, Xi; Pluvinage, Benjamin; Boraston, Alisdair B; Klassen, John S
2015-01-01
The binding profiles of many human noroviruses (huNoVs) for human histo-blood group antigens have been characterized. However, quantitative-binding data for these important virus–host interactions are lacking. Here, we report on the intrinsic (per binding site) affinities of HBGA oligosaccharides for the huNoV VA387 virus-like particles (VLPs) and the associated subviral P particles measured using electrospray ionization mass spectrometry. The affinities of 13 HBGA oligosaccharides, containing A, B and H epitopes, with variable sizes (disaccharide to tetrasaccharide) and different precursor chain types (types 1, 2, 3, 5 and 6), were measured for the P particle, while the affinities of the A and B trisaccharides and A and B type 6 tetrasaccharides for the VLP were determined. The intrinsic affinities of the HBGA oligosaccharides for the P particle range from 500 to 2300 M−1, while those of the A and B trisaccharides and the A and B type 6 tetrasaccharides for the VLP range from 1000 to 4000 M−1. Comparison of these binding data with those measured previously for the corresponding P dimer reveals that the HBGA oligosaccharides tested exhibit similar intrinsic affinities for the P dimer and P particle. The intrinsic affinities for the VLP are consistently higher than those measured for the P particle, but within a factor of three. While the cause of the subtle differences in HBGA oligosaccharide affinities for the P dimer and P particle and those for the VLP remains unknown, the present data support the use of P dimers or P particles as surrogates to the VLP for huNoV-receptor-binding studies. PMID:25395406
Hecke-Clifford Algebras and Spin Hecke Algebras IV: Odd Double Affine Type
NASA Astrophysics Data System (ADS)
Khongsap, Ta; Wang, Weiqiang
2009-01-01
We introduce an odd double affine Hecke algebra (DaHa) generated by a classical Weyl group W and two skew-polynomial subalgebras of anticommuting generators. This algebra is shown to be Morita equivalent to another new DaHa which are generated by W and two polynomial-Clifford subalgebras. There is yet a third algebra containing a spin Weyl group algebra which is Morita (super)equivalent to the above two algebras. We establish the PBW properties and construct Verma-type representations via Dunkl operators for these algebras.
Weyl semimetal state in TaP: experimental discovery
NASA Astrophysics Data System (ADS)
Shibayev, Pavel; Hasan Research Group Team
Despite their extreme rareness in nature, Weyl semimetals provide the first realization of Weyl fermions. After families of tantalum-based (TaAs, TaP) and niobium-based (NbAs, NbP) compounds were recently predicted as Weyl semimetal candidates, our group experimentally realized the Weyl semimetal state in TaP. Angle-resolved photoemission spectroscopy (ARPES) was used to probe the surface features of TaP. Weyl fermion cones and nodes were directly observed in the bulk, and Fermi arcs were observed on the surface. The surface states were found to possess a rich structure, containing topological Fermi arcs and topologically trivial closed contours in the neighborhood of Weyl points. This finding opens up possibilities to study the relationship between trivial and topological surface states on the surface of a Weyl semimetal. By determining the number of chiral edge modes on a closed path enclosing the Weyl node, bulk-boundary correspondence was demonstrated, leading to the establishment of a topologically nontrivial nature of the Weyl semimetal state in TaP. The work at Princeton and Princeton-led ARPES measurements were supported by the Gordon and Betty Moore Foundations EPiQS Initiative through Grant GBMF4547 (Hasan) and by U.S. Department of Energy DE-FG-02-05ER46200.
Mönster, Andrea; Hiller, Oliver; Grüger, Daniela; Blasczyk, Rainer; Kasper, Cornelia
2011-02-01
Monolithic columns have gained increasing attention as stationary phases for the separation of biomolecules and biopharmaceuticals. In the present work the performance of monolithic convective interaction media (CIM(®)) chromatography for the purification of blood group antigens was established. The proteins employed in this study are derived from blood group antigens Knops, JMH and Scianna, equipped both with a His-tag and with a V5-tag by which they can be purified. In a first step a monoclonal antibody directed against the V5-tag was immobilized on a CIM(®) Disk with epoxy chemistry. After this, the immobilized CIM(®) Disk was used in immuno-affinity chromatography to purify the three blood group antigens from cell culture supernatant. Up-scaling of the applied technology was carried out using CIM(®) Tubes. In comparison to conventional affinity chromatography, blood group antigens were also purified via His-tag using a HiTrap(®) metal-affinity column. The two purifications have been compared regarding purity, yield and purification speed. Using the monolithic support, it was possible to isolate the blood group antigens with a higher flow rate than using the conventional bed-packed column. PMID:21194702
Cluster algebra structure on the finite dimensional representations of affine quantum group
NASA Astrophysics Data System (ADS)
Yang, Yan-Min; Ma, Hai-Tao; Lin, Bing-Sheng; Zheng, Zhu-Jun
2015-01-01
In this paper, we prove one case of conjecture given by Hernandez and Leclerc. We give a cluster algebra structure on the Grothendieck ring of a full subcategory of the finite dimensional representations of affine quantum group . As a conclusion, for every exchange relation of cluster algebra, there exists an exact sequence of the full subcategory corresponding to it. Project supported by the National Natural Science Foundation of China (Grant No. 11475178).
Soluyanov, Alexey A; Gresch, Dominik; Wang, Zhijun; Wu, QuanSheng; Troyer, Matthias; Dai, Xi; Bernevig, B Andrei
2015-11-26
Fermions--elementary particles such as electrons--are classified as Dirac, Majorana or Weyl. Majorana and Weyl fermions had not been observed experimentally until the recent discovery of condensed matter systems such as topological superconductors and semimetals, in which they arise as low-energy excitations. Here we propose the existence of a previously overlooked type of Weyl fermion that emerges at the boundary between electron and hole pockets in a new phase of matter. This particle was missed by Weyl because it breaks the stringent Lorentz symmetry in high-energy physics. Lorentz invariance, however, is not present in condensed matter physics, and by generalizing the Dirac equation, we find the new type of Weyl fermion. In particular, whereas Weyl semimetals--materials hosting Weyl fermions--were previously thought to have standard Weyl points with a point-like Fermi surface (which we refer to as type-I), we discover a type-II Weyl point, which is still a protected crossing, but appears at the contact of electron and hole pockets in type-II Weyl semimetals. We predict that WTe2 is an example of a topological semimetal hosting the new particle as a low-energy excitation around such a type-II Weyl point. The existence of type-II Weyl points in WTe2 means that many of its physical properties are very different to those of standard Weyl semimetals with point-like Fermi surfaces. PMID:26607545
NASA Astrophysics Data System (ADS)
Soluyanov, Alexey A.; Gresch, Dominik; Wang, Zhijun; Wu, Quansheng; Troyer, Matthias; Dai, Xi; Bernevig, B. Andrei
2015-11-01
Fermions—elementary particles such as electrons—are classified as Dirac, Majorana or Weyl. Majorana and Weyl fermions had not been observed experimentally until the recent discovery of condensed matter systems such as topological superconductors and semimetals, in which they arise as low-energy excitations. Here we propose the existence of a previously overlooked type of Weyl fermion that emerges at the boundary between electron and hole pockets in a new phase of matter. This particle was missed by Weyl because it breaks the stringent Lorentz symmetry in high-energy physics. Lorentz invariance, however, is not present in condensed matter physics, and by generalizing the Dirac equation, we find the new type of Weyl fermion. In particular, whereas Weyl semimetals—materials hosting Weyl fermions—were previously thought to have standard Weyl points with a point-like Fermi surface (which we refer to as type-I), we discover a type-II Weyl point, which is still a protected crossing, but appears at the contact of electron and hole pockets in type-II Weyl semimetals. We predict that WTe2 is an example of a topological semimetal hosting the new particle as a low-energy excitation around such a type-II Weyl point. The existence of type-II Weyl points in WTe2 means that many of its physical properties are very different to those of standard Weyl semimetals with point-like Fermi surfaces.
Semimetal with both Rarita-Schwinger-Weyl and Weyl excitations
NASA Astrophysics Data System (ADS)
Liang, Long; Yu, Yue
2016-01-01
A relativistic spinor with spin 3/2 is historically called a Rarita-Schwinger spinor. The right- and left-handed chiral degrees of freedom for the massless Rarita-Schwinger spinor are independent and are thought of as the left and right Weyl fermions with helicity ±3 /2 . We study three orbital spin-1/2 Weyl semimetals in the strong spin-orbital coupling limit with time reversal symmetry breaking. We find that in this limit the systems can be a Jeff=1 /2 Weyl semimetal or a Jeff=3 /2 semimetal, depending on the Fermi level position. The latter near Weyl points includes degrees of freedom of both Rarita-Schwinger-Weyl and Weyl. A nonlocal potential separates the Weyl and Rarita-Schwinger-Weyl degrees of freedom, and a relativistic Rarita-Schwinger-Weyl semimetal emerges. This recipe can be generalized to a mulit-Weyl semimetal and Weyl fermions with pairing interaction to obtain high monopole charges. Similarly, a spatial-inversion-breaking Raita-Schwinger-Weyl semimetal may also emerge.
On the Weyl curvature hypothesis
NASA Astrophysics Data System (ADS)
Stoica, Ovidiu Cristinel
2013-11-01
The Weyl curvature hypothesis of Penrose attempts to explain the high homogeneity and isotropy, and the very low entropy of the early universe, by conjecturing the vanishing of the Weyl tensor at the Big-Bang singularity.
Dresner, L.
1987-08-01
Problems of technological interest can very often be described by partial differential equations (PDEs) with one dependent and two independent variables (call them c, z, and t, respectively). Many such PDEs are invariant to one-parameter families of one-parameter affine groups. Similarity solutions are solutions of the PDE that are invariant to one group of the family. The great utility of similarity solutions is that they may be calculated by solving an ODE rather than a PDE and are thus much more easily accessible than other solutions. The form of the principal ODE depends, of course, on the form of the PDE, but it can be proved quite generally that the principal ODE is itself invarient to the one-parameter affine group or associated group. because of the invariance of the principal ODE to the associated group, the dependence on the boundary and initial conditions of certain special values of the function y(x), e.g., y(O), y(infinity), y(O), ets., may be predicted a priori without solving the principal ODE. The nonlinear PDE of heat transport in superfluid He-II, is used as an illustration of these ideas in this review.
Dental affinities of the C-group inhabitants of Hierakonpolis, Egypt: Nubian, Egyptian, or both?
Irish, J D; Friedman, R
2010-04-01
By c. 2050 BC a small community of C-Group Nubians was present deep within Egyptian territory at the city of Hierakonpolis. Their descendants stayed for the next 400 years. Today, the site of Hierakonpolis, 113 km north of Aswan, is known for its Egyptian deposits; however, it also contains a C-Group cemetery, which documents the northernmost occurrence of this culture. Sixty skeletons were excavated. Tombs feature Nubian architecture and goods, including leather garments, although the use of Egyptian mortuary practices and artifacts increased through time. Dates range from the early 11th Dynasty into the Second Intermediate period. During this time the Egyptian empire occupied Lower Nubia, and their state ideology vilified Nubians. Yet, at least in death, the C-Group inhabitants of Hierakonpolis proudly displayed their cultural heritage. Beyond discerning the reason(s) for their presence at the site (e.g., mercenaries, leather-workers, entertainers?), the focus of this report is to estimate their biological affinity. Were they akin to other Nubians, Egyptians, or both? And, was increasing 'Egyptianization' evident in the mortuary ritual accompanied by concomitant genetic influence? To address these queries, up to 36 dental morphological traits in the recovered individuals were compared to those in 26 regional comparative samples. The most influential traits were identified and phenetic affinities were calculated using the mean measure of divergence and other multivariate analyses. Assuming phenetic similarity provides an estimate of genetic relatedness, these affinities suggest the individuals comprising the C-Group sample were, and remained Nubian during their tenure at Hierakonpolis. PMID:20185126
NASA Astrophysics Data System (ADS)
Marino, Eduardo
The electron, discovered by Thomson by the end of the nineteenth century, was the first experimentally observed particle. The Weyl fermion, though theoretically predicted since a long time, was observed in a condensed matter environment in an experiment reported only a few weeks ago. Is there any linking thread connecting the first and the last observed fermion (quasi)particles? The answer is positive. By generalizing the method known as bosonization, the first time in its full complete form, for a spacetime with 3+1 dimensions, we are able to show that both electrons and Weyl fermions can be expressed in terms of the same boson field, namely the Kalb-Ramond anti-symmetric tensor gauge field. The bosonized form of the Weyl chiral currents lead to the angle-dependent magneto-conductance behavior observed in these systems.
Affinities of recombinant norovirus P dimers for human blood group antigens
Han, Ling; Kitov, Pavel I; Kitova, Elena N; Tan, Ming; Wang, Leyi; Xia, Ming; Jiang, Xi; Klassen, John S
2013-01-01
Noroviruses (NoVs), the major cause of viral acute gastroenteritis, recognize histo-blood group antigens (HBGAs) as receptors or attachment factors. To gain a deeper understanding of the interplay between NoVs and their hosts, the affinities of recombinant P dimers (P2's) of a GII.4 NoV (VA387) to a library of 41 soluble analogs of HBGAs were measured using the direct electrospray ionization mass spectrometry assay. The HBGAs contained the A, B, H and Lewis epitopes, with variable sizes (2–6 residues) and different types (1–6). The results reveal that the P2's exhibit a broad specificity for the HBGAs and bind to all of the oligosaccharides tested. Overall, the affinities are relatively low, ranging from 400 to 3000 M−1 and are influenced by the chain type: 3 > 1 ≈ 2 ≈ 4 ≈ 5 ≈ 6 for H antigens; 6 > 1 ≈ 3 ≈ 4 ≈ 5 > 2 for A antigens; 3 > 1 ≈ 4 ≈ 5 ≈ 6 > 2 for B antigens, but not by chain length. The highest-affinity ligands are B type 3 (3000 ± 300 M−1) and A type 6 (2350 ± 60 M−1). While the higher affinity to the type 3 H antigen was previously observed, preferential binding to the types 6 and 3 antigens with A and B epitopes, respectively, has not been previously reported. A truncated P domain dimer (lacking the C-terminal arginine cluster) exhibits similar binding. The central-binding motifs in the HBGAs were identified by molecular-docking simulations. PMID:23118206
Weyl semimetals and topological phase transitions
NASA Astrophysics Data System (ADS)
Murakami, Shuichi
Weyl semimetals are semimetals with nondegenerate 3D Dirac cones in the bulk. We showed that in a transition between different Z2 topological phases, i.e. between the normal insulator (NI) and topological insulator (TI), the Weyl semimetal phase necessarily appears when inversion symmetry is broken. In the presentation we show that this scenario holds for materials with any space groups without inversion symmetry. Namely, let us take any band insulator without inversion symmetry, and assume that the gap is closed by a change of an external parameter. In such cases we found that the system runs either into (i) a Weyl semimetal or (ii) a nodal-line semimetal, but no insulator-to-insulator transition happens. This is confirmed by classifying the gap closing in terms of the space groups and the wavevector. In the case (i), the number of Weyl nodes produced at the gap closing ranges from 2 to 12 depending on the symmetry. In (ii) the nodal line is protected by mirror symmetry. In the presentation, we explain some Weyl semimetal and nodal-line semimetals which we find by using this classification. As an example, we explain our result on ab initio calculation on tellurium (Te). Tellurium consists of helical chains, and therefore lacks inversion and mirror symmetries. At high pressure the band gap of Te decreases and finally it runs into a Weyl semimetal phase, as confirmed by our ab initio calculation. In such chiral systems as tellurium, we also theoretically propose chiral transport in systems with such helical structures; namely, an orbital magnetization is induced by a current along the chiral axis, in analogy with a solenoid.
NASA Astrophysics Data System (ADS)
Soluyanov, Alexey; Gresch, Dominik; Wang, Zhijun; Wu, Quansheng; Troyer, Matthias; Dai, Xi; Bernevig, Andrei
The Dirac equation of quantum field theory gives rise to massless Weyl fermions that respect Lorentz invariance. In condensed matter these fermions are realized as low energy excitations in Weyl semimetals. In these materials a topologically protected linear crossing of two bands, called a Weyl point, occurs at the Fermi level resulting in a point-like Fermi surface. Lorentz invariance, however, can be violated in condensed matter, and here we generalize the Dirac equation accordingly to obtain a fundamentally new kind of Weyl fermions. In particular, we report on a novel type of Weyl semimetal, with a new type of Weyl point that emerges at the boundary between electron and hole pockets. This node, although still a protected crossing, has an open, not point-like, Fermi surface, resulting in physical properties very different from that of standard Weyl points. We show that an established material, WTe2, is an example of this novel type of topological semimetals.
Jones, Gregory; Wang, John E.
2005-06-15
To capture important physical properties of a spacetime we construct a new diagram, the card diagram, which accurately draws generalized Weyl spacetimes in arbitrary dimensions by encoding their global spacetime structure, singularities, horizons, and some aspects of causal structure including null infinity. Card diagrams draw only nontrivial directions providing a clearer picture of the geometric features of spacetimes as compared to Penrose diagrams, and can change continuously as a function of the geometric parameters. One of our main results is to describe how Weyl rods are traversable horizons and the entirety of the spacetime can be mapped out. We review Weyl techniques and as examples we systematically discuss properties of a variety of solutions including Kerr-Newman black holes, black rings, expanding bubbles, and recent spacelike-brane solutions. Families of solutions will share qualitatively similar cards. In addition we show how card diagrams not only capture information about a geometry but also its analytic continuations by providing a geometric picture of analytic continuation. Weyl techniques are generalized to higher dimensional charged solutions and applied to generate perturbations of bubble and S-brane solutions by Israel-Khan rods.
NASA Astrophysics Data System (ADS)
Jones, Gregory; Wang, John E.
2005-06-01
To capture important physical properties of a spacetime we construct a new diagram, the card diagram, which accurately draws generalized Weyl spacetimes in arbitrary dimensions by encoding their global spacetime structure, singularities, horizons, and some aspects of causal structure including null infinity. Card diagrams draw only nontrivial directions providing a clearer picture of the geometric features of spacetimes as compared to Penrose diagrams, and can change continuously as a function of the geometric parameters. One of our main results is to describe how Weyl rods are traversable horizons and the entirety of the spacetime can be mapped out. We review Weyl techniques and as examples we systematically discuss properties of a variety of solutions including Kerr-Newman black holes, black rings, expanding bubbles, and recent spacelike-brane solutions. Families of solutions will share qualitatively similar cards. In addition we show how card diagrams not only capture information about a geometry but also its analytic continuations by providing a geometric picture of analytic continuation. Weyl techniques are generalized to higher dimensional charged solutions and applied to generate perturbations of bubble and S-brane solutions by Israel-Khan rods.
NASA Astrophysics Data System (ADS)
Morimoto, Takahiro; Nagaosa, Naoto
2016-01-01
Relativistic Weyl fermion (WF) often appears in the band structure of three dimensional magnetic materials and acts as a source or sink of the Berry curvature, i.e., the (anti-)monopole. It has been believed that the WFs are stable due to their topological indices except when two Weyl fermions of opposite chiralities annihilate pairwise. Here, we theoretically show for a model including the electron-electron interaction that the Mott gap opens for each WF without violating the topological stability, leading to a topological Mott insulator dubbed Weyl Mott insulator (WMI). This WMI is characterized by several novel features such as (i) energy gaps in the angle-resolved photo-emission spectroscopy (ARPES) and the optical conductivity, (ii) the nonvanishing Hall conductance, and (iii) the Fermi arc on the surface with the penetration depth diverging as approaching to the momentum at which the Weyl point is projected. Experimental detection of the WMI by distinguishing from conventional Mott insulators is discussed with possible relevance to pyrochlore iridates.
Morimoto, Takahiro; Nagaosa, Naoto
2016-01-01
Relativistic Weyl fermion (WF) often appears in the band structure of three dimensional magnetic materials and acts as a source or sink of the Berry curvature, i.e., the (anti-)monopole. It has been believed that the WFs are stable due to their topological indices except when two Weyl fermions of opposite chiralities annihilate pairwise. Here, we theoretically show for a model including the electron-electron interaction that the Mott gap opens for each WF without violating the topological stability, leading to a topological Mott insulator dubbed Weyl Mott insulator (WMI). This WMI is characterized by several novel features such as (i) energy gaps in the angle-resolved photo-emission spectroscopy (ARPES) and the optical conductivity, (ii) the nonvanishing Hall conductance, and (iii) the Fermi arc on the surface with the penetration depth diverging as approaching to the momentum at which the Weyl point is projected. Experimental detection of the WMI by distinguishing from conventional Mott insulators is discussed with possible relevance to pyrochlore iridates. PMID:26822023
Puerta, David T; Lewis, Jana A; Cohen, Seth M
2004-07-14
In an effort to identify promising non-hydroxamate inhibitors of matrix metalloproteinases (MMPs), several new zinc-binding groups (ZBGs) based on pyrone, pyrothione, hydroxypyridinone, and hydroxypyridinethione chelators have been examined. Structural studies with tris(pyrazolyl)borate model complexes show that these ligands bind to the MMP active site zinc(II) ion in a bidentate fashion, similar to that found with hydroxamate-based inhibitors. Fluorescence- and colorimetric-based enzyme assays have been used to determine the IC50 values for these ZBGs against MMP-3; mixed O,S-donor ligands were found to be remarkably potent, with IC50 values as much as 700-fold lower than that found for acetohydroxamic acid. Inhibitory activity was found to parallel metal binding affinity as determined in titrations with model complexes. These results demonstrate that MPIs based on new ZBGs are feasible and may indeed improve the overall performance of inhibitors designed against these important medicinal targets. PMID:15237990
NASA Astrophysics Data System (ADS)
Pellegrino, Francesco M. D.; Katsnelson, Mikhail I.; Polini, Marco
2015-11-01
Helicons are transverse electromagnetic waves propagating in three-dimensional (3D) electron systems subject to a static magnetic field. We present a theory of helicons propagating through a 3D Weyl semimetal. Our approach relies on the evaluation of the optical conductivity tensor from semiclassical Boltzmann transport theory, with the inclusion of certain Berry curvature corrections that have been neglected in the earlier literature (such as the one due to the orbital magnetic moment). We demonstrate that the axion term characterizing the electromagnetic response of Weyl semimetals dramatically alters the helicon dispersion with respect to that in nontopological metals. We also discuss axion-related anomalies that appear in the plasmon dispersion relation.
Holographic thermalization with Weyl corrections
NASA Astrophysics Data System (ADS)
Dey, Anshuman; Mahapatra, Subhash; Sarkar, Tapobrata
2016-01-01
We consider holographic thermalization in the presence of a Weyl correction in five dimensional AdS space. We first obtain the Weyl corrected black brane solution perturbatively, up to first order in the coupling. The corresponding AdS-Vaidya like solution is then constructed. This is then used to numerically analyze the time dependence of the two point correlation functions and the expectation values of rectangular Wilson loops in the boundary field theory, and we discuss how the Weyl correction can modify the thermalization time scales in the dual field theory. In this context, the subtle interplay between the Weyl coupling constant and the chemical potential is studied in detail.
New type of Weyl semimetal with quadratic double Weyl fermions.
Huang, Shin-Ming; Xu, Su-Yang; Belopolski, Ilya; Lee, Chi-Cheng; Chang, Guoqing; Chang, Tay-Rong; Wang, BaoKai; Alidoust, Nasser; Bian, Guang; Neupane, Madhab; Sanchez, Daniel; Zheng, Hao; Jeng, Horng-Tay; Bansil, Arun; Neupert, Titus; Lin, Hsin; Hasan, M Zahid
2016-02-01
Weyl semimetals have attracted worldwide attention due to their wide range of exotic properties predicted in theories. The experimental realization had remained elusive for a long time despite much effort. Very recently, the first Weyl semimetal has been discovered in an inversion-breaking, stoichiometric solid TaAs. So far, the TaAs class remains the only Weyl semimetal available in real materials. To facilitate the transition of Weyl semimetals from the realm of purely theoretical interest to the realm of experimental studies and device applications, it is of crucial importance to identify other robust candidates that are experimentally feasible to be realized. In this paper, we propose such a Weyl semimetal candidate in an inversion-breaking, stoichiometric compound strontium silicide, SrSi2, with many new and novel properties that are distinct from TaAs. We show that SrSi2 is a Weyl semimetal even without spin-orbit coupling and that, after the inclusion of spin-orbit coupling, two Weyl fermions stick together forming an exotic double Weyl fermion with quadratic dispersions and a higher chiral charge of ±2. Moreover, we find that the Weyl nodes with opposite charges are located at different energies due to the absence of mirror symmetry in SrSi2, paving the way for the realization of the chiral magnetic effect. Our systematic results not only identify a much-needed robust Weyl semimetal candidate but also open the door to new topological Weyl physics that is not possible in TaAs. PMID:26787914
New type of Weyl semimetal with quadratic double Weyl fermions
Huang, Shin-Ming; Xu, Su-Yang; Belopolski, Ilya; Lee, Chi-Cheng; Chang, Guoqing; Chang, Tay-Rong; Wang, BaoKai; Alidoust, Nasser; Bian, Guang; Neupane, Madhab; Sanchez, Daniel; Zheng, Hao; Jeng, Horng-Tay; Bansil, Arun; Neupert, Titus; Lin, Hsin; Hasan, M. Zahid
2016-01-01
Weyl semimetals have attracted worldwide attention due to their wide range of exotic properties predicted in theories. The experimental realization had remained elusive for a long time despite much effort. Very recently, the first Weyl semimetal has been discovered in an inversion-breaking, stoichiometric solid TaAs. So far, the TaAs class remains the only Weyl semimetal available in real materials. To facilitate the transition of Weyl semimetals from the realm of purely theoretical interest to the realm of experimental studies and device applications, it is of crucial importance to identify other robust candidates that are experimentally feasible to be realized. In this paper, we propose such a Weyl semimetal candidate in an inversion-breaking, stoichiometric compound strontium silicide, SrSi2, with many new and novel properties that are distinct from TaAs. We show that SrSi2 is a Weyl semimetal even without spin–orbit coupling and that, after the inclusion of spin–orbit coupling, two Weyl fermions stick together forming an exotic double Weyl fermion with quadratic dispersions and a higher chiral charge of ±2. Moreover, we find that the Weyl nodes with opposite charges are located at different energies due to the absence of mirror symmetry in SrSi2, paving the way for the realization of the chiral magnetic effect. Our systematic results not only identify a much-needed robust Weyl semimetal candidate but also open the door to new topological Weyl physics that is not possible in TaAs. PMID:26787914
Vicens, Quentin; Gooding, Anne R; Duarte, Luis F; Batey, Robert T
2009-01-01
The study of functional RNAs of various sizes and structures requires efficient methods for their synthesis and purification. Here, 23 group I intron variants ranging in length from 246 to 341 nucleotides -- some containing exons -- were subjected to a native purification technique previously applied only to shorter RNAs (<160 nucleotides). For the RNAs containing both exons, we adjusted the original purification protocol to allow for purification of radiolabeled molecules. The resulting RNAs were used in folding assays on native gel electrophoresis and in self-splicing assays. The intron-only RNAs were subjected to the regular native purification scheme, assayed for folding and employed in crystallization screens. All RNAs that contained a 3' overhang of one nucleotide were efficiently cleaved off from the support and were at least 90% pure after the non-denaturing purification. A representative subset of these RNAs was shown to be folded and self-splicing after purification. Additionally, crystals were grown for a 286 nucleotide long variant of the Clostridium botulinum intron. These results demonstrate the suitability of the native affinity purification method for the preparation of group I introns. We hope these findings will stimulate a broader application of this strategy to the preparation of other large RNA molecules. PMID:19710925
Coulomb interaction effect in tilted Weyl fermion in two dimensions
NASA Astrophysics Data System (ADS)
Isobe, Hiroki; Nagaosa, Naoto
Weyl fermions with tilted linear dispersions characterized by several different velocities appear in some systems including the quasi-two-dimensional organic semiconductor α-(BEDT-TTF)2I3 and three-dimensional WTe2. The Coulomb interaction between electrons modifies the velocities in an essential way in the low energy limit, where the logarithmic corrections dominate. Taking into account the coupling to both the transverse and longitudinal electromagnetic fields, we derive the renormalization group equations for the velocities of the tilted Weyl fermions in two dimensions, and found that they increase as the energy decreases and eventually hit the velocity of light c to result in the Cherenkov radiation. Especially, the system restores the isotropic Weyl cone even when the bare Weyl cone is strongly tilted and the velocity of electrons becomes negative in certain directions.
Quantum Transport of Disordered Weyl Semimetals at the Nodal Point
NASA Astrophysics Data System (ADS)
Sbierski, Björn; Pohl, Gregor; Bergholtz, Emil J.; Brouwer, Piet W.
2014-07-01
Weyl semimetals are paradigmatic topological gapless phases in three dimensions. We here address the effect of disorder on charge transport in Weyl semimetals. For a single Weyl node with energy at the degeneracy point and without interactions, theory predicts the existence of a critical disorder strength beyond which the density of states takes on a nonzero value. Predictions for the conductivity are divergent, however. In this work, we present a numerical study of transport properties for a disordered Weyl cone at zero energy. For weak disorder, our results are consistent with a renormalization group flow towards an attractive pseudoballistic fixed point with zero conductivity and a scale-independent conductance; for stronger disorder, diffusive behavior is reached. We identify the Fano factor as a signature that discriminates between these two regimes.
Quantum transport of disordered Weyl semimetals at the nodal point.
Sbierski, Björn; Pohl, Gregor; Bergholtz, Emil J; Brouwer, Piet W
2014-07-11
Weyl semimetals are paradigmatic topological gapless phases in three dimensions. We here address the effect of disorder on charge transport in Weyl semimetals. For a single Weyl node with energy at the degeneracy point and without interactions, theory predicts the existence of a critical disorder strength beyond which the density of states takes on a nonzero value. Predictions for the conductivity are divergent, however. In this work, we present a numerical study of transport properties for a disordered Weyl cone at zero energy. For weak disorder, our results are consistent with a renormalization group flow towards an attractive pseudoballistic fixed point with zero conductivity and a scale-independent conductance; for stronger disorder, diffusive behavior is reached. We identify the Fano factor as a signature that discriminates between these two regimes. PMID:25062216
Discretized Weyl-orbit functions: modified multiplication and Galois symmetry
NASA Astrophysics Data System (ADS)
Hrivnák, J.; Walton, M. A.
2015-05-01
We note a remarkable similarity between the discretized Weyl-orbit functions and affine modular data associated with Wess-Zumino-Novikov-Witten (WZNW) conformal field theories. Known properties of the modular data are exploited here to uncover analogous results for the discretized orbit functions. We show that the product of orbit functions is modified in analogy with the truncation of tensor products known as affine fusion, governing the interactions in WZNW models. A Galois symmetry, like that of affine modular data, is also described for the discretized orbit functions.
STM studies of Weyl semimetals
NASA Astrophysics Data System (ADS)
Inoue, Hiroyuki; Gyenis, Andras; Oh, Seong Woo; Li, Jian; Wang, Zhi Jun; Bernevig, Andrei; Ni, Ni; Yazdani, Ali
Weyl semimetal exhibits a new gapless topological phase, which is characterized by an even number of band touching points of two non-degenerate bands in the bulk, called Weyl nodes. The surfaces of these compounds are expected to harbor topologically protected surface states with disconnected Fermi surfaces, called Fermi arcs, which connect surface projections of the Weyl nodes with opposing Chern numbers. Among the theoretically predicted Weyl semimetals, there have been several experimental reports on the presence of Fermi arcs in inversion-symmetry-broken monoarsenides, such as TaAs. In this talk, we will present atomic-scale imaging and spectroscopic mapping of the electronic properties of TaAs and other Weyl semimetal candidates. Such measurements have the potential to directly visualize the Fermi arc surface states of these compounds and to probe their properties. This work is supported by ARO and NSF.
On the Weyl curvature hypothesis
Stoica, Ovidiu Cristinel
2013-11-15
The Weyl curvature hypothesis of Penrose attempts to explain the high homogeneity and isotropy, and the very low entropy of the early universe, by conjecturing the vanishing of the Weyl tensor at the Big-Bang singularity. In previous papers it has been proposed an equivalent form of Einstein’s equation, which extends it and remains valid at an important class of singularities (including in particular the Schwarzschild, FLRW, and isotropic singularities). Here it is shown that if the Big-Bang singularity is from this class, it also satisfies the Weyl curvature hypothesis. As an application, we study a very general example of cosmological models, which generalizes the FLRW model by dropping the isotropy and homogeneity constraints. This model also generalizes isotropic singularities, and a class of singularities occurring in Bianchi cosmologies. We show that the Big-Bang singularity of this model is of the type under consideration, and satisfies therefore the Weyl curvature hypothesis. -- Highlights: •The singularities we introduce are described by finite geometric/physical objects. •Our singularities have smooth Riemann and Weyl curvatures. •We show they satisfy Penrose’s Weyl curvature hypothesis (Weyl=0 at singularities). •Examples: FLRW, isotropic singularities, an extension of Schwarzschild’s metric. •Example: a large class of singularities which may be anisotropic and inhomogeneous.
High affinity group III mGluRs regulate mossy fiber input to CA3 interneurons
Cosgrove, Kathleen E.; Meriney, Stephen D.; Barrionuevo, Germán
2010-01-01
Stratum lacunosum-moleculare interneurons (L-Mi) in hippocampal area CA3 target the apical dendrite of pyramidal cells providing feedforward inhibition. Here we report that selective activation of group III metabotropic glutamate receptors (mGluRs) 4/8 with L-(+)-2-amino-4-phosphnobytyric acid (L-AP4; 10 μM) decreased the probability of glutamate release from the mossy fiber (MF) terminals synapsing onto L-Mi. Consistent with this interpretation, application of L-AP4 in the presence of 3 mM strontium decreased the frequency of asynchronous MF EPSCs in L-Mi. Furthermore, the dose response curve showed that L-AP4 at 400 μM produced no further decrease in MF EPSC amplitude compared to 20 μM L-AP4, indicating the lack of mGluRs 7 at these MF terminals. We also found that one mechanism of mGluRs 4/8-mediated inhibition of release is linked to N-type voltage gated calcium channels at MF terminals. Application of the group III mGluR antagonist MSOP (100 μM) demonstrated that mGluRs 4/8 are neither tonically active nor activated by low and moderate frequencies of activity. However, trains of stimuli to the MF at 20 and 40Hz delivered during the application of MSOP revealed a relief of inhibition of transmitter release and an increase in the overall probability of action potential firing in the postsynaptic L-Mi. Interestingly, the time to first action potential was significantly shorter in the presence of MSOP, indicating that mGluR 4/8 activation delays L-Mi firing in response to MF activity. Taken together, our data demonstrate that the timing and probability of action potentials in L-Mi evoked by MF synaptic input is regulated by the activation of presynaptic high affinity group III mGluRs. PMID:20824730
NASA Astrophysics Data System (ADS)
Kikuchi, K.; Nagahama, H.
2013-12-01
A method to analyze self-affinities is introduced and applied to the large scale fold geometries of Quaternary and Tertiary sediments in the inner belt of the Northeast Honshu Arc, Japan (Kikuchi et al. 2013). Based on this analysis, their geometries are self-affine and can be differently scaled in different directions. They recognize the self-affinities for the amplitude and the wavelength of folds and a crossover from local to global altitude (vertical) variation of the geometries of folds in the Northeast Honshu Arc. Moreover, they discuss self-affinity for the crustal deformation is related to the b-value in Gutenberg-Richter's law, the fractal dimension and the uniformity of the crustal fragmentation. Softening behaviour can lead to localisation of fold packets in layered materials and a progression to chaos with fractal geometries (Hunt and Wadee, 1991). Why do fractal geometries exist and what is the control on the fractal dimension that is responsible for temperature and strain-rate dependence?(Ord and Hobbs, 2011). Shimamoto (1974) examined the conditions of similarity for geometrically similar systems of inhomogeneous viscous Newtonian fluids under similar boundary conditions, making use of the method of dimensional analysis (Buckingham's Pi-theorem). Then, based on the completely similarity, he vividly derived a relationship between the wavelength of fold and initial thickness of folded layer. Buckingham's Pi-theorem is sufficient to the first problems of fold systems. But the complete similarity can not give us the self-affinities of folds. A general renormalization-group argument is proposed to the applicability of the incomplete self-similarity theory (Barenblatt, 1979). So in this paper, based on the general renormalization-group argument, we derive the self-affinities for the amplitude and the wavelength of folds. Keywords: Fold, Self-Affinities, Dimensional Analysis, Pi-theorem, Incomplete self-similarity R e f e r e n c e s Barenblatt, G.I. (1979
Nonassociative Weyl star products
NASA Astrophysics Data System (ADS)
Kupriyanov, V. G.; Vassilevich, D. V.
2015-09-01
Deformation quantization is a formal deformation of the algebra of smooth functions on some manifold. In the classical setting, the Poisson bracket serves as an initial conditions, while the associativity allows to proceed to higher orders. Some applications to string theory require deformation in the direction of a quasi-Poisson bracket (that does not satisfy the Jacobi identity). This initial condition is incompatible with associativity, it is quite unclear which restrictions can be imposed on the deformation. We show that for any quasi-Poisson bracket the deformation quantization exists and is essentially unique if one requires (weak) hermiticity and the Weyl condition. We also propose an iterative procedure that allows one to compute the star product up to any desired order.
Hernandez Armada, Daniel; Santos, Jobette T; Richards, Michele R; Cairo, Christopher W
2015-11-19
A variety of applications in glycobiology exploit affinity chromatography through the immobilization of glycans to a solid support. Although several strategies are known, they may provide certain advantages or disadvantages in how the sugar is attached to the affinity matrix. Additionally, the products of some methods may be hard to characterize chemically due to non-specific reactions. The lack of specificity in standard immobilization reactions makes affinity chromatography with expensive oligosaccharides challenging. As a result, methods for specific and efficient immobilization of oligosaccharides remain of interest. Herein, we present a method for the immobilization of saccharides using N'-glycosylsulfonohydrazide (GSH) carbohydrate donors. We have compared GSH immobilization to known strategies, including the use of divinyl sulfone (DVS) and cyanuric chloride (CC), for the generation of affinity matrices. We compared immobilization methods by determining their immobilization efficiency, based on a comparison of the mass of immobilized carbohydrate and the concentration of active binding sites (determined using lectins). Our results indicate that immobilization using GSH donors can provide comparable amounts of carbohydrate epitopes on solid support while consuming almost half of the material required for DVS immobilization. The lectin binding capacity observed for these two methods suggests that GSH immobilization is more efficient. We propose that this method of oligosaccharide immobilization will be an important tool for glycobiologists working with precious glycan samples purified from biological sources. PMID:26454791
Electromagnetic response of Weyl semimetals.
Vazifeh, M M; Franz, M
2013-07-12
It has been suggested recently, based on subtle field-theoretical considerations, that the electromagnetic response of Weyl semimetals and the closely related Weyl insulators can be characterized by an axion term θE·B with space and time dependent axion angle θ(r,t). Here we construct a minimal lattice model of the Weyl medium and study its electromagnetic response by a combination of analytical and numerical techniques. We confirm the existence of the anomalous Hall effect expected on the basis of the field theory treatment. We find, contrary to the latter, that chiral magnetic effect (that is, ground state charge current induced by the applied magnetic field) is absent in both the semimetal and the insulator phase. We elucidate the reasons for this discrepancy. PMID:23889433
Weyl's Lagrangian in teleparallel form
Burnett, James; Vassiliev, Dmitri
2009-10-15
The Weyl Lagrangian is the massless Dirac Lagrangian. The dynamical variable in the Weyl Lagrangian is a spinor field. We provide a mathematically equivalent representation in terms of a different dynamical variable - the coframe (an orthonormal tetrad of covector fields). We show that when written in terms of this dynamical variable, the Weyl Lagrangian becomes remarkably simple: it is the wedge product of axial torsion of the teleparallel connection with a teleparallel lightlike element of the coframe. We also examine the issues of U(1)-invariance and conformal invariance. Examination of the latter motivates us to introduce a positive scalar field (equivalent to a density) as an additional dynamical variable; this makes conformal invariance self-evident.
Quantum Weyl invariance and cosmology
NASA Astrophysics Data System (ADS)
Dabholkar, Atish
2016-09-01
Equations for cosmological evolution are formulated in a Weyl invariant formalism to take into account possible Weyl anomalies. Near two dimensions, the renormalized cosmological term leads to a nonlocal energy-momentum tensor and a slowly decaying vacuum energy. A natural generalization to four dimensions implies a quantum modification of Einstein field equations at long distances. It offers a new perspective on time-dependence of couplings and naturalness with potentially far-reaching consequences for the cosmological constant problem, inflation, and dark energy.
Star product and contact Weyl manifold
NASA Astrophysics Data System (ADS)
Yoshioka, Akira
2016-09-01
Contact algebra is introduced, which is a Lie algebra given as a one-dimesional exrention of a Weyl algebra. A contact Lie algebra bundle called a contact Weyl manifold is considered over a symplectic manifold which contains a Weyl manifold as a subbundle. A relationship is discussed between deformation quantization on s symplectic manifold and a Weyl manifold over the symplectic manifold. The contact Weyl manifold has a canonical connection which gives rise the relation, and is regarded as an extension of Fedosov connection.
Anomalous Hall effect in Weyl superconductors
NASA Astrophysics Data System (ADS)
Bednik, G.; Zyuzin, A. A.; Burkov, A. A.
2016-08-01
We present a theory of the anomalous Hall effect in a topological Weyl superconductor with broken time reversal symmetry. Specifically, we consider a ferromagnetic Weyl metal with two Weyl nodes of opposite chirality near the Fermi energy. In the presence of inversion symmetry, such a metal experiences a weak-coupling Bardeen–Cooper–Schrieffer instability, with pairing of parity-related eigenstates. Due to the nonzero topological charge, carried by the Weyl nodes, such a superconductor is necessarily topologically nontrivial, with Majorana surface states coexisting with the Fermi arcs of the normal Weyl metal. We demonstrate that, surprisingly, the anomalous Hall conductivity of such a superconducting Weyl metal coincides with that of a nonsuperconducting one, under certain conditions, in spite of the nonconservation of charge in a superconductor. We relate this to the existence of an extra (nearly) conserved quantity in a Weyl metal, the chiral charge.
The Weyl Definition of Redshifts
ERIC Educational Resources Information Center
Harvey, Alex
2012-01-01
In 1923, Weyl published a (not widely known) protocol for the calculation of redshifts. It is completely independent of the origin of the shift and treats it as a pure Doppler shift. The method is comprehensive and depends solely on the relation between the world lines of source and observer. It has the merit of simplicity of statement and…
Photonic Weyl degeneracies in magnetized plasma
Gao, Wenlong; Yang, Biao; Lawrence, Mark; Fang, Fengzhou; Béri, Benjamin; Zhang, Shuang
2016-01-01
Weyl particles are elusive relativistic fermionic particles with vanishing mass. While not having been found as an elementary particle, they are found to emerge in solid-state materials where three-dimensional bands develop a topologically protected point-like crossing, a so-called Weyl point. Photonic Weyl points have been recently realised in three-dimensional photonic crystals with complex structures. Here we report the presence of a novel type of plasmonic Weyl points in a naturally existing medium—magnetized plasma, in which Weyl points arise as crossings between purely longitudinal plasma modes and transverse helical propagating modes. These photonic Weyl points are right at the critical transition between a Weyl point with the traditional closed finite equifrequency surfaces and the newly proposed ‘type II' Weyl points with open equifrequency surfaces. Striking observable features of plasmon Weyl points include a half k-plane chirality manifested in electromagnetic reflection. Our study introduces Weyl physics into homogeneous photonic media, which could pave way for realizing new topological photonic devices. PMID:27506514
Photonic Weyl degeneracies in magnetized plasma.
Gao, Wenlong; Yang, Biao; Lawrence, Mark; Fang, Fengzhou; Béri, Benjamin; Zhang, Shuang
2016-01-01
Weyl particles are elusive relativistic fermionic particles with vanishing mass. While not having been found as an elementary particle, they are found to emerge in solid-state materials where three-dimensional bands develop a topologically protected point-like crossing, a so-called Weyl point. Photonic Weyl points have been recently realised in three-dimensional photonic crystals with complex structures. Here we report the presence of a novel type of plasmonic Weyl points in a naturally existing medium-magnetized plasma, in which Weyl points arise as crossings between purely longitudinal plasma modes and transverse helical propagating modes. These photonic Weyl points are right at the critical transition between a Weyl point with the traditional closed finite equifrequency surfaces and the newly proposed 'type II' Weyl points with open equifrequency surfaces. Striking observable features of plasmon Weyl points include a half k-plane chirality manifested in electromagnetic reflection. Our study introduces Weyl physics into homogeneous photonic media, which could pave way for realizing new topological photonic devices. PMID:27506514
Photonic Weyl degeneracies in magnetized plasma
NASA Astrophysics Data System (ADS)
Gao, Wenlong; Yang, Biao; Lawrence, Mark; Fang, Fengzhou; Béri, Benjamin; Zhang, Shuang
2016-08-01
Weyl particles are elusive relativistic fermionic particles with vanishing mass. While not having been found as an elementary particle, they are found to emerge in solid-state materials where three-dimensional bands develop a topologically protected point-like crossing, a so-called Weyl point. Photonic Weyl points have been recently realised in three-dimensional photonic crystals with complex structures. Here we report the presence of a novel type of plasmonic Weyl points in a naturally existing medium--magnetized plasma, in which Weyl points arise as crossings between purely longitudinal plasma modes and transverse helical propagating modes. These photonic Weyl points are right at the critical transition between a Weyl point with the traditional closed finite equifrequency surfaces and the newly proposed `type II' Weyl points with open equifrequency surfaces. Striking observable features of plasmon Weyl points include a half k-plane chirality manifested in electromagnetic reflection. Our study introduces Weyl physics into homogeneous photonic media, which could pave way for realizing new topological photonic devices.
Chiral anomaly and transport in Weyl metals
NASA Astrophysics Data System (ADS)
Burkov, A. A.
2015-03-01
We present an overview of our recent work on transport phenomena in Weyl metals, which may be connected to their nontrivial topological properties, particularly to chiral anomaly. We argue that there are two basic phenomena, which are related to chiral anomaly in Weyl metals: anomalous Hall effect (AHE) and chiral magnetic effect (CME). While AHE is in principle present in any ferromagnetic metal, we demonstrate that a magnetic Weyl metal is distinguished from an ordinary ferromagnetic metal by the absence of the extrinsic and the Fermi surface part of the intrinsic contributions to the AHE, as long as the Fermi energy is sufficiently close to the Weyl nodes. The AHE in a Weyl metal is thus shown to be a purely intrinsic, universal property, fully determined by the location of the Weyl nodes in the first Brillouin zone. In other words, a ferromagnetic Weyl metal may be thought of as the only example of a ferromagnetic metal with a purely intrinsic AHE. We further develop a fully microscopic theory of diffusive magnetotransport in Weyl metals. We derive coupled diffusion equations for the total and axial (i.e. node-antisymmetric) charge densities and show that chiral anomaly manifests as a magnetic-field-induced coupling between them. We demonstrate that an experimentally-observable consequence of CME in magnetotransport in Weyl metals is a quadratic negative magnetoresistance, which will dominate all other contributions to magnetoresistance under certain conditions and may be regarded as a smoking-gun transport characteristic, unique to Weyl metals.
Chiral anomaly and transport in Weyl metals.
Burkov, A A
2015-03-25
We present an overview of our recent work on transport phenomena in Weyl metals, which may be connected to their nontrivial topological properties, particularly to chiral anomaly. We argue that there are two basic phenomena, which are related to chiral anomaly in Weyl metals: anomalous Hall effect (AHE) and chiral magnetic effect (CME). While AHE is in principle present in any ferromagnetic metal, we demonstrate that a magnetic Weyl metal is distinguished from an ordinary ferromagnetic metal by the absence of the extrinsic and the Fermi surface part of the intrinsic contributions to the AHE, as long as the Fermi energy is sufficiently close to the Weyl nodes. The AHE in a Weyl metal is thus shown to be a purely intrinsic, universal property, fully determined by the location of the Weyl nodes in the first Brillouin zone. In other words, a ferromagnetic Weyl metal may be thought of as the only example of a ferromagnetic metal with a purely intrinsic AHE. We further develop a fully microscopic theory of diffusive magnetotransport in Weyl metals. We derive coupled diffusion equations for the total and axial (i.e. node-antisymmetric) charge densities and show that chiral anomaly manifests as a magnetic-field-induced coupling between them. We demonstrate that an experimentally-observable consequence of CME in magnetotransport in Weyl metals is a quadratic negative magnetoresistance, which will dominate all other contributions to magnetoresistance under certain conditions and may be regarded as a smoking-gun transport characteristic, unique to Weyl metals. PMID:25712419
Cambrian origins and affinities of an enigmatic fossil group of arthropods.
Vaccari, N E; Edgecombe, G D; Escudero, C
2004-07-29
Euthycarcinoids are one of the most enigmatic arthropod groups, having been assigned to nearly all major clades of Arthropoda. Recent work has endorsed closest relationships with crustaceans or a myriapod-hexapod assemblage, a basal position in the Euarthropoda, or a placement in the Hexapoda or hexapod stem group. Euthycarcinoids are known from 13 species ranging in age from Late Ordovician or Early Silurian to Middle Triassic, all in freshwater or brackish water environments. Here we describe a euthycarcinoid from marine strata in Argentina dating from the latest Cambrian period, extending the group's record back as much as 50 million years. Despite its antiquity and marine occurrence, the Cambrian species demonstrates that morphological details were conserved in the transition to fresh water. Trackways in the same unit as the euthycarcinoid strengthen arguments that similar traces of subaerial origin from Cambro-Ordovician rocks were made by euthycarcinoids. Large mandibles in euthycarcinoids are confirmed by the Cambrian species. A morphology-based phylogeny resolves euthycarcinoids as stem-group Mandibulata, sister to the Myriapoda and Crustacea plus Hexapoda. PMID:15282604
The Hermann Weyl Prize - Laudatio for Guilio Chiribella
NASA Astrophysics Data System (ADS)
del Olmo, M. A.
2011-03-01
The Hermann Weyl Prize was created in 2000 by the Standing Committee of the International Group Theory Colloquium. The purpose of the Weyl Prize is to provide recognition for young scientists (younger than 35) who have performed original work of significant scientific quality in the area of understanding physics through symmetries. The Hermann Weyl Prize consists of a certificate citing the accomplishments of the recipient, prize money of $500 and an allowance towards the attendance of the bi-annual International Group Theory Colloquium at which the award is presented. The previous winners of the award were: Edward Frenkel (2002), Nikita A Nekrasov (2004), Boyko Bakalov (2006) and Mohammad M Sheikh-Jabbari (2008). The Selection Committee of the Weyl Prize 2010 consisted of S T Ali (Concordia University), E Corrigan (Durham Univeristy), P Kulish (St Petersburg Mathematical Institute of the Russian Academy of Sciences), R Mosseri (CNRS Paris) and M A del Olmo (University of Valladolid, chairman). This committee has made the following announcement: The Weyl Prize for the year 2010 was awarded to Dr Giulio Chiribella, in recognition of his pioneering work on the application of group theoretical methods in Quantum Information Theory. In particular, for providing a general solution to the problem of optimal estimation of symmertry transformations based on the notion of quantum entanglement between representation and multiplicity spaces, for the derivation of optimal protocols for the alignment of quantum reference frames, for the characterization of extreme quantum measurements in finite dimensions, for the proof of equivalence between asymptotic cloning and state estimation and for the proof of the optimality of measure-and-reprepare for quantum learning of unitary transformations. The Laudatio of Guilio Chiribella, delivered by M A del Olmo, is included in the PDF.
Spacetimes with vector distortion: Inflation from generalised Weyl geometry
NASA Astrophysics Data System (ADS)
Beltrán Jiménez, Jose; Koivisto, Tomi S.
2016-05-01
Spacetime with general linear vector distortion is introduced. Thus, the torsion and the nonmetricity of the affine connection are assumed to be proportional to a vector field (and not its derivatives). The resulting two-parameter family of non-Riemannian geometries generalises the conformal Weyl geometry and some other interesting special cases. Taking into account the leading nonlinear correction to the Einstein-Hilbert action results uniquely in the one-parameter extension of the Starobinsky inflation known as the alpha-attractor. The most general quadratic curvature action introduces, in addition to the canonical vector kinetic term, novel ghost-free vector-tensor interactions.
Barrantes, R; Smouse, P E; Neel, J V; Mohrenweiser, H W; Gershowitz, H
1982-06-01
New genetic data on 40 red cell enzymes, antigenic blood groups, and serum proteins representing 42 separate loci, are reported for two Guaymi communities in Southeastern Costa Rica. These two settlements, Limoncito and Abrojo, are of recent origin, having been established by Panamanian migrants in the last 50 years. Detailed data on the provenance of these migrants permits an analysis of how these settlement patterns differ from those typical of less acculturated Amerindians from the lowlands of South America. The genetic compositions of these two communities are compared with those of previous Panamanian Guaymi samples, and several points are established: (1) One of the localities, Limoncito, contains families from both Guaymi dialect groups (eastern and western), and the allelic frequencies are intermediate between those of the dialect groups. (2) The other settlement, Abrojo, is quite similar to the western Guaymi, as expected from historical reconstruction of its antecedents. (3) In general, the degree of infratribal genetic diversity is less than that found in lowland South American tribes, and the difference may be due to a diffuse settlement pattern among the Guaymi. (4) The Guaymi are also compared genetically with other tribes in low Central America and northern South America, and appear to be similar to their immediate Chibcha neighbors to the east and west. The implications of a pair of "private polymorphisms" are discussed in the context of the time of dialectic and tribal divergence in this zone. PMID:6180642
Hyperbolic Weyl Point in Reciprocal Chiral Metamaterials
NASA Astrophysics Data System (ADS)
Xiao, Meng; Lin, Qian; Fan, Shanhui
2016-07-01
We report the existence of Weyl points in a class of noncentral symmetric metamaterials, which has time reversal symmetry, but does not have inversion symmetry due to chiral coupling between electric and magnetic fields. This class of metamaterial exhibits either type-I or type-II Weyl points depending on its nonlocal response. We also provide a physical realization of such metamaterial consisting of an array of metal wires in the shape of elliptical helices which exhibits type-II Weyl points.
Extending the ADM formalism to Weyl geometry
Barreto, A. B.; Almeida, T. S.; Romero, C.
2015-03-26
In order to treat quantum cosmology in the framework of Weyl spacetimes we take the first step of extending the Arnowitt-Deser-Misner formalism to Weyl geometry. We then obtain an expression of the curvature tensor in terms of spatial quantities by splitting spacetime in (3+l)-dimensional form. We next write the Lagrangian of the gravitation field based in Weyl-type gravity theory. We extend the general relativistic formalism in such a way that it can be applied to investigate the quantum cosmology of models whose spacetimes are endowed with a Weyl geometrical structure.
Observation of Weyl fermions in condensed matter
NASA Astrophysics Data System (ADS)
Ding, Hong
In 1929, a German mathematician and physicist Hermann Weyl proposed that a massless solution of the Dirac equation represents a pair of new type of particles, the so-called Weyl fermions. However, their existence in particle physics remains elusive after more than eight decades, e.g., neutrino has been regarded as a Weyl fermion in the Standard Model until it was found to have mass. Recently, significant advances in topological materials have provided an alternative way to realize Weyl fermions in condensed matter as an emergent phenomenon. Weyl semimetals are predicted as a class of topological materials that can be regarded as three-dimensional analogs of graphene breaking time reversal or inversion symmetry. Electrons in a Weyl semimetal behave exactly as Weyl fermions, which have many exotic properties, such as chiral anomaly, magnetic monopoles in the crystal momentum space, and open Fermi arcs on the surface. In this talk I will report our experimental discovery of a Weyl semimetal in TaAs by observing Fermi arcs with a characteristic spin texture in the surface states and Weyl nodes in the bulk states using angle-resolved photoemission spectroscopy.
Topological photonic crystal with ideal Weyl points
NASA Astrophysics Data System (ADS)
Wang, Luyang; Jian, Shao-Kai; Yao, Hong
Weyl points in three-dimensional photonic crystals behave as monopoles of Berry flux in momentum space. Here, based on symmetry analysis, we show that a minimal number of symmetry-related Weyl points can be realized in time-reversal invariant photonic crystals. We propose to realize these ``ideal'' Weyl points in modified double-gyroid photonic crystals, which is confirmed by our first-principle photonic band-structure calculations. Photonic crystals with ideal Weyl points are qualitatively advantageous in applications such as angular and frequency selectivity, broadband invisibility cloaking, and broadband 3D-imaging.
Topological photonic crystal with equifrequency Weyl points
NASA Astrophysics Data System (ADS)
Wang, Luyang; Jian, Shao-Kai; Yao, Hong
2016-06-01
Weyl points in three-dimensional photonic crystals behave as monopoles of Berry flux in momentum space. Here, based on general symmetry analysis, we show that a minimal number of four symmetry-related (consequently equifrequency) Weyl points can be realized in time-reversal invariant photonic crystals. We further propose an experimentally feasible way to modify double-gyroid photonic crystals to realize four equifrequency Weyl points, which is explicitly confirmed by our first-principle photonic band-structure calculations. Remarkably, photonic crystals with equifrequency Weyl points are qualitatively advantageous in applications including angular selectivity, frequency selectivity, invisibility cloaking, and three-dimensional imaging.
NASA Astrophysics Data System (ADS)
Bytsenko, A. A.; Chaichian, M.
2016-06-01
In this paper we analyze the quantum homological invariants (the Poincaré polynomials of the slN link homology). In the case when the dimensions of homologies of appropriate topological spaces are precisely known, the procedure of the calculation of the Kovanov-Rozansky type homology, based on the Euler-Poincaré formula can be appreciably simplified. We express the formal character of the irreducible tensor representation of the classical groups in terms of the symmetric and spectral functions of hyperbolic geometry. On the basis of Labastida-Mariño-Ooguri-Vafa conjecture, we derive a representation of the Chern-Simons partition function in the form of an infinite product in terms of the Ruelle spectral functions (the cases of a knot, unknot, and links have been considered). We also derive an infinite-product formula for the orthogonal Chern-Simons partition functions and analyze the singularities and the symmetry properties of the infinite-product structures.
Classification of stable Dirac and Weyl semimetals with reflection and rotational symmetry
NASA Astrophysics Data System (ADS)
Gao, Zihao; Hua, Meng; Zhang, Haijun; Zhang, Xiao
2016-05-01
Three-dimensional (3D) Dirac and Weyl semimetals are novel states of quantum matter. We classify stable 3D Dirac and Weyl semimetals with reflection and rotational symmetry in the presence of time reversal symmetry and spin-orbit coupling, which belong to seventeen different point groups. They have two classes of reflection symmetry, with the mirror plane parallel and perpendicular to rotation axis. In both cases two types of Dirac points, existing through accidental band crossing (ABC) or at a time reversal invariant momentum (TBC), are determined by four different reflection symmetries. We classify those two types of Dirac points with a combination of different reflection and rotational symmetries. We further classify Dirac and Weyl line nodes to show in which types of mirror plane they can exist. Finally we discuss that Weyl line nodes and Dirac points can exist at the same time taking C4 v symmetry as an example.
Coulomb Interaction Effect in Weyl Fermions with Tilted Energy Dispersion in Two Dimensions.
Isobe, Hiroki; Nagaosa, Naoto
2016-03-18
Weyl fermions with tilted linear dispersions characterized by several different velocities appear in some systems including the quasi-two-dimensional organic semiconductor α-(BEDT-TTF)_{2}I_{3} and three-dimensional WTe_{2}. The Coulomb interaction between electrons modifies the velocities in an essential way in the low-energy limit, where the logarithmic corrections dominate. Taking into account the coupling to both the transverse and longitudinal electromagnetic fields, we derive the renormalization group equations for the velocities of the tilted Weyl fermions in two dimensions, and found that they increase as the energy decreases and eventually hit the speed of light c to result in the Cherenkov radiation. Especially, the system restores the isotropic Weyl cone even when the bare Weyl cone is strongly tilted and the velocity of electrons becomes negative in certain directions. PMID:27035318
Coulomb Interaction Effect in Weyl Fermions with Tilted Energy Dispersion in Two Dimensions
NASA Astrophysics Data System (ADS)
Isobe, Hiroki; Nagaosa, Naoto
2016-03-01
Weyl fermions with tilted linear dispersions characterized by several different velocities appear in some systems including the quasi-two-dimensional organic semiconductor α -(BEDT -TTF )2I3 and three-dimensional WTe2 . The Coulomb interaction between electrons modifies the velocities in an essential way in the low-energy limit, where the logarithmic corrections dominate. Taking into account the coupling to both the transverse and longitudinal electromagnetic fields, we derive the renormalization group equations for the velocities of the tilted Weyl fermions in two dimensions, and found that they increase as the energy decreases and eventually hit the speed of light c to result in the Cherenkov radiation. Especially, the system restores the isotropic Weyl cone even when the bare Weyl cone is strongly tilted and the velocity of electrons becomes negative in certain directions.
Surface plasmon polaritons in topological Weyl semimetals
NASA Astrophysics Data System (ADS)
Hofmann, Johannes; Das Sarma, Sankar
2016-06-01
We consider theoretically surface plasmon polaritons in Weyl semimetals. These materials contain pairs of band touching points—Weyl nodes—with a chiral topological charge, which induces an optical anisotropy and anomalous transport through the chiral anomaly. We show that these effects, which are not present in ordinary metals, have a direct fundamental manifestation in the surface plasmon dispersion. The retarded Weyl surface plasmon dispersion depends on the separation of the Weyl nodes in energy and momentum space. For Weyl semimetals with broken time-reversal symmetry, the distance between the nodes acts as an effective applied magnetic field in momentum space, and the Weyl surface plasmon polariton dispersion is strikingly similar to magnetoplasmons in ordinary metals. In particular, this implies the existence of nonreciprocal surface modes. In addition, we obtain the nonretarded Weyl magnetoplasmon modes, which acquire an additional longitudinal magnetic field dependence. These predicted surface plasmon results are observable manifestations of the chiral anomaly in Weyl semimetals and might have technological applications.
Geng, Song; Wu, Ding-Lu; Yang, Jing; Wei, Xi-Guang; Zhu, Jun; Zhang, Hai-Bo; Ren, Yi; Lau, Kai-Chung
2014-05-01
We have made an extensive theoretical exploration of gas-phase N-alkylamino cation affinities (NAAMCA), including amino cation affinities (AMCA) and N-dimethylamino cation affinities (NDMAMCA), of neutral main-group element hydrides of groups 15-17 and periods 2-4 in the periodic table by using the G2(+)M method. Some similarities and differences are found between NAAMCA and the corresponding alkyl cation affinities (ACA) of H(n)X. Our calculations show that the AMCA and NDMAMCA are systematically lower than the corresponding proton affinities (PA) for H(n)X. In general, there is no linear correlation between NAAMCA and PA of H(n)X. Instead, the correlations exist only within the central elements X in period 2, or periods 3-4, which is significantly different from the reasonable correlations between ACA and PA for all H(n)X. NAAMCA (H(n)X) are weaker than NAAMCA (H(n-1)X(-)) by more than 700 kJ/mol and generally stronger than ACA (H(n)X), with three exceptions: H2ONR2(+)(R = H, Me) and HFNH2(+). These new findings can be rationalized by the negative hyperconjugation and Pauli repulsion. PMID:24738576
Interpretation of the Weyl tensor
NASA Astrophysics Data System (ADS)
Hofmann, Stefan; Niedermann, Florian; Schneider, Robert
2013-09-01
According to folklore in general relativity, the Weyl tensor can be decomposed into parts corresponding to Newton-like, incoming and outgoing wavelike field components. It is shown here that this one-to-one correspondence does not hold for space-time geometries with cylindrical isometries. This is done by investigating some well-known exact solutions of Einstein’s field equations with whole-cylindrical symmetry, for which the physical interpretation is very clear, but for which the standard Weyl interpretation would give contradictory results. For planar or spherical geometries, however, the standard interpretation works for both static and dynamical space-times. It is argued that one reason for the failure in the cylindrical case is that for waves spreading in two spatial dimensions there is no local criterion to distinguish incoming and outgoing waves already at the linear level. It turns out that Thorne’s local energy notion, subject to certain qualifications, provides an efficient diagnostic tool to extract the proper physical interpretation of the space-time geometry in the case of cylindrical configurations.
Beyond Dirac and Weyl fermions: Unconventional quasiparticles in conventional crystals.
Bradlyn, Barry; Cano, Jennifer; Wang, Zhijun; Vergniory, M G; Felser, C; Cava, R J; Bernevig, B Andrei
2016-08-01
In quantum field theory, we learn that fermions come in three varieties: Majorana, Weyl, and Dirac. Here, we show that in solid-state systems this classification is incomplete, and we find several additional types of crystal symmetry-protected free fermionic excitations. We exhaustively classify linear and quadratic three-, six-, and eight-band crossings stabilized by space group symmetries in solid-state systems with spin-orbit coupling and time-reversal symmetry. Several distinct types of fermions arise, differentiated by their degeneracies at and along high-symmetry points, lines, and surfaces. Some notable consequences of these fermions are the presence of Fermi arcs in non-Weyl systems and the existence of Dirac lines. Ab initio calculations identify a number of materials that realize these exotic fermions close to the Fermi level. PMID:27445310
Spin-1 Dirac-Weyl fermions protected by bipartite symmetry
NASA Astrophysics Data System (ADS)
Lin, Zeren; Liu, Zhirong
2015-12-01
We propose that bipartite symmetry allows spin-1 Dirac-Weyl points, a generalization of the spin-1/2 Dirac points in graphene, to appear as topologically protected at the Fermi level. In this spirit, we provide methodology to construct spin-1 Dirac-Weyl points of this kind in a given 2D space group and get the classification of the known spin-1 systems in the literature. We also apply the workflow to predict two new systems, P3m1-9 and P31m-15, to possess spin-1 at K/K' in the Brillouin zone of hexagonal lattice. Their stability under various strains is investigated and compared with that of T3, an extensively studied model of ultracold atoms trapped in optical lattice with spin-1 also at K/K'.
Spin-1 Dirac-Weyl fermions protected by bipartite symmetry
Lin, Zeren; Liu, Zhirong
2015-12-07
We propose that bipartite symmetry allows spin-1 Dirac-Weyl points, a generalization of the spin-1/2 Dirac points in graphene, to appear as topologically protected at the Fermi level. In this spirit, we provide methodology to construct spin-1 Dirac-Weyl points of this kind in a given 2D space group and get the classification of the known spin-1 systems in the literature. We also apply the workflow to predict two new systems, P3m1-9 and P31m-15, to possess spin-1 at K/K′ in the Brillouin zone of hexagonal lattice. Their stability under various strains is investigated and compared with that of T{sub 3}, an extensively studied model of ultracold atoms trapped in optical lattice with spin-1 also at K/K′.
Polynomial Extensions of the Weyl C*-Algebra
NASA Astrophysics Data System (ADS)
Accardi, Luigi; Dhahri, Ameur
2015-09-01
We introduce higher order (polynomial) extensions of the unique (up to isomorphisms) nontrivial central extension of the Heisenberg algebra, which can be concretely realized as sub-Lie algebras of the polynomial algebra generated by the creation and annihilation operators in the Schrödinger representation. The simplest nontrivial of these extensions (the quadratic one) is isomorphic to the Galilei algebra, widely studied in quantum physics. By exponentiation of this representation we construct the corresponding polynomial analogue of the Weyl C*-algebra and compute the polynomial Weyl relations. From this we deduce the explicit form of the composition law of the associated nonlinear extensions of the 1-dimensional Heisenberg group. The above results are used to calculate a simple explicit form of the vacuum characteristic functions of the nonlinear field operators of the Galilei algebra, as well as of their moments. The corresponding measures turn out to be an interpolation family between Gaussian and Meixner, in particular Gamma.
ERIC Educational Resources Information Center
Jones, Jayatta D.
2012-01-01
Women Reading for Education, Affinity & Development (WREAD), a reading discussion group geared toward African American female adult-literacy students with self-defined histories of trauma, was an outgrowth of research identifying links between trauma, women's struggles with literacy, and the need to be conscious of emotional health…
Guigues, Stéphanie; Bravin, Matthieu N; Garnier, Cédric; Masion, Armand; Chevassus-Rosset, Claire; Cazevieille, Patrick; Doelsch, Emmanuel
2016-03-16
Carboxylic groups located in plant cell walls (CW) are generally considered to be the main copper binding sites in plant roots, despite the presence of other functional groups. The aim of this study was to investigate sites responsible for copper binding in root apoplasts, i.e. CW and outer surface of the plasma membrane (PM) continuum. Binding sites in root apoplasts were investigated by comparing isolated CW of a monocotyledon (Triticum aestivum L.) and dicotyledon (Solanum lycopersicum L.) crop with their respective whole roots. Copper speciation was examined by X-ray absorption (XAS) and (13)C-nuclear magnetic resonance spectroscopies while the affinity of ligands involved in copper binding was investigated by modeling copper sorption isotherms. Homogeneous speciation and binding of copper was found in wheat and tomato root apoplasts. Only Cu-N and Cu-O bonds were detected in wheat and tomato root apoplasts. Nitrogen/oxygen ligands were identified in slightly higher proportions (40-70%) than single oxygen ligands. Furthermore, low- and high-affinity binding sites contributed in an almost equivalent proportion to copper binding in root apoplasts. The high-affinity N functional groups embedded in root apoplasts participated in copper binding in the same magnitude than the low-affinity carboxylic groups. PMID:26824877
Hyperbolic Weyl Point in Reciprocal Chiral Metamaterials.
Xiao, Meng; Lin, Qian; Fan, Shanhui
2016-07-29
We report the existence of Weyl points in a class of noncentral symmetric metamaterials, which has time reversal symmetry, but does not have inversion symmetry due to chiral coupling between electric and magnetic fields. This class of metamaterial exhibits either type-I or type-II Weyl points depending on its nonlocal response. We also provide a physical realization of such metamaterial consisting of an array of metal wires in the shape of elliptical helices which exhibits type-II Weyl points. PMID:27517792
Arimitsu, Hideyuki; Sasaki, Keiko; Kojima, Hiroe; Yanaka, Tadashi; Tsuji, Takao
2013-01-01
Here we describe a simple affinity purification method for Shiga toxin 2e (Stx2e), a major causative factor of edema disease in swine. Escherichia coli strain MV1184 transformed with the expression plasmid pBSK-Stx2e produced Stx2e when cultivated in CAYE broth containing lincomycin. Stx2e bound to commercial D-galactose gel, containing α-D-galactose immobilized on agarose resin via a divinyl sulfone linker, and was eluted with phosphate-buffered saline containing 4.5 M MgCl2. A small amount of Stx2e bound to another commercial α-galactose-immobilized agarose resin, but not to β-galactose-immobilized resin. In addition, Stx2e bound to thiophilic adsorbent resin containing β-mercaptoethanol immobilized on agarose resin via a divinyl sulfone, and was purified in the same manner as from D-galactose gel, but the Stx2e sample contained some contamination. These results indicate that Stx2e bound to D-galactose gel mainly through the divinyl sulfone group on the resin and to a lesser extent through α-D-galactose. With these methods, the yields of Stx2e and attenuated mutant Stx2e (mStx2e) from 1 L of culture were approximately 36 mg and 27.7 mg, respectively, and the binding capacity of the D-galactose gel and thiophilic adsorbent resin for Stx2e was at least 20 mg per 1 ml of resin. In addition, using chimeric toxins with prototype Stx2 which did not bind to thiophilic adsorbent resin and some types of mutant Stx2e and Stx2 which contained inserted mutations in the B subunits, we found that, at the least, asparagine (amino acid 17 of the B subunits) was associated with Stx2e binding to the divinyl sulfone group. The mStx2e that was isolated exhibited vaccine effects in ICR mice, indicating that these methods are beneficial for large-scale preparation of Stx2e toxoid, which protects swine from edema disease. PMID:24340102
Weyl corrections to holographic conductivity
Ritz, Adam; Ward, John
2009-03-15
For conformal field theories which admit a dual gravitational description in anti-de Sitter space, electrical transport properties, such as conductivity and charge diffusion, are determined by the dynamics of a U(1) gauge field in the bulk and thus obey universality relations at the classical level due to the uniqueness of the Maxwell action. We analyze corrections to these transport parameters due to higher-dimension operators in the bulk action, beyond the leading Maxwell term, of which the most significant involves a coupling to the bulk Weyl tensor. We show that the ensuing corrections to conductivity and the diffusion constant break the universal relation with the U(1) central charge observed at leading order, but are nonetheless subject to interesting bounds associated with causality in the boundary conformal field theory.
Transversal magnetoresistance in Weyl semimetals
NASA Astrophysics Data System (ADS)
Klier, J.; Gornyi, I. V.; Mirlin, A. D.
2015-11-01
We explore theoretically the magnetoresistivity of three-dimensional Weyl and Dirac semimetals in transversal magnetic fields within two alternative models of disorder: (i) short-range impurities and (ii) charged (Coulomb) impurities. Impurity scattering is treated using the self-consistent Born approximation. We find that an unusual broadening of Landau levels leads to a variety of regimes of the resistivity scaling in the temperature-magnetic field plane. In particular, the magnetoresistance is nonmonotonous for the white-noise disorder model. For H →0 the magnetoresistance for short-range impurities vanishes in a nonanalytic way as H1 /3. In the limits of strongest magnetic fields H , the magnetoresistivity vanishes as 1 /H for pointlike impurities, while it is linear and positive in the model with Coulomb impurities.
Conventionalism and integrable Weyl geometry
NASA Astrophysics Data System (ADS)
Pucheu, M. L.
2015-03-01
Since the appearance of Einstein's general relativity, gravitation has been associated to the space-time curvature. This theory introduced a geometrodynamic language which became a convenient tool to predict matter behaviour. However, the properties of space-time itself cannot be measurable by experiments. Taking Poincaré idea that the geometry of space-time is merely a convention, we show that the general theory of relativity can be completely reformulated in a more general setting, a generalization of Riemannian geometry, namely, the Weyl integrable geometry. The choice of this new mathematical language implies, among other things, that the path of particles and light rays should now correspond to Weylian geodesies. Such modification in the dynamic of bodies brings a new perception of physical phenomena that we will explore.
Quantum Materials: Weyl fermions go into orbit
NASA Astrophysics Data System (ADS)
Dai, Xi
2016-08-01
Due to their chirality, the massless fermions inside Weyl semimetals can take unusual paths that are governed by chiral dynamics, potentially providing a direct method to explore their topological nature.
Weyl's Abandonment of Unified Field Theory
NASA Astrophysics Data System (ADS)
Sieroka, Norman
2015-01-01
In 1918, Hermann Weyl proposed a generalisation of Riemannian geometry, in order to unify general relativity and electrodynamics. This paper investigates the physical, mathematical and philosophical reasons for his subsequent abandonment of any such attempt towards a unified field theory.
Five-dimensional generalization of the topological Weyl semimetal
NASA Astrophysics Data System (ADS)
Lian, Biao; Zhang, Shou-Cheng
2016-07-01
We generalize the concept of three-dimensional topological Weyl semimetals to a class of five dimensional (5D) gapless solids, where Weyl points are generalized to Weyl surfaces which are two-dimensional closed manifolds in the momentum space. Each Weyl surface is characterized by a U (1 ) second Chern number C2 defined on a four-dimensional manifold enclosing the Weyl surface, which is equal to its topological linking number with other Weyl surfaces in 5D. In analogy to the Weyl semimetals, the surface states of the 5D metal take the form of topologically protected Weyl fermion arcs, which connect the projections of the bulk Weyl surfaces. The further generalization of topological metals in 2 n +1 dimensions carrying the n th Chern number Cn is also discussed.
Metric reconstruction from Weyl scalars
NASA Astrophysics Data System (ADS)
Whiting, Bernard F.; Price, Larry R.
2005-08-01
The Kerr geometry has remained an elusive world in which to explore physics and delve into the more esoteric implications of general relativity. Following the discovery, by Kerr in 1963, of the metric for a rotating black hole, the most major advance has been an understanding of its Weyl curvature perturbations based on Teukolsky's discovery of separable wave equations some ten years later. In the current research climate, where experiments across the globe are preparing for the first detection of gravitational waves, a more complete understanding than concerns just the Weyl curvature is now called for. To understand precisely how comparatively small masses move in response to the gravitational waves they emit, a formalism has been developed based on a description of the whole spacetime metric perturbation in the neighbourhood of the emission region. Presently, such a description is not available for the Kerr geometry. While there does exist a prescription for obtaining metric perturbations once curvature perturbations are known, it has become apparent that there are gaps in that formalism which are still waiting to be filled. The most serious gaps include gauge inflexibility, the inability to include sources—which are essential when the emitting masses are considered—and the failure to describe the ell = 0 and 1 perturbation properties. Among these latter properties of the perturbed spacetime, arising from a point mass in orbit, are the perturbed mass and axial component of angular momentum, as well as the very elusive Carter constant for non-axial angular momentum. A status report is given on recent work which begins to repair these deficiencies in our current incomplete description of Kerr metric perturbations.
Thermodynamics and entanglement entropy with Weyl corrections
NASA Astrophysics Data System (ADS)
Dey, Anshuman; Mahapatra, Subhash; Sarkar, Tapobrata
2016-07-01
We consider charged black holes in four-dimensional anti-de Sitter space, in the presence of a Weyl correction. We obtain the solution including the effect of backreaction, perturbatively up to first order in the Weyl coupling, and study its thermodynamic properties. This is complemented by a calculation of the holographic entanglement entropy of the boundary theory. The consistency of results obtained from both computations is established.
Linear dependencies in Weyl-Heisenberg orbits
NASA Astrophysics Data System (ADS)
Dang, Hoan Bui; Blanchfield, Kate; Bengtsson, Ingemar; Appleby, D. M.
2013-11-01
Five years ago, Lane Hughston showed that some of the symmetric informationally complete positive operator valued measures (SICs) in dimension 3 coincide with the Hesse configuration (a structure well known to algebraic geometers, which arises from the torsion points of a certain elliptic curve). This connection with elliptic curves is signalled by the presence of linear dependencies among the SIC vectors. Here we look for analogous connections between SICs and algebraic geometry by performing computer searches for linear dependencies in higher dimensional SICs. We prove that linear dependencies will always emerge in Weyl-Heisenberg orbits when the fiducial vector lies in a certain subspace of an order 3 unitary matrix. This includes SICs when the dimension is divisible by 3 or equal to 8 mod 9. We examine the linear dependencies in dimension 6 in detail and show that smaller dimensional SICs are contained within this structure, potentially impacting the SIC existence problem. We extend our results to look for linear dependencies in orbits when the fiducial vector lies in an eigenspace of other elements of the Clifford group that are not order 3. Finally, we align our work with recent studies on representations of the Clifford group.
Critical exponents at the unconventional disorder-driven transition in a Weyl semimetal
NASA Astrophysics Data System (ADS)
Syzranov, S. V.; Ostrovsky, P. M.; Gurarie, V.; Radzihovsky, L.
2016-04-01
Disordered noninteracting systems in sufficiently high dimensions have been predicted to display a non-Anderson disorder-driven transition that manifests itself in the critical behavior of the density of states and other physical observables. Recently, the critical properties of this transition have been extensively studied for the specific case of Weyl semimetals by means of numerical and renormalisation-group approaches. Despite this, the values of the critical exponents at such a transition in a Weyl semimetal are currently under debate. We present an independent calculation of the critical exponents using a two-loop renormalization-group approach for Weyl fermions in 2 -ɛ dimensions and resolve controversies currently existing in the literature.
NASA Astrophysics Data System (ADS)
Jho, Yong-Soo; Kim, Ki-Seok
2013-05-01
We predict that long-range interactions give rise to anisotropy in the electrical resistivity of Weyl metals at low temperatures, where the electrical resistivity becomes much reduced when electric fields are applied to the direction of the momentum vector to connect two paired Weyl points. Performing the renormalization group analysis, we find that the distance between two Weyl points becomes enhanced logarithmically at low temperatures although the coupling constant of such interactions vanishes inverse-logarithmically. Considering the Adler-Bell-Jackiw anomaly, scattering between these two Weyl points becomes suppressed to increase electrical conductivity in the “longitudinal” direction, counter intuitive in the respect that interactions are expected to reduce metallicity. We also propose that the anomalous contribution in the Hall effect shows the logarithmic enhancement as a function of temperature, originating from the fact that the anomalous Hall coefficient turns out to be proportional to the distance between two paired Weyl points. Correlations with topological constraints allow unexpected and exotic transport properties.
Weyl gravity and Cartan geometry
NASA Astrophysics Data System (ADS)
Attard, J.; François, J.; Lazzarini, S.
2016-04-01
We point out that the Cartan geometry known as the second-order conformal structure provides a natural differential geometric framework underlying gauge theories of conformal gravity. We are concerned with two theories: the first one is the associated Yang-Mills-like Lagrangian, while the second, inspired by [1], is a slightly more general one that relaxes the conformal Cartan geometry. The corresponding gauge symmetry is treated within the Becchi-Rouet-Stora-Tyutin language. We show that the Weyl gauge potential is a spurious degree of freedom, analogous to a Stueckelberg field, that can be eliminated through the dressing field method. We derive sets of field equations for both the studied Lagrangians. For the second one, they constrain the gauge field to be the "normal conformal Cartan connection.''Finally, we provide in a Lagrangian framework a justification of the identification, in dimension 4, of the Bach tensor with the Yang-Mills current of the normal conformal Cartan connection, as proved in [2].
Thermoelectric transport in double-Weyl semimetals
NASA Astrophysics Data System (ADS)
Chen, Qi; Fiete, Gregory A.
2016-04-01
We study the thermoelectric properties of a double-Weyl fermion system, possibly realized in HgCr2Se4 and SrSi2, by a semiclassical Boltzmann transport theory. We investigate different relaxation processes including short-range disorder and electron-electron interaction on the thermoelectric transport coefficients. It is found that the anisotropy of the band dispersion for in-plane and out-of-plane momentum directions affects the relaxation time for transport in different directions. The transport also exhibits an interesting directional dependence on the chemical potential and model parameters, differing from a simple isotropic quadratic or linearly dispersing electron gas. By applying a static magnetic field along the linearly dispersing direction, the longitudinal and transverse electrical and thermal magnetoconductivity show a similar dependence on the in-plane cyclotron frequency to the linear dispersing Weyl nodes. By including internode scattering, we find that the chiral anomaly contribution to the thermoelectric coefficients doubles that of a linearly dispersing Weyl node in both the semiclassical and quantum regimes. A magnetic field applied along the quadratically dispersing direction will split the double-Weyl point into two single-Weyl points with the same chirality.
Phase diagrams of disordered Weyl semimetals
NASA Astrophysics Data System (ADS)
Shapourian, Hassan; Hughes, Taylor L.
2016-02-01
Weyl semimetals are gapless quasitopological materials with a set of isolated nodal points forming their Fermi surface. They manifest their quasitopological character in a series of topological electromagnetic responses including the anomalous Hall effect. Here, we study the effect of disorder on Weyl semimetals while monitoring both their nodal/semimetallic and topological properties through computations of the localization length and the Hall conductivity. We examine three different lattice tight-binding models which realize the Weyl semimetal in part of their phase diagram and look for universal features that are common to all of the models, and interesting distinguishing features of each model. We present detailed phase diagrams of these models for large system sizes and we find that weak disorder preserves the nodal points up to the diffusive limit, but does affect the Hall conductivity. We show that the trend of the Hall conductivity is consistent with an effective picture in which disorder causes the Weyl nodes move within the Brillouin zone along a specific direction that depends deterministically on the properties of the model and the neighboring phases to the Weyl semimetal phase. We also uncover an unusual (nonquantized) anomalous Hall insulator phase which can only exist in the presence of disorder.
Spiraling Fermi arcs in Weyl materials
NASA Astrophysics Data System (ADS)
Li, Songci; Andreev, Anton
In Weyl materials the valence and conduction electron bands touch at an even number of isolated points in the Brillouin zone. In the vicinity of these points the electron dispersion is linear and may be described by the massless Dirac equation. This results in nontrivial topology of Berry connection curvature. One of its consequences is the existence of peculiar surface electron states whose Fermi surfaces form arcs connecting projections of the Weyl points onto the surface plane. Band bending near the boundary of the crystal also produces surface states. We show that in Weyl materials band bending near the crystal surface gives rise to spiral structure of energy surfaces of arc states. The corresponding Fermi surface has the shape of a spiral that winds about the projection of the Weyl point onto the surface plane. The direction of the winding is determined by the helicity of the Weyl point and the sign of the band bending potential. For close valleys arc state morphology may be understood in terms of avoided crossing of oppositely winding spirals. This work is supported by the U.S. Department of Energy Office of Science, Basic Energy Sciences under Award Number DE-FG02-07ER46452.
Electromagnetic response of interacting Weyl semimetals
NASA Astrophysics Data System (ADS)
Jacobs, V. P. J.; Betzios, Panagiotis; Gürsoy, Umut; Stoof, H. T. C.
2016-05-01
We study the electromagnetic properties of Weyl semimetals with strong interactions. Aiming for a large-N expansion, we induce strong interactions by coupling a Weyl fermion with a tunable coupling constant gf to a quantum critical system with a large number of order O (N ) fermionic and bosonic degrees of freedom. The critical fluctuations are described by a conformal field theory containing also fermionic composite operators with scaling dimension Δ . Employing the methods of the holographic correspondence, we then derive the effective theory of the Weyl fermions in the presence of external electric and magnetic fields in the large-N limit. In particular, we determine their frequency and momentum-dependent anomalous magnetic moment. We also determine the conductivity of the Weyl semimetal including the vertex corrections consistent with the Ward identity. Finally, we connect our construction to the case of Coulomb interactions in Weyl semimetals by tuning the parameters Δ →5 /2 and gf2→e /√{ℏ c ɛ0 } .
Ageitos, Jose Manuel; Yazawa, Kenjiro; Tateishi, Ayaka; Tsuchiya, Kousuke; Numata, Keiji
2016-01-11
The chemoenzymatic polymerization of amino acid monomers by proteases involves a two-step reaction: the formation of a covalent acyl-intermediate complex between the protease and the carboxyl ester group of the monomer and the subsequent deacylation of the complex by aminolysis to form a peptide bond. Although the initiation with the ester group of the monomer is an important step, the influence of the ester group on the polymerization has not been studied in detail. Herein, we studied the effect of the ester groups (methyl, ethyl, benzyl, and tert-butyl esters) of alanine and glycine on the synthesis of peptides using papain as the catalyst. Alanine and glycine were selected as monomers because of their substantially different affinities toward papain. The efficiency of the polymerization of alanine and glycine benzyl esters was much greater than that of the other esters. The benzyl ester group therefore allowed papain to equally polymerize alanine and glycine, even though the affinity of alanine toward papain is substantially higher. The characterization of the copolymers of alanine and glycine in terms of the secondary structure and thermal properties revealed that the thermal stability of the peptides depends on the amino acid composition and resultant secondary structure. The current results indicate that the nature of the ester group drastically affects the polymerization efficiency and broadens the substrate specificity of the protease. PMID:26620763
NASA Astrophysics Data System (ADS)
Cardoso, Jorge G.
2015-11-01
It is assumed that the two-component spinor formalisms for curved spacetimes that are endowed with torsionful affine connexions can supply a local description of dark energy in terms of classical massive spin-one uncharged fields. The relevant wave functions are related to torsional affine potentials which bear invariance under the action of the generalized Weyl gauge group. Such potentials are thus taken to carry an observable character and emerge from contracted spin affinities whose patterns are chosen in a suitable way. New covariant calculational techniques are then developed towards deriving explicitly the wave equations that supposedly control the propagation in spacetime of the dark energy background. What immediately comes out of this derivation is a presumably natural display of interactions between the fields and both spin torsion and curvatures. The physical properties that may arise directly fromthe solutions to thewave equations are not brought out.
Metaplectic Representation, Conley-Zehnder Index, and Weyl Calculus on Phase Space
NASA Astrophysics Data System (ADS)
de Gosson, Maurice
We define and study a metaplectically covariant class of pseudo-differential operators acting on functions on symplectic space and generalizing a modified form of the usual Weyl calculus. This construction requires a precise calculation of the twisted Weyl symbol of a class of generators of the metaplectic group and the use of a Conley-Zehnder type index for symplectic paths, defined without restrictions on the endpoint. Our calculus is related to the usual Weyl calculus using a family of isometries of L2(ℝn) on closed subspaces of L2(ℝ2n) and to an irreducible representation of the Heisenberg algebra distinct from the usual Schrödinger representation.
Optical conductivity of disordered Weyl semimetals in collisionless regime at zero temperature
NASA Astrophysics Data System (ADS)
Juricic, Vladimir; Roy, Bitan
Weyl semimetals have recently attracted considerable attention as prime examples of topologically nontrivial gapless states of quantum matter. They have been experimentally found and the chiral anomaly, which represents their hallmark feature, has been measured. In this work, we study transport in the disordered Weyl semimetals using the Kubo formalism. We consider point-like impurity potentials, which are irrelevant in the renormalization-group sense, and compute the corresponding leading correction to the collisionless conductivity at zero temperature. As a result, we find that all eight possible types of the point-like disorder potentials give rise to a correction to the real part of the optical conductivity in the clean limit, which is universal up to a sign. Consequently, the dielectric constant of a Weyl material receives a disorder correction which is linear in frequency. Finally, we discuss some experimental consequences of our findings.
ERIC Educational Resources Information Center
Gray, Gary R.
1980-01-01
Presents selected recent advances in immobilization chemistry which have important connections to affinity chromatography. Discusses ligand immobilization and support modification. Cites 51 references. (CS)
Quantum transport in Dirac materials: Signatures of tilted and anisotropic Dirac and Weyl cones
NASA Astrophysics Data System (ADS)
Trescher, Maximilian; Sbierski, Björn; Brouwer, Piet W.; Bergholtz, Emil J.
2015-03-01
We calculate conductance and noise for quantum transport at the nodal point for arbitrarily tilted and anisotropic Dirac or Weyl cones. Tilted and anisotropic dispersions are generic in the absence of certain discrete symmetries, such as particle-hole and lattice point group symmetries. Whereas anisotropy affects the conductance g , but leaves the Fano factor F (the ratio of shot noise power and current) unchanged, a tilt affects both g and F . Since F is a universal number in many other situations, this finding is remarkable. We apply our general considerations to specific lattice models of strained graphene and a pyrochlore Weyl semimetal.
The Weyl tensor correlator in cosmological spacetimes
Fröb, Markus B.
2014-12-01
We give a general expression for the Weyl tensor two-point function in a general Friedmann-Lemaître-Robertson-Walker spacetime. We work in reduced phase space for the perturbations, i.e., quantize only the dynamical degrees of freedom without adding any gauge-fixing term. The general formula is illustrated by a calculation in slow-roll single-field inflation to first order in the slow-roll parameters ε and δ, and the result is shown to have the correct de Sitter limit as ε, δ → 0. Furthermore, it is seen that the Weyl tensor correlation function in slow-roll does not suffer from infrared divergences, unlike the two-point functions of the metric and scalar field perturbations. Lastly, we show how to recover the usual tensor power spectrum from the Weyl tensor correlation function.
The Weyl tensor correlator in cosmological spacetimes
Fröb, Markus B.
2014-12-05
We give a general expression for the Weyl tensor two-point function in a general Friedmann-Lemaître-Robertson-Walker spacetime. We work in reduced phase space for the perturbations, i.e., quantize only the dynamical degrees of freedom without adding any gauge-fixing term. The general formula is illustrated by a calculation in slow-roll single-field inflation to first order in the slow-roll parameters ϵ and δ, and the result is shown to have the correct de Sitter limit as ϵ,δ→0. Furthermore, it is seen that the Weyl tensor correlation function in slow-roll does not suffer from infrared divergences, unlike the two-point functions of the metric and scalar field perturbations. Lastly, we show how to recover the usual tensor power spectrum from the Weyl tensor correlation function.
Photoinduced Anomalous Hall Effects in Weyl Semimetals
NASA Astrophysics Data System (ADS)
Chan, Ching-Kit; Lee, Patrick A.; Burch, Kenneth S.; Han, Jung Hoon; Ran, Ying
We examine theoretically the interplay between chiral photons and chiral electrons in Weyl semimetals. Owing to its monopole nature, a three-dimensional Weyl node is topologically-robust against a circularly polarized light. A driven Weyl system exhibits node shifts in the momentum space, in sharp contrast to the gap opening in a driven two-dimensional Dirac system. We show that the node shift leads to a change of the Chern vector which gives arise to a net photoinduced anomalous Hall conductivity, in the plane perpendicular to the light propagation. We shall describe the basic idea behind this generic photoinduced Hall effect, illustrate it with a concrete microscope model, and estimate its feasibility based on current optical experimental techniques.
Hereditarily polaroid operators, SVEP and Weyl's theorem
NASA Astrophysics Data System (ADS)
Duggal, B. P.
2008-04-01
A Banach space operator is hereditarily polaroid, , if every part of T is polaroid. operators have SVEP. It is proved that if has SVEP and is a Riesz operator which commutes with T, then T+R satisfies generalized a-Browder's theorem. If, in particular, R is a quasi-nilpotent operator Q, then both T+Q and T*+Q* satisfy generalized a-Browder's theorem; furthermore, if Q is injective, then also T+Q satisfies Weyl's theorem. If is an algebraic operator which commutes with the polynomially operator T, then T+N is polaroid and has SVEP, f(T+N) satisfies generalized Weyl's theorem for every function f which is analytic on a neighbourhood of [sigma](T+N), and f(T+N)* satisfies generalized a-Weyl's theorem for every function f which is analytic on, and constant on no component of, a neighbourhood of [sigma](T+N).
The Weyl law for contractive maps
NASA Astrophysics Data System (ADS)
Spina, Maria E.; Rivas, Alejandro M. F.; Carlo, Gabriel
2013-11-01
We find an empirical Weyl law followed by the eigenvalues of contractive maps. An important property is that it is mainly insensitive to the dimension of the corresponding invariant classical set, the strange attractor. The usual explanation for the fractal Weyl law emergence in scattering systems (i.e., having a projective opening) is based on the classical phase space distributions evolved up to the quantum to classical correspondence (Ehrenfest) time. In the contractive case this reasoning fails to describe it. Instead, we conjecture that the support for this behavior is essentially given by the strong non-orthogonality of the eigenvectors of the contractive superoperator. We test the validity of the Weyl law and this conjecture on two paradigmatic systems, the dissipative baker and kicked top maps.
A first look at Weyl anomalies in shape dynamics
Gomes, Henrique
2013-11-15
One of the more popular objections towards shape dynamics is the suspicion that anomalies in the spatial Weyl symmetry will arise upon quantization. The purpose of this short paper is to establish the tools required for an investigation of the sort of anomalies that can possibly arise. The first step is to adapt to our setting Barnich and Henneaux's formulation of gauge cohomology in the Hamiltonian setting, which serve to decompose the anomaly into a spatial component and time component. The spatial part of the anomaly, i.e., the anomaly in the symmetry algebra itself ([Ω, Ω] ∝ ℏ instead of vanishing) is given by a projection of the second ghost cohomology of the Hamiltonian BRST differential associated to Ω, modulo spatial derivatives. The temporal part, [Ω, H] ∝ ℏ is given by a different projection of the first ghost cohomology and an extra piece arising from a solution to a functional differential equation. Assuming locality of the gauge cohomology groups involved, this part is always local. Assuming locality for the gauge cohomology groups, using Barnich and Henneaux's results, the classification of Weyl cohomology for higher ghost numbers performed by Boulanger, and following the descent equations, we find a complete characterizations of anomalies in 3+1 dimensions. The spatial part of the anomaly and the first component of the temporal anomaly are always local given these assumptions even in shape dynamics. The part emerging from the solution of the functional differential equations explicitly involves the shape dynamics Hamiltonian, and thus might be non-local. If one restricts this extra piece of the temporal anomaly to be also local, then overall no Weyl anomalies, either temporal or spatial, emerge in the 3+1 case.
The repulsive Casimir effect in Weyl semimetals
NASA Astrophysics Data System (ADS)
Wilson, Justin; Allocca, Andrew; Galitski, Victor
2015-03-01
Weyl semimetals are a proposed topological material with broken time-reversal symmetry. Due to this, they experience a particular bulk Hall effect as well as a weak longitudinal conductance. In such a situation, one can see a repulsive Casimir effect between two Weyl semimetals (similar to what has been studied for topological insulators and quantum hall materials), and the effect can be tuned from attractive to repulsive with chemical potential or magnetic field. We consider, separately, a simplified bulk description and a thin film geometry taking into account the band structure. This work is supported by JQI-PFC.
Acoustic Faraday rotation in Weyl semimetals
NASA Astrophysics Data System (ADS)
Liu, Donghao; Shi, Junren
We investigate the phonon problems in Weyl semimetals, from which both the phonon Berry curvature and the phonon Damping could be obtained. We show that even without a magnetic field, the degenerate transverse acoustic modes could also be split due to the adiabatic curvature. In three dimensional case, acoustic Faraday rotation shows up. And furthermore, since the attenuation procedure could distinguish the polarized mode, single circularly polarized acoustic wave could be realized. We study the mechanism in the novel time reversal symmetry broken Weyl semimetal. New effects rise because of the linear dispersion, which give enlightenment in the measurement of this new kind of three-dimensional material.
Barrantes, R; Smouse, P E; Mohrenweiser, H W; Gershowitz, H; Azofeifa, J; Arias, T D; Neel, J V
1990-01-01
There is evidence that Amerindians have continuously occupied the lower Central American Isthmus for as long as 10,000 years. There remains some doubt about the relationships of these original colonizers to the resident peoples of this zone at the time of European contact (approximately A.D. 1500). We present new genetic data for up to 48 genetic loci for 570 members of six Chibcha-speaking tribes of lower Central America--the Boruca, Bribri, Cabecar, and Guatuso of Costa Rica and the Kuna and Teribe of Panama--and delineate the genetic affinities among the various groups (these six tribes and the Guaymi and Bokota) of lower Central America. We convert standard genetic distance metrics into a form that is linear with the effective time since divergence, and we compare the genetic distances with linguistic distances for the same groups (r = .74, P less than .001). Geographic affinity accounts for some of the genetic divergence among groups (r = .49, P less than .084) and for some of the linguistic divergence (r = .53, P less than .037), but the correspondence between geographic position and taxonomic affinity is not high. We combine all of the genetic and linguistic data to construct a synthetic overview taxonomy of the lower Central American Chibcha. Both the genetic and linguistic data exhibit hierarchical organization of tribal groups, showing a general east-to-west pattern of grouping, with greater affinities between close neighbors. The presence of private genetic variants of some antiquity within the region and their absence outside the zone, coupled with the essential absence of the DI*A polymorphism of mongoloid origin that is widespread outside the zone, argue for a relatively isolated development of the Central American Chibcha. Our results do not support the old view of lower Central America as a frontier between more advanced cultures to the north and south. Any such explanation would require recent waves of migration from outside the region, migration
Dirty Weyl semimetals: Stability, phase transition, and quantum criticality
NASA Astrophysics Data System (ADS)
Bera, Soumya; Sau, Jay D.; Roy, Bitan
2016-05-01
We study the stability of three-dimensional incompressible Weyl semimetals in the presence of random quenched charge impurities. Combining numerical analysis and scaling theory, we show that, in the presence of sufficiently weak randomness, (i) the Weyl semimetal remains stable, while (ii) the double-Weyl semimetal gives rise to compressible diffusive metal where the mean density of states at zero energy is finite. At stronger disorder, the Weyl semimetal undergoes a quantum phase transition and enter into a metallic phase. The mean density of states at zero energy serves as the order parameter and displays single-parameter scaling across such a disorder driven quantum phase transition. We numerically determine various exponents at the critical point, which appear to be insensitive to the number of Weyl pairs. We also extract the extent of the quantum critical regime in disordered Weyl semimetals and the phase diagram of dirty double-Weyl semimetals at finite energies.
Prediction of Weyl semimetal in orthorhombic MoTe2
NASA Astrophysics Data System (ADS)
Sun, Yan; Wu, Shu-Chun; Ali, Mazhar N.; Felser, Claudia; Yan, Binghai
2015-10-01
We investigate the orthorhombic phase (Td) of the layered transition-metal dichalcogenide MoTe2 as a Weyl semimetal candidate. MoTe2 exhibits four pairs of Weyl points lying slightly above (˜6 meV ) the Fermi energy in the bulk band structure. Different from its cousin WTe2, which was recently predicted to be a type-II Weyl semimetal, the spacing between each pair of Weyl points is found to be as large as 4% of the reciprocal lattice in MoTe2 (six times larger than that of WTe2). When projected onto the surface, the Weyl points are connected by Fermi arcs, which can be easily accessed by angle-resolved photoemission spectroscopy due to the large Weyl point separation. In addition, we show that the correlation effect or strain can drive MoTe2 from a type-II to a type-I Weyl semimetal.
NASA Astrophysics Data System (ADS)
Cerba Diaconescu, Oxana; Schlomiuk, Dana; Vulpe, Nicolae
In this article, we consider the class QSL4{u +vc+w^c, ∞ } of all real quadratic differential systems (dx)/(dt) = p(x, y), (dy)/(dt) = q(x, y) with gcd(p, q) = 1, having invariant lines of total multiplicity four and two complex and one real infinite singularities. We first construct compactified canonical forms for the class QSL4{u +vc+w^c, ∞ } so as to include limit points in the 12-dimensional parameter space of this class. We next construct the bifurcation diagrams for these compactified canonical forms. These diagrams contain many repetitions of phase portraits and we show that these are due to many symmetries under the group action. To retain the essence of the dynamics we finally construct the quotient spaces under the action of the group G = Aff(2, R) × R* of affine transformations and time homotheties and we place the phase portraits in these quotient spaces. The final diagrams retain only the necessary information to capture the dynamics under the motion in the parameter space as well as under this group action. We also present here necessary and sufficient conditions for an affine line to be invariant of multiplicity k for a quadratic system.
NASA Astrophysics Data System (ADS)
Doikou, Anastasia; Ioannidou, Theodora
2011-04-01
A non-compact version of the Weyl equation is proposed, based on the infinite dimensional spin zero representation of the mathfrak{s}{mathfrak{l}_2} algebra. Solutions of the aforementioned equation are obtained in terms of the Kummer functions. In this context, we discuss the ADHMN approach in order to construct the corresponding non-compact BPS monopoles.
Weyl Nodes in Trigonal Tellurium and Selenium
NASA Astrophysics Data System (ADS)
Hirayama, Motoaki; Okugawa, Ryo; Ishibashi, Shoji; Murakami, Shuichi; Miyake, Takashi
2015-03-01
Singular points in the momentum space (Dirac nodes) have been under intensive investigation recently. Among various Dirac systems, materials having three-dimensional Dirac nodes without spin degeneracy (Weyl nodes) are of particular interest because of their topological nature. We study trigonal Te and Se as systems having both strong spin-orbit interaction (SOI) and broken inversion symmetry, which is necessary for the Weyl node. We calculate the electronic structure by using QMAS based on relativistic density functional theory, and add the self-energy correction in the GW approximation. Te and Se are insulating at ambient pressure. The conduction bands have a spin splitting similar to the Rashba splitting around the H points, but unlike the Rashba splitting the spin directions are radial, forming a hedgehog spin texture. The energy gap decreases with increasing pressure. In the metallic phase, the spin rotates twice around H on the kz = +/- π/c plane, which can be explained by the motion of the Weyl nodes under pressure. We also find that trigonal Te shows the Weyl semimetal phase with time-reversal symmetry under pressure.
Agatsuma, T; Iwagami, M; Liu, C X; Rajapakse, R P V J; Mondal, M M H; Kitikoon, V; Ambu, S; Agatsuma, Y; Blair, D; Higuchi, T
2002-03-01
Schistosoma species have traditionally been arranged in groups based on egg morphology, geographical origins, and the genus or family of snail intermediate host. One of these groups is the 'S. indicum group' comprising species from Asia that use pulmonate snails as intermediate hosts. DNA sequences were obtained from the four members of this group (S. indicum, S. spindale, S. nasale and S. incognitum) to provide information concerning their phylogenetic relationships with other Asian and African species and species groups. The sequences came from the second internal transcribed spacer (ITS2) of the ribosomal gene repeat, part of the 28S ribosomal RNA gene (28S), and part of the mitochondrial cytochrome c oxidase subunit 1 (CO1) gene. Tree analyses using both distance and parsimony methods showed the S. indicum group not to be monophyletic. Schistosoma indicum, S. spindale and S. nasale were clustered among African schistosomes, while S. incognitum was placed as sister to the African species (using ITS2 and 28S nucleotide sequences and CO1 amino acid sequences), or as sister to all other species of Schistosoma (CO1 nucleotide sequences). Based on the present molecular data, a scenario for the evolution of the S. indicum group is discussed. PMID:12018199
ERIC Educational Resources Information Center
Keddie, Amanda
2004-01-01
This paper describes the research approach of a case study ethnography. The study sought to explore the peer group understandings of five male friends aged between six and eight years. In exploring the social dynamics of peer culture, and in particular how these dynamics interacted to define, regulate and maintain particular understandings of…
Piché-Choquette, Sarah; Tremblay, Julien; Tringe, Susannah G.
2016-01-01
Soil microbial communities are continuously exposed to H2 diffusing into the soil from the atmosphere. N2-fixing nodules represent a peculiar microniche in soil where H2 can reach concentrations up to 20,000 fold higher than in the global atmosphere (0.530 ppmv). In this study, we investigated the impact of H2 exposure on soil bacterial community structure using dynamic microcosm chambers simulating soil H2 exposure from the atmosphere and N2-fixing nodules. Biphasic kinetic parameters governing H2 oxidation activity in soil changed drastically upon elevated H2 exposure, corresponding to a slight but significant decay of high affinity H2-oxidizing bacteria population, accompanied by an enrichment or activation of microorganisms displaying low-affinity for H2. In contrast to previous studies that unveiled limited response by a few species, the relative abundance of 958 bacterial ribotypes distributed among various taxonomic groups, rather than a few distinct taxa, was influenced by H2 exposure. Furthermore, correlation networks showed important alterations of ribotype covariation in response to H2 exposure, suggesting that H2 affects microbe-microbe interactions in soil. Taken together, our results demonstrate that H2-rich environments exert a direct influence on soil H2-oxidizing bacteria in addition to indirect effects on other members of the bacterial communities. PMID:26989620
Bruna-Larenas, Tamara; Gómez-Jeria, Juan S
2012-01-01
We report the results of a search for model-based relationships between mu, delta, and kappa opioid receptor binding affinity and molecular structure for a group of molecules having in common a morphine structural core. The wave functions and local reactivity indices were obtained at the ZINDO/1 and B3LYP/6-31G(∗∗) levels of theory for comparison. New developments in the expression for the drug-receptor interaction energy expression allowed several local atomic reactivity indices to be included, such as local electronic chemical potential, local hardness, and local electrophilicity. These indices, together with a new proposal for the ordering of the independent variables, were incorporated in the statistical study. We found and discussed several statistically significant relationships for mu, delta, and kappa opioid receptor binding affinity at both levels of theory. Some of the new local reactivity indices incorporated in the theory appear in several equations for the first time in the history of model-based equations. Interaction pharmacophores were generated for mu, delta, and kappa receptors. We discuss possible differences regulating binding and selectivity in opioid receptor subtypes. This study, contrarily to the statistically backed ones, is able to provide a microscopic insight of the mechanisms involved in the binding process. PMID:25379287
Bruna-Larenas, Tamara; Gómez-Jeria, Juan S.
2012-01-01
We report the results of a search for model-based relationships between mu, delta, and kappa opioid receptor binding affinity and molecular structure for a group of molecules having in common a morphine structural core. The wave functions and local reactivity indices were obtained at the ZINDO/1 and B3LYP/6-31G∗∗ levels of theory for comparison. New developments in the expression for the drug-receptor interaction energy expression allowed several local atomic reactivity indices to be included, such as local electronic chemical potential, local hardness, and local electrophilicity. These indices, together with a new proposal for the ordering of the independent variables, were incorporated in the statistical study. We found and discussed several statistically significant relationships for mu, delta, and kappa opioid receptor binding affinity at both levels of theory. Some of the new local reactivity indices incorporated in the theory appear in several equations for the first time in the history of model-based equations. Interaction pharmacophores were generated for mu, delta, and kappa receptors. We discuss possible differences regulating binding and selectivity in opioid receptor subtypes. This study, contrarily to the statistically backed ones, is able to provide a microscopic insight of the mechanisms involved in the binding process. PMID:25379287
Magneto-optic measurements of the Weyl semimetal NbAs
NASA Astrophysics Data System (ADS)
Armstrong, Nathan; Shao, Yinming; Yuan, Zhujun; Jia, Shuang; Basov, D. N.; Timusk, Thomas
NbAs is among the newly discovered Weyl semimetals that are of great interest because they have the potential to confirm the chiral anomaly predicted by particle physics. It has been theorized that two separated Weyl nodes of opposite chirality can have a chiral current flow between them with the application electric and magnetic fields parallel to the displacement of the nodes. Indeed, magnetoresistance measurements on TaAs and NbAs found a negative magnetoresistance with these fields. ARPES and band structure calculations show that NbAs has two different groups of Weyl nodes with all the node splittings in kx -ky planes. In addition to the Weyl nodes there are other trivial bands that create Fermi pockets elsewhere in the BZ that are also observed in reflectance measurements. We will present magneto-optics results from far infrared optical data of NbAs in Voigt geometry up to 8 Tesla. In the far infrared at large fields there are two strong features that show an 11% and 3% change of reflectance in field at 60 and 480 cm-1 , respectively. We evaluate these data with comparison to the above mentioned band structure of NbAs.
Elastic Gauge Fields in Weyl Semimetals
NASA Astrophysics Data System (ADS)
Cortijo, Alberto; Ferreiros, Yago; Landsteiner, Karl; Hernandez Vozmediano, Maria Angeles
We show that, as it happens in graphene, elastic deformations couple to the electronic degrees of freedom as pseudo gauge fields in Weyl semimetals. We derive the form of the elastic gauge fields in a tight-binding model hosting Weyl nodes and see that this vector electron-phonon coupling is chiral, providing an example of axial gauge fields in three dimensions. As an example of the new response functions that arise associated to these elastic gauge fields, we derive a non-zero phonon Hall viscosity for the neutral system at zero temperature. The axial nature of the fields provides a test of the chiral anomaly in high energy with three axial vector couplings. European Union structural funds and the Comunidad de Madrid MAD2D-CM Program (S2013/MIT-3007).
Mechanical Weyl Modes in Topological Maxwell Lattices
NASA Astrophysics Data System (ADS)
Rocklin, D. Zeb; Chen, Bryan Gin-ge; Falk, Martin; Vitelli, Vincenzo; Lubensky, T. C.
2016-04-01
We show that two-dimensional mechanical lattices can generically display topologically protected bulk zero-energy phonon modes at isolated points in the Brillouin zone, analogs of massless fermion modes of Weyl semimetals. We focus on deformed square lattices as the simplest Maxwell lattices, characterized by equal numbers of constraints and degrees of freedom, with this property. The Weyl points appear at the origin of the Brillouin zone along directions with vanishing sound speed and move away to the zone edge (or return to the origin) where they annihilate. Our results suggest a design strategy for topological metamaterials with bulk low-frequency acoustic modes and elastic instabilities at a particular, tunable finite wave vector.
Repulsive Casimir force between Weyl semimetals
NASA Astrophysics Data System (ADS)
Wilson, Justin H.; Allocca, Andrew A.; Galitski, Victor
2015-06-01
Weyl semimetals are a class of topological materials that exhibit a bulk Hall effect due to time-reversal symmetry breaking. We show that for the idealized semi-infinite case, the Casimir force between two identical Weyl semimetals is repulsive at short range and attractive at long range. Considering plates of finite thickness, we can reduce the size of the long-range attraction even making it repulsive for all distances when thin enough. In the thin-film limit, we study the appearance of an attractive Casimir force at shorter distances due to the longitudinal conductivity. Magnetic field, thickness, and chemical potential provide tunable nobs for this effect, controlling the Casimir force: whether it is attractive or repulsive, the magnitude of the effect, and the positions and existence of a trap and antitrap.
Disordered Weyl Semimetals and Their Topological Family
NASA Astrophysics Data System (ADS)
Zhao, Y. X.; Wang, Z. D.
2015-05-01
We develop a topological theory for disordered Weyl semimetals in the framework of the gauge invariance of the replica formalism and boundary-bulk correspondence of Chern insulators. An anisotropic topological θ term is analytically derived for the effective nonlinear σ model. It is this nontrivial topological term that ensures that the bulk transverse transport of Weyl semimetals is robust against disorders. Moreover, we establish a general diagram that reveals the intrinsic relations among topological terms in the nonlinear σ models and gauge response theories, respectively, for (2 n +2 ) -dimensional topological insulators, (2 n +1 ) -dimensional chiral fermions, (2 n +1 )-dimensional chiral semimetals, and (2 n )-dimensional topological insulators with n being a positive integer.
Mechanical Weyl Modes in Topological Maxwell Lattices.
Rocklin, D Zeb; Chen, Bryan Gin-Ge; Falk, Martin; Vitelli, Vincenzo; Lubensky, T C
2016-04-01
We show that two-dimensional mechanical lattices can generically display topologically protected bulk zero-energy phonon modes at isolated points in the Brillouin zone, analogs of massless fermion modes of Weyl semimetals. We focus on deformed square lattices as the simplest Maxwell lattices, characterized by equal numbers of constraints and degrees of freedom, with this property. The Weyl points appear at the origin of the Brillouin zone along directions with vanishing sound speed and move away to the zone edge (or return to the origin) where they annihilate. Our results suggest a design strategy for topological metamaterials with bulk low-frequency acoustic modes and elastic instabilities at a particular, tunable finite wave vector. PMID:27081989
Weyl semimetal and nonassociative Nambu geometry
NASA Astrophysics Data System (ADS)
Chu, Chong-Sun
2016-03-01
Topological materials are characterized by an electronic band structure with nontrivial topological properties. In this paper we introduce a basis of operators for the linear space of operators spanned by charge-neutral fermion bilinears. These band-projected density operators are constructed using directly the eigenfunctions of the electronic energy band structure and there is no need to assume a flat Berry curvature. As a result, our set of operators has a wider range of validity and is sensitive to physical phenomena which are not detectable in the flat-curvature limit. In particular, we show that the Berry monopole configuration of a Weyl semimetal give rises to a nonvanishing Jacobiator for these band-projected density operators, implying the emergence of nonassociativity at the location of the Weyl nodes. The resulting nonassociativity observes the fundamental identity, the defining property of the Nambu bracket, and so one may call this a nonassociative Nambu geometry. We also derive the corresponding uncertainty principle.
Stability of the nakedness of Weyl singularities
NASA Technical Reports Server (NTRS)
Haugan, M. P.; Liang, E. P. T.
1979-01-01
The stability of the nakedness of the Weyl singularities against matter perturbations is investigated. Consideration is given to the effects of infalling test matter on the convergence of outgoing null rays. It is shown that the additional convergence induced by infalling test matter does not blow up sufficiently fast to reconverge diverging outgoing rays, at least in the equator, and that the nakedness seems to be stable in this limited sense.
Weyl superfluidity in a three-dimensional dipolar Fermi gas.
Liu, Bo; Li, Xiaopeng; Yin, Lan; Liu, W Vincent
2015-01-30
Weyl superconductivity or superfluidity, a fascinating topological state of matter, features novel phenomena such as emergent Weyl fermionic excitations and anomalies. Here we report that an anisotropic Weyl superfluid state can arise as a low temperature stable phase in a 3D dipolar Fermi gas. A crucial ingredient of our model is a direction-dependent two-body effective attraction generated by a rotating external field. Experimental signatures are predicted for cold gases in radio-frequency spectroscopy. The finite temperature phase diagram of this system is studied and the transition temperature of the Weyl superfluidity is found to be within the experimental scope for atomic dipolar Fermi gases. PMID:25679898
Observation of Weyl nodes and Fermi arcs in tantalum phosphide
Xu, N.; Weng, H. M.; Lv, B. Q.; Matt, C. E.; Park, J.; Bisti, F.; Strocov, V. N.; Gawryluk, D.; Pomjakushina, E.; Conder, K.; Plumb, N. C.; Radovic, M.; Autès, G.; Yazyev, O. V.; Fang, Z.; Dai, X.; Qian, T.; Mesot, J.; Ding, H.; Shi, M.
2016-01-01
A Weyl semimetal possesses spin-polarized band-crossings, called Weyl nodes, connected by topological surface arcs. The low-energy excitations near the crossing points behave the same as massless Weyl fermions, leading to exotic properties like chiral anomaly. To have the transport properties dominated by Weyl fermions, Weyl nodes need to locate nearly at the chemical potential and enclosed by pairs of individual Fermi surfaces with non-zero Fermi Chern numbers. Combining angle-resolved photoemission spectroscopy and first-principles calculation, here we show that TaP is a Weyl semimetal with only a single type of Weyl fermions, topologically distinguished from TaAs where two types of Weyl fermions contribute to the low-energy physical properties. The simple Weyl fermions in TaP are not only of fundamental interests but also of great potential for future applications. Fermi arcs on the Ta-terminated surface are observed, which appear in a different pattern from that on the As-termination in TaAs and NbAs. PMID:26983910
Helical Spin Order from Topological Dirac and Weyl Semimetals
NASA Astrophysics Data System (ADS)
Sun, Xiao-Qi; Zhang, Shou-Cheng; Wang, Zhong
2015-08-01
We study dynamical mass generation and the resultant helical spin orders in topological Dirac and Weyl semimetals, including the edge states of quantum spin Hall insulators, the surface states of weak topological insulators, and the bulk materials of Weyl semimetals. In particular, the helical spin textures of Weyl semimetals manifest the spin-momentum locking of Weyl fermions in a visible manner. The spin-wave fluctuations of the helical order carry electric charge density; therefore, the spin textures can be electrically controlled in a simple and predictable manner.
Observation of Weyl nodes and Fermi arcs in tantalum phosphide
NASA Astrophysics Data System (ADS)
Xu, N.; Weng, H. M.; Lv, B. Q.; Matt, C. E.; Park, J.; Bisti, F.; Strocov, V. N.; Gawryluk, D.; Pomjakushina, E.; Conder, K.; Plumb, N. C.; Radovic, M.; Autès, G.; Yazyev, O. V.; Fang, Z.; Dai, X.; Qian, T.; Mesot, J.; Ding, H.; Shi, M.
2016-03-01
A Weyl semimetal possesses spin-polarized band-crossings, called Weyl nodes, connected by topological surface arcs. The low-energy excitations near the crossing points behave the same as massless Weyl fermions, leading to exotic properties like chiral anomaly. To have the transport properties dominated by Weyl fermions, Weyl nodes need to locate nearly at the chemical potential and enclosed by pairs of individual Fermi surfaces with non-zero Fermi Chern numbers. Combining angle-resolved photoemission spectroscopy and first-principles calculation, here we show that TaP is a Weyl semimetal with only a single type of Weyl fermions, topologically distinguished from TaAs where two types of Weyl fermions contribute to the low-energy physical properties. The simple Weyl fermions in TaP are not only of fundamental interests but also of great potential for future applications. Fermi arcs on the Ta-terminated surface are observed, which appear in a different pattern from that on the As-termination in TaAs and NbAs.
Tunable Weyl Points in Periodically Driven Nodal Line Semimetals.
Yan, Zhongbo; Wang, Zhong
2016-08-19
Weyl semimetals and nodal line semimetals are characterized by linear band touching at zero-dimensional points and one-dimensional lines, respectively. We predict that a circularly polarized light drives nodal line semimetals into Weyl semimetals. The Floquet Weyl points thus obtained are tunable by the incident light, which enables investigations of them in a highly controllable manner. The transition from nodal line semimetals to Weyl semimetals is accompanied by the emergence of a large and tunable anomalous Hall conductivity. Our predictions are experimentally testable by transport measurement in film samples or by pump-probe angle-resolved photoemission spectroscopy. PMID:27588882
Observation of Weyl nodes and Fermi arcs in tantalum phosphide.
Xu, N; Weng, H M; Lv, B Q; Matt, C E; Park, J; Bisti, F; Strocov, V N; Gawryluk, D; Pomjakushina, E; Conder, K; Plumb, N C; Radovic, M; Autès, G; Yazyev, O V; Fang, Z; Dai, X; Qian, T; Mesot, J; Ding, H; Shi, M
2016-01-01
A Weyl semimetal possesses spin-polarized band-crossings, called Weyl nodes, connected by topological surface arcs. The low-energy excitations near the crossing points behave the same as massless Weyl fermions, leading to exotic properties like chiral anomaly. To have the transport properties dominated by Weyl fermions, Weyl nodes need to locate nearly at the chemical potential and enclosed by pairs of individual Fermi surfaces with non-zero Fermi Chern numbers. Combining angle-resolved photoemission spectroscopy and first-principles calculation, here we show that TaP is a Weyl semimetal with only a single type of Weyl fermions, topologically distinguished from TaAs where two types of Weyl fermions contribute to the low-energy physical properties. The simple Weyl fermions in TaP are not only of fundamental interests but also of great potential for future applications. Fermi arcs on the Ta-terminated surface are observed, which appear in a different pattern from that on the As-termination in TaAs and NbAs. PMID:26983910
Weyl anomaly and initial singularity crossing
NASA Astrophysics Data System (ADS)
Awad, Adel
2016-04-01
We consider the role of quantum effects, mainly, Weyl anomaly in modifying Friedmann-Lemaitre-Robertson-Walker (FLRW) model singular behavior at early times. Weyl anomaly corrections to FLRW models have been considered in the past, here we reconsider this model and show the following: The singularity of this model is weak according to Tipler and Krolak, therefore, the spacetime might admit a geodesic extension. Weyl anomaly corrections change the nature of the initial singularity from a big bang singularity to a sudden singularity. The two branches of solutions consistent with the semiclassical treatment form a disconnected manifold. Joining these two parts at the singularity provides us with a C1 extension to nonspacelike geodesics and leaves the spacetime geodesically complete. Using Gauss-Codazzi equations one can derive generalized junction conditions for this higher-derivative gravity. The extended spacetime obeys Friedmann and Raychaudhuri equations and the junction conditions. The junction does not generate Dirac delta functions in matter sources which keeps the equation of state unchanged.
Classical probabilities for Majorana and Weyl spinors
Wetterich, C.
2011-08-15
Highlights: > Map of classical statistical Ising model to fermionic quantum field theory. > Lattice-regularized real Grassmann functional integral for single Weyl spinor. > Emerging complex structure characteristic for quantum physics. > A classical statistical ensemble describes a quantum theory. - Abstract: We construct a map between the quantum field theory of free Weyl or Majorana fermions and the probability distribution of a classical statistical ensemble for Ising spins or discrete bits. More precisely, a Grassmann functional integral based on a real Grassmann algebra specifies the time evolution of the real wave function q{sub {tau}}(t) for the Ising states {tau}. The time dependent probability distribution of a generalized Ising model obtains as p{sub {tau}}(t)=q{sub {tau}}{sup 2}(t). The functional integral employs a lattice regularization for single Weyl or Majorana spinors. We further introduce the complex structure characteristic for quantum mechanics. Probability distributions of the Ising model which correspond to one or many propagating fermions are discussed explicitly. Expectation values of observables can be computed equivalently in the classical statistical Ising model or in the quantum field theory for fermions.
Signatures of Weyl semimetals in quasiparticle interference
NASA Astrophysics Data System (ADS)
Mitchell, Andrew K.; Fritz, Lars
2016-01-01
Impurities act as in situ probes of nontrivial electronic structure, causing real-space modulations in the density of states detected by scanning tunneling spectroscopy on the sample surface. We show that distinctive topological features of Weyl semimetals can be revealed in the Fourier transform of this map, interpreted in terms of quasiparticle interference (QPI). We develop an exact Green's function formalism and apply it to generalized models of Weyl semimetals with an explicit surface. The type of perturbation lifting the Dirac node degeneracy to produce the three-dimensional bulk Weyl phase determines the specific QPI signatures appearing on the surface. QPI Fermi arcs may or may not appear, depending on the relative surface orientation and quantum interference effects. Line nodes give rise to tube projections of width controlled by the bias voltage. We consider the effect of crystal warping, distinguishing dispersive arclike features from true Fermi arcs. Finally, we demonstrate that the commonly used joint-density-of-states approach fails qualitatively, and cannot describe QPI extinction.
Unconventional electromagnetic mode in neutral Weyl semimetals
NASA Astrophysics Data System (ADS)
Ferreiros, Yago; Cortijo, Alberto
2016-05-01
We study light propagation in a neutral Weyl semimetal with the Fermi level lying at the Weyl nodes in the weak self-interacting regime. The nontrivial topology induces a screening effect in one of the two transverse gauge fields, for which we find two branches of attenuated collective excitations. In addition to the known topologically gapped photon mode, a different massless and slightly damped excitation appears. Strikingly, at low energies, this excitation has a linear dispersion and it propagates with the same velocity as the electrons, while at energies well above the electron-hole continuum threshold it behaves as a massive attenuated photon with velocity similar to the speed of light in the material. There is a crossover at a certain momentum in the direction perpendicular to the separation of the Weyl nodes above which this gapless mode enters into an overdamped regime. Regarding the unscreened gauge field, we show that it is also attenuated, which is a nontopological property shared by Dirac semimetals as well.
Weyl-gauge symmetry of graphene
Iorio, Alfredo
2011-05-15
Research Highlights: > Graphene action's Weyl symmetry identifies shapes for which the DOS is invariant. > Electrons on graphene might experience a general-relativistic-like spacetime. > Rich mathematical structures, such as the Liouville's equation, naturally arise. - Abstract: The conformal invariance of the low energy limit theory governing the electronic properties of graphene is explored. In particular, it is noted that the massless Dirac theory in point enjoys local Weyl symmetry, a very large symmetry. Exploiting this symmetry in the two spatial dimensions and in the associated three dimensional spacetime, we find the geometric constraints that correspond to specific shapes of the graphene sheet for which the electronic density of states is the same as that for planar graphene, provided the measurements are made in accordance to the inner reference frame of the electronic system. These results rely on the (surprising) general relativistic-like behavior of the graphene system arising from the combination of its well known special relativistic-like behavior with the less explored Weyl symmetry. Mathematical structures, such as the Virasoro algebra and the Liouville equation, naturally arise in this three-dimensional context and can be related to specific profiles of the graphene sheet. Speculations on possible applications of three-dimensional gravity are also proposed.
Robins, P; Jones, C J; Biggerstaff, M; Lindahl, T; Wood, R D
1991-12-01
Complementation group A of xeroderma pigmentosum (XP) represents one of the most prevalent and serious forms of this cancer-prone disorder. Because of a marked defect in DNA excision repair, cells from individuals with XP-A are hypersensitive to the toxic and mutagenic effects of ultraviolet light and many chemical agents. We report here the isolation of the XP-A DNA repair protein by complementation of cell extracts from a repair-defective human XP-A cell line. XP-A protein purified from calf thymus migrates on denaturing gel electrophoresis as a doublet of 40 and 42 kilodaltons. The XP-A protein binds preferentially to ultraviolet light-irradiated DNA, with a preference for damaged over nondamaged nucleotides of approximately 10(3). This strongly suggests that the XP-A protein plays a direct role in the recognition of and incision at lesions in DNA. We further show that this protein corresponds to the product encoded by a recently isolated gene that can restore excision repair to XP-A cells. Thus, excision repair of plasmid DNA by cell extracts sufficiently resembles genomic repair in cells to reveal accurately the repair defect in an inherited disease. The general approach described here can be extended to the identification and isolation of other human DNA repair proteins. PMID:1935910
Robins, P; Jones, C J; Biggerstaff, M; Lindahl, T; Wood, R D
1991-01-01
Complementation group A of xeroderma pigmentosum (XP) represents one of the most prevalent and serious forms of this cancer-prone disorder. Because of a marked defect in DNA excision repair, cells from individuals with XP-A are hypersensitive to the toxic and mutagenic effects of ultraviolet light and many chemical agents. We report here the isolation of the XP-A DNA repair protein by complementation of cell extracts from a repair-defective human XP-A cell line. XP-A protein purified from calf thymus migrates on denaturing gel electrophoresis as a doublet of 40 and 42 kilodaltons. The XP-A protein binds preferentially to ultraviolet light-irradiated DNA, with a preference for damaged over nondamaged nucleotides of approximately 10(3). This strongly suggests that the XP-A protein plays a direct role in the recognition of and incision at lesions in DNA. We further show that this protein corresponds to the product encoded by a recently isolated gene that can restore excision repair to XP-A cells. Thus, excision repair of plasmid DNA by cell extracts sufficiently resembles genomic repair in cells to reveal accurately the repair defect in an inherited disease. The general approach described here can be extended to the identification and isolation of other human DNA repair proteins. Images PMID:1935910
Infinite-Dimensional Schur-Weyl Duality and the Coxeter-Laplace Operator
NASA Astrophysics Data System (ADS)
Tsilevich, N. V.; Vershik, A. M.
2014-05-01
We extend the classical Schur-Weyl duality between representations of the groups and to the case of and the infinite symmetric group . Our construction is based on a "dynamic," or inductive, scheme of Schur-Weyl dualities. It leads to a new class of representations of the infinite symmetric group, which has not appeared earlier. We describe these representations and, in particular, find their spectral types with respect to the Gelfand-Tsetlin algebra. The main example of such a representation acts in an incomplete infinite tensor product. As an important application, we consider the weak limit of the so-called Coxeter-Laplace operator, which is essentially the Hamiltonian of the XXX Heisenberg model, in these representations.
Fractal Weyl law for skew extensions of expanding maps
NASA Astrophysics Data System (ADS)
Jean-François, Arnoldi
2012-06-01
We consider compact Lie group extensions of expanding maps of the circle, essentially restricting to SU(2) extensions. The main objective of the paper is the associated Ruelle transfer (or pull-back) operator \\hat{\\msF} . Harmonic analysis yields a natural decomposition \\hat{\\msF}=\\oplus\\hat{F}_{j} , where j indexes irreducible representation spaces. Using semi-classical techniques we extend a previous result by Faure proving an asymptotic spectral gap for the family \\{\\hat{F}_{j}\\} when restricted to adapted spaces of distributions. Our main result is a fractal Weyl upper bound for the number of eigenvalues (the Ruelle resonances) of these operators out of some fixed disc centred on 0 in the complex plane.
Relativistic corrections to the Moyal-Weyl spacetime
Much, A.
2015-02-15
We use the framework of quantum field theory to obtain by deformation the Moyal-Weyl spacetime. This idea is extracted from recent progress in deformation theory concerning the emergence of the quantum plane of the Landau-quantization. The quantum field theoretical emerging spacetime is not equal to the standard Moyal-Weyl plane, but terms resembling relativistic corrections occur.
Super-Weyl invariance in 5D supergravity
NASA Astrophysics Data System (ADS)
Kuzenko, Sergei M.; Tartaglino-Mazzucchelli, Gabriele
2008-04-01
We propose a superspace formulation for the Weyl multiplet of Script N = 1 conformal supergravity in five dimensions. The corresponding superspace constraints are invariant under super-Weyl transformations generated by a real scalar parameter. The minimal supergravity multiplet, which was introduced by Howe in 1981, emerges if one couples the Weyl multiplet to an Abelian vector multiplet and then breaks the super-Weyl invariance by imposing the gauge condition W = 1, with W the field strength of the vector multiplet. The geometry of superspace is shown to allow the existence of a large family of off-shell supermultiplets that possess uniquely determined super-Weyl transformation laws and can be used to describe supersymmetric matter. Many of these supermultiplets have not appeared within the superconformal tensor calculus. We formulate a manifestly locally supersymmetric and super-Weyl invariant action principle. In the super-Weyl gauge W = 1, this action reduces to that constructed in arXiv:0712.3102. We also present a superspace formulation for the dilaton Weyl multiplet.
Chiral wave-packet scattering in Weyl semimetals
NASA Astrophysics Data System (ADS)
Jiang, Qing-Dong; Jiang, Hua; Liu, Haiwen; Sun, Qing-Feng; Xie, X. C.
2016-05-01
In quantum mechanics, a particle is best described by the wave packet instead of the plane wave. Here, we study the wave-packet scattering problem in Weyl semimetals with the low-energy Weyl fermions of different chiralities. Our results show that the wave packet acquires a chirality-protected shift in the single-impurity scattering process. More importantly, the chirality-protected shift can lead to an anomalous scattering probability, and thus affects the transport properties in Weyl semimetals. We find that the ratio between the transport lifetime and the quantum lifetime increases sharply when the Fermi energy approaches the Weyl nodes, providing an explanation of the experimentally observed ultrahigh mobility in topological (Weyl or Dirac) semimetals.
Floquet Weyl phases in a three-dimensional network model
NASA Astrophysics Data System (ADS)
Wang, Hailong; Zhou, Longwen; Chong, Y. D.
2016-04-01
We study the topological properties of three-dimensional (3D) Floquet band structures, which are defined using unitary evolution matrices rather than Hamiltonians. Previously, two-dimensional band structures of this sort have been shown to exhibit anomalous topological behaviors, such as topologically nontrivial zero-Chern-number phases. We show that the band structure of a 3D network model can exhibit Weyl phases, which feature "Fermi arc" surface states like those found in Weyl semimetals. Tuning the network's coupling parameters can induce transitions between Weyl phases and various topologically distinct gapped phases. We identify a connection between the topology of the gapped phases and the topology of Weyl point trajectories in k space. The model is feasible to realize in custom electromagnetic networks, where the Weyl point trajectories can be probed by scattering parameter measurements.
Holographic p-wave superconductor models with Weyl corrections
NASA Astrophysics Data System (ADS)
Zhang, Lu; Pan, Qiyuan; Jing, Jiliang
2015-04-01
We study the effect of the Weyl corrections on the holographic p-wave dual models in the backgrounds of AdS soliton and AdS black hole via a Maxwell complex vector field model by using the numerical and analytical methods. We find that, in the soliton background, the Weyl corrections do not influence the properties of the holographic p-wave insulator/superconductor phase transition, which is different from that of the Yang-Mills theory. However, in the black hole background, we observe that similarly to the Weyl correction effects in the Yang-Mills theory, the higher Weyl corrections make it easier for the p-wave metal/superconductor phase transition to be triggered, which shows that these two p-wave models with Weyl corrections share some similar features for the condensation of the vector operator.
Magnetic torque anomaly in the quantum limit of Weyl semimetals
Moll, Philip J. W.; Potter, Andrew C.; Nair, Nityan L.; Ramshaw, B. J.; Modic, K. A.; Riggs, Scott; Zeng, Bin; Ghimire, Nirmal J.; Bauer, Eric D.; Kealhofer, Robert; Ronning, Filip; Analytis, James G.
2016-01-01
Electrons in materials with linear dispersion behave as massless Weyl- or Dirac-quasiparticles, and continue to intrigue due to their close resemblance to elusive ultra-relativistic particles as well as their potential for future electronics. Yet the experimental signatures of Weyl-fermions are often subtle and indirect, in particular if they coexist with conventional, massive quasiparticles. Here we show a pronounced anomaly in the magnetic torque of the Weyl semimetal NbAs upon entering the quantum limit state in high magnetic fields. The torque changes sign in the quantum limit, signalling a reversal of the magnetic anisotropy that can be directly attributed to the topological nature of the Weyl electrons. Our results establish that anomalous quantum limit torque measurements provide a direct experimental method to identify and distinguish Weyl and Dirac systems. PMID:27545105
Magnetic torque anomaly in the quantum limit of Weyl semimetals.
Moll, Philip J W; Potter, Andrew C; Nair, Nityan L; Ramshaw, B J; Modic, K A; Riggs, Scott; Zeng, Bin; Ghimire, Nirmal J; Bauer, Eric D; Kealhofer, Robert; Ronning, Filip; Analytis, James G
2016-01-01
Electrons in materials with linear dispersion behave as massless Weyl- or Dirac-quasiparticles, and continue to intrigue due to their close resemblance to elusive ultra-relativistic particles as well as their potential for future electronics. Yet the experimental signatures of Weyl-fermions are often subtle and indirect, in particular if they coexist with conventional, massive quasiparticles. Here we show a pronounced anomaly in the magnetic torque of the Weyl semimetal NbAs upon entering the quantum limit state in high magnetic fields. The torque changes sign in the quantum limit, signalling a reversal of the magnetic anisotropy that can be directly attributed to the topological nature of the Weyl electrons. Our results establish that anomalous quantum limit torque measurements provide a direct experimental method to identify and distinguish Weyl and Dirac systems. PMID:27545105
Some cosmological consequences of Weyl invariance
Alvarez, Enrique; González-Martín, Sergio; Herrero-Valea, Mario
2015-03-19
We examine some Weyl invariant cosmological models in the framework of generalized dilaton gravity, in which the action is made of a set of N conformally coupled scalar fields. It will be shown that when the FRW ansatz for the spacetime metric is assumed, the Ward identity for conformal invariance guarantees that the gravitational equations hold whenever the scalar fields EM do so. It follows that any scale factor can solve the theory provided a non-trivial profile for a dilaton field. In particular, accelerated expansion is a natural solution to the full set of equations.
Photovoltaic chiral magnetic effect in Weyl semimetals
NASA Astrophysics Data System (ADS)
Taguchi, Katsuhisa; Imaeda, Tatsushi; Sato, Masatoshi; Tanaka, Yukio
2016-05-01
We theoretically predict current generation in Weyl semimetals when circularly polarized light is applied. The electric field of the light can drive an effective magnetic field on the order of 10 T. For lower-frequency light, a nonequilibrium spin distribution is formed near the Fermi surface. Spin-momentum locking induces a giant electric current proportional to the effective magnetic field. In contrast, higher-frequency light realizes a quasistatic Floquet state with no induced electric current. We discuss the relevant materials and estimate the order of magnitude of the induced current.
The pointwise product in Weyl quantization
NASA Astrophysics Data System (ADS)
Dubin, D. A.; Hennings, M. A.
2004-07-01
We study the odot-product of Bracken [1], which is the Weyl quantized version of the pointwise product of functions in phase space. We prove that it is not compatible with the algebras of finite rank and Hilbert-Schmidt operators. By solving the linearization problem for the special Hermite functions, we are able to express the odot-product in terms of the component operators, mediated by the linearization coefficients. This is applied to finite rank operators and their matrices, and operators whose symbols are radial and angular distributions.
Constant, Philippe; Chowdhury, Soumitra Paul; Hesse, Laura; Pratscher, Jennifer; Conrad, Ralf
2011-01-01
Streptomyces soil isolates exhibiting the unique ability to oxidize atmospheric H2 possess genes specifying a putative high-affinity [NiFe]-hydrogenase. This study was undertaken to explore the taxonomic diversity and the ecological importance of this novel functional group. We propose to designate the genes encoding the small and large subunits of the putative high-affinity hydrogenase hhyS and hhyL, respectively. Genome data mining revealed that the hhyL gene is unevenly distributed in the phyla Actinobacteria, Proteobacteria, Chloroflexi, and Acidobacteria. The hhyL gene sequences comprised a phylogenetically distinct group, namely, the group 5 [NiFe]-hydrogenase genes. The presumptive high-affinity H2-oxidizing bacteria constituting group 5 were shown to possess a hydrogenase gene cluster, including the genes encoding auxiliary and structural components of the enzyme and four additional open reading frames (ORFs) of unknown function. A soil survey confirmed that both high-affinity H2 oxidation activity and the hhyL gene are ubiquitous. A quantitative PCR assay revealed that soil contained 106 to 108 hhyL gene copies g (dry weight)−1. Assuming one hhyL gene copy per genome, the abundance of presumptive high-affinity H2-oxidizing bacteria was higher than the maximal population size for which maintenance energy requirements would be fully supplied through the H2 oxidation activity measured in soil. Our data indicate that the abundance of the hhyL gene should not be taken as a reliable proxy for the uptake of atmospheric H2 by soil, because high-affinity H2 oxidation is a facultatively mixotrophic metabolism, and microorganisms harboring a nonfunctional group 5 [NiFe]-hydrogenase may occur. PMID:21742924
NASA Astrophysics Data System (ADS)
Dodd, R. K.
2014-02-01
In this paper we derive Hirota equations associated with the simply laced affine Lie algebras {{g}}^{(1)}, where {{g}} is one of the simply laced complex Lie algebras {{a}}_n, {{d}}_n, {{e}}_6, {{e}}_7 or {{e}}_8, defined by finite order automorphisms of {{g}} which we call Lepowsky automorphisms. In particular, we investigate the Hirota equations for Lepowsky automorphisms of {{e}}_6 defined by the cuspidal class E6 of the Weyl group W(E6) of {{e}}_6. We also investigate the relationship between the Lepowsky automorphisms of the simply laced complex Lie algebras {{g}} and the conjugate canonical automorphisms defined by Kac. This analysis is applied to identify the canonical automorphisms for the cuspidal class E6 of {{e}}_6.
NASA Astrophysics Data System (ADS)
Qian, Jin; Skyllberg, Ulf; Frech, Wolfgang; Bleam, William F.; Bloom, Paul R.; Petit, Pierre Emmanuel
2002-11-01
We combined synchrotron-based X-ray absorption near edge structure (XANES) spectroscopy, extended X-ray absorption fine structure (EXAFS) spectroscopy and binding affinity studies to determine the coordination, geometry, and strength of methyl mercury, CH 3Hg (II), bonding in soil and stream organic matter. Samples of organic soil (OS), potentially soluble organic substances (PSOS) from the soil, and organic substances from a stream (SOS) draining the soil were taken along a short "hydrological transect." We determined the sum of concentrations of highly reduced organic S groups (designated Org-S RED), such as thiol (RSH), disulfane (RSSH), sulfide (RSR), and disulfide (RSSR), using sulfur K-edge XANES. Org-S RED varied between 27% and 64% of total S in our samples. Hg LIII-edge EXAFS analysis were determined on samples added CH 3Hg (II) to yield CH 3Hg (II)/Org-S RED ratios in the range 0.01-1.62. At low ratios, Hg was associated to one C atom (the methyl group) at an average distance of 2.03 ± 0.02 Å and to one S atom at an average distance of 2.34 ± 0.03 Å, in the first coordination shell. At calculated CH 3Hg(II)/Org-S RED ratios above 0.37 in OS, 0.32 in PSOS, and 0.24 in SOS, the organic S sites were saturated by CH 3Hg +, and O (and/or N) atoms were found in the first coordination shell of Hg at an average distance of 2.09 ± 0.01 Å. Based on the assumption that RSH (and possibly RSSH) groups take part in the complexation of CH 3Hg +, whereas RSSR and RSR groups do not, approximately 17% of total organic S consisted of RSH (+ RSSH) functionalities in the organic soil. Corresponding figures for samples PSOS and SOS were 14% and 9%, respectively. Competitive complexation of CH 3Hg + by halide ions was used to determine the average binding strength of native concentrations of CH 3Hg (II) in the OS sample. Using data for Org-S RED, calculated surface complexation constants were in the range from 10 16.3 to 10 16.7 for a model RSH site having an acidity
Two-parameter asymptotics in magnetic Weyl calculus
NASA Astrophysics Data System (ADS)
Lein, Max
2010-12-01
This paper is concerned with small parameter asymptotics of magnetic quantum systems. In addition to a semiclassical parameter ɛ, the case of small coupling λ to the magnetic vector potential naturally occurs in this context. Magnetic Weyl calculus is adapted to incorporate both parameters, at least one of which needs to be small. Of particular interest is the expansion of the Weyl product which can be used to expand the product of operators in a small parameter, a technique which is prominent to obtain perturbation expansions. Three asymptotic expansions for the magnetic Weyl product of two Hörmander class symbols are proven as (i) ɛ ≪ 1 and λ ≪ 1, (ii) ɛ ≪ 1 and λ = 1, as well as (iii) ɛ = 1 and λ ≪ 1. Expansions (i) and (iii) are impossible to obtain with ordinary Weyl calculus. Furthermore, I relate the results derived by ordinary Weyl calculus with those obtained with magnetic Weyl calculus by one- and two-parameter expansions. To show the power and versatility of magnetic Weyl calculus, I derive the semirelativistic Pauli equation as a scaling limit from the Dirac equation up to errors of fourth order in 1/c.
Landau levels and longitudinal magnetoresistance in generalized Weyl semimetals
NASA Astrophysics Data System (ADS)
Li, Xiao; Roy, Bitan
The notion of axial anomaly is a venerable concept in quantum field theory that has received ample attention in condensed matter physics due to the discovery of Weyl materials (WSMs). In such systems Kramers non-degenerate bands touch at isolated points in the Brillouin zone that act as (anti)monopoles of Berry flux, and the monopole number (m) defines the topological invariant of the system. Although so far only simple WSMs (with m = 1) has been found in various inversion and/or time-reversal asymmetric systems, generalized Weyl semimetals with m > 1 can also be found in nature, for example double-Weyl semimetals in HgCr2Se4 and SrSi2 and triple-Weyl semimetals. In this work, we demonstrate the Landau level spectrum in generalized Weyl systems and its ramification on longitudinal magnetotransport measurements. We show that in the quantum limit generalized Weyl semimetals display negative longitudinal magnetoresistance due to the chiral anomaly. Moreover, the magnetoresistance has nontrivial dependence on the relative orientation of the external fields with the crystallographic axis, stemming from underlying anisotropic quasiparticle dispersion in the pristine system. Our theory can thus provide diagnostic tools to pin the quasiparticle properties in Weyl systems.
Two-parameter asymptotics in magnetic Weyl calculus
Lein, Max
2010-12-15
This paper is concerned with small parameter asymptotics of magnetic quantum systems. In addition to a semiclassical parameter {epsilon}, the case of small coupling {lambda} to the magnetic vector potential naturally occurs in this context. Magnetic Weyl calculus is adapted to incorporate both parameters, at least one of which needs to be small. Of particular interest is the expansion of the Weyl product which can be used to expand the product of operators in a small parameter, a technique which is prominent to obtain perturbation expansions. Three asymptotic expansions for the magnetic Weyl product of two Hoermander class symbols are proven as (i) {epsilon}<< 1 and {lambda}<< 1, (ii) {epsilon}<< 1 and {lambda}= 1, as well as (iii) {epsilon}= 1 and {lambda}<< 1. Expansions (i) and (iii) are impossible to obtain with ordinary Weyl calculus. Furthermore, I relate the results derived by ordinary Weyl calculus with those obtained with magnetic Weyl calculus by one- and two-parameter expansions. To show the power and versatility of magnetic Weyl calculus, I derive the semirelativistic Pauli equation as a scaling limit from the Dirac equation up to errors of fourth order in 1/c.
NASA Astrophysics Data System (ADS)
Ren, Gang; Du, Jian-Ming
2012-06-01
Based on the technique of integration with a Weyl ordered product (IWWOP) for the two-mode operator, we derive out the Weyl ordered form of two-mode Fresnel operator (TFO). The multiplication rule for TFO and the matrix element of Weyl ordered form of TFO in coordinate eigenstates are also discussed.
A Heisenberg Algebra Bundle of a Vector Field in Three-Space and its Weyl Quantization
Binz, Ernst; Pods, Sonja
2006-01-04
In these notes we associate a natural Heisenberg group bundle Ha with a singularity free smooth vector field X = (id,a) on a submanifold M in a Euclidean three-space. This bundle yields naturally an infinite dimensional Heisenberg group H{sub X}{sup {infinity}}. A representation of the C*-group algebra of H{sub X}{sup {infinity}} is a quantization. It causes a natural Weyl-deformation quantization of X. The influence of the topological structure of M on this quantization is encoded in the Chern class of a canonical complex line bundle inside Ha.
Conformal Weyl Gravity and Perihelion Precession
NASA Technical Reports Server (NTRS)
Sultana, Joseph; Kazanas, Demosthenes; Said, Jakson, Levi
2012-01-01
We investigate the perihelion shift of planetary motion in conformal Weyl gravity using the metric of the static, spherically symmetric solution discovered by Mannheim and Kazanas. To this end we employ a procedure similar to that used by Weinberg for the Schwarzschild solution, which has also been used recently to study the solar system effects of the cosmological constant Lambda. We show that besides the general relativistic terms obtained earlier from the Schwarzschild-de Sitter solution, the expression for the perihelion shift includes a negative contribution which arises from the linear term gamma ray in the metric. Using data for perihelion shift observations, we obtain constraints on the value of the constant gammma similar to that obtained earlier using galactic rotational curves.
Massive mesons in Weyl-Dirac theory
NASA Astrophysics Data System (ADS)
Mirabotalebi, S.; Ahmadi, F.; Salehi, H.
2008-01-01
In order to study the mass generation of the vector fields in the framework of a conformal invariant gravitational model, the Weyl-Dirac theory is considered. The mass of the Weyl’s meson fields plays a principal role in this theory, it connects basically the conformal and gauge symmetries. We estimate this mass by using the large-scale characteristics of the observed universe. To do this we firstly specify a preferred conformal frame as a cosmological frame, then in this frame, we introduce an exact possible solution of the theory. We also study the dynamical effect of the massive vector meson fields on the trajectories of an elementary particle. We show that a local change of the cosmological frame leads to a Hamilton-Jacobi equation describing a particle with an adjustable mass. The dynamical effect of the massive vector meson field presents itself in the form of a correction term for the mass of the particle.
Bending of light in conformal Weyl gravity
NASA Astrophysics Data System (ADS)
Sultana, Joseph; Kazanas, Demosthenes
2010-06-01
We reexamine the bending of light issue associated with the metric of the static, spherically symmetric solution of Weyl gravity discovered by Mannheim and Kazanas (1989). To this end we employ the procedure used recently by Rindler and Ishak to obtain the bending angle of light by a centrally concentrated spherically symmetric matter distribution in a Schwarzschild-de Sitter background. In earlier studies the term γr in the metric led to the paradoxical result of a bending angle proportional to the photon impact parameter, when using the usual formalism appropriate to asymptotically flat space-times. However, employing the approach of light bending of Rindler and Ishak we show that the effects of this term are in fact insignificant, with the discrepancy between the two procedures attributed to the definition of the bending angle between the asymptotically flat and nonflat spaces.
Optical spectroscopy study of Weyl Semimetal NbP
NASA Astrophysics Data System (ADS)
Yang, Jeremy; Jiang, Yuxuan; Dun, Zhiling; Zhou, Haidong; Smirnov, Dmitry; Jiang, Zhigang
Weyl semimetals have attracted much interest lately because of its unique band structure, where conduction band and valence band touch at discrete points. Here, we report on optical spectroscopy study of Weyl semimetal NbP, seeking evidence for the existence of Weyl fermions. Specifically, using Raman spectroscopy we investigate the anisotropic response of Raman-active phonon modes in NbP and compare with Quantum Espresso simulations. Using magneto-infrared spectroscopy in a high magnetic field up to 17.5T, we observe several Landau level transitions and compare with the theoretical model of three-dimensional massless Dirac/Weyl fermions. By combining our data with low-temperature magneto-transport measurement, the magnetic field dispersion of Landau levels in NbP is obtained.
FLRW cosmology in Weyl-integrable space-time
Gannouji, Radouane; Nandan, Hemwati; Dadhich, Naresh E-mail: hntheory@yahoo.co.in
2011-11-01
We investigate the Weyl space-time extension of general relativity (GR) for studying the FLRW cosmology through focusing and defocusing of the geodesic congruences. We have derived the equations of evolution for expansion, shear and rotation in the Weyl space-time. In particular, we consider the Starobinsky modification, f(R) = R+βR{sup 2}−2Λ, of gravity in the Einstein-Palatini formalism, which turns out to reduce to the Weyl integrable space-time (WIST) with the Weyl vector being a gradient. The modified Raychaudhuri equation takes the form of the Hill-type equation which is then analysed to study the formation of the caustics. In this model, it is possible to have a Big Bang singularity free cyclic Universe but unfortunately the periodicity turns out to be extremely short.
Weyl Superfluidity in a Three-dimensional Dipolar Fermi Gas
NASA Astrophysics Data System (ADS)
Liu, Bo; Li, Xiaopeng; Yin, Lan; Liu, W. Vincent
2015-03-01
Weyl superconductivity or superfluidity, a fascinating topological state of matter, features novel phenomena such as emergent Weyl fermionic excitations and anomalies. Here we report that an anisotropic Weyl superfluid state can arise as a low temperature stable phase in a 3D dipolar Fermi gas. A crucial ingredient of our model is a direction-dependent two-body effective attraction generated by a rotating external field. Experimental signatures are predicted for cold gases in radio-frequency spectroscopy. The finite temperature phase diagram of this system is studied and the transition temperature of the Weyl superfluidity is found to be within the experimental scope for atomic dipolar Fermi gases. Work supported in part by U.S. ARO, AFOSR, DARPA-OLE-ARO, Charles E. Kaufman Foundation and The Pittsburgh Foundation, JQI-NSF-PFC, ARO-Atomtronics-MURI, and NSF of China.
Weyl holographic superconductor in the Lifshitz black hole background
NASA Astrophysics Data System (ADS)
Mansoori, S. A. Hosseini; Mirza, B.; Mokhtari, A.; Dezaki, F. Lalehgani; Sherkatghanad, Z.
2016-07-01
We investigate analytically the properties of the Weyl holographic superconductor in the Lifshitz black hole background. We find that the critical temperature of the Weyl superconductor decreases with increasing Lifshitz dynamical exponent, z, indicating that condensation becomes difficult. In addition, it is found that the critical temperature and condensation operator could be affected by applying the Weyl coupling, γ. Moreover, we compute the critical magnetic field and investigate its dependence on the parameters γ and z. Finally, we show numerically that the Weyl coupling parameter γ and the Lifshitz dynamical exponent z together control the size and strength of the conductivity peak and the ratio of gap frequency over critical temperature ω g /T c .
RKKY interaction of magnetic impurities in Dirac and Weyl semimetals
NASA Astrophysics Data System (ADS)
Chang, Hao-Ran; Zhou, Jianhui; Wang, Shi-Xiong; Shan, Wen-Yu; Xiao, Di
2015-12-01
We theoretically study the Ruderman-Kittel-Kasuya-Yosida (RKKY) interaction between magnetic impurities in both Dirac and Weyl semimetals (SMs). We find that the internode process, as well as the unique three-dimensional spin-momentum locking, has significant influences on the RKKY interaction, resulting in both a Heisenberg and an Ising term, and an additional Dzyaloshinsky-Moriya term if the inversion symmetry is absent. These interactions can lead to rich spin textures and possible ferromagnetism in Dirac and time-reversal symmetry-invariant Weyl SMs. The effect of anisotropic Dirac and Weyl nodes on the RKKY interaction is also discussed. Our results provide an alternative scheme to engineer topological SMs and shed new light on the application of Dirac and Weyl SMs in spintronics.
Emergent Weyl excitations in systems of polar particles
NASA Astrophysics Data System (ADS)
Syzranov, Sergey; Wall, Michael; Zhu, Bihui; Gurarie, Victor; Rey, Ana Maria
2016-05-01
Systems with Weyl quasiparticle dispersion have been predicted to display a plethora of novel fascinating phenomena: chiral anomaly, topologically protected Fermi arcs on the surfaces, non-Anderson disorder-driven transitions, etc. Over the last several years enormous research efforts have been directed at finding new Weyl semimetals in solid-state systems and ways to realise them in ultracold atomic gases. We demonstrate that excitations with Weyl dispersion generically exist in three-dimensional systems of polar particles in the presence of magnetic field. They emerge due to the dipolar-interaction-induced transitions between the J = 0 and J = 1 angular-momentum states of the particles. Also, we calculate the quasiparticle spectra microscopically for systems of alkaline-earth atoms that can be realised experimentally and suggest a Ramsey-spectroscopy protocol for observing Weyl excitations in them.
Structured Weyl Points in Spin-Orbit Coupled Fermionic Superfluids
NASA Astrophysics Data System (ADS)
Xu, Yong; Zhang, Fan; Zhang, Chuanwei
2015-12-01
We demonstrate that a Weyl point, widely examined in 3D Weyl semimetals and superfluids, can develop a pair of nondegenerate gapless spheres. Such a bouquet of two spheres is characterized by three distinct topological invariants of manifolds with full energy gaps, i.e., the Chern number of a 0D point inside one developed sphere, the winding number of a 1D loop around the original Weyl point, and the Chern number of a 2D surface enclosing the whole bouquet. We show that such structured Weyl points can be realized in the superfluid quasiparticle spectrum of a 3D degenerate Fermi gas subject to spin-orbit couplings and Zeeman fields, which supports Fulde-Ferrell superfluids as the ground state.
Weyl Node and Spin Texture in Trigonal Tellurium and Selenium
NASA Astrophysics Data System (ADS)
Hirayama, Motoaki; Okugawa, Ryo; Ishibashi, Shoji; Murakami, Shuichi; Miyake, Takashi
2015-05-01
We study Weyl nodes in materials with broken inversion symmetry. We find based on first-principles calculations that trigonal Te and Se have multiple Weyl nodes near the Fermi level. The conduction bands have a spin splitting similar to the Rashba splitting around the H points, but unlike the Rashba splitting the spin directions are radial, forming a hedgehog spin texture around the H points, with a nonzero Pontryagin index for each spin-split conduction band. The Weyl semimetal phase, which has never been observed in real materials without inversion symmetry, is realized under pressure. The evolution of the spin texture by varying the pressure can be explained by the evolution of the Weyl nodes in k space.
Ruderman-Kittel-Kasuya-Yosida interaction in Weyl semimetals
NASA Astrophysics Data System (ADS)
Hosseini, Mir Vahid; Askari, Mehdi
2015-12-01
We theoretically demonstrate the Ruderman-Kittel-Kasuya-Yosida interaction between magnetic impurities that is mediated by the Weyl fermions embedded inside a three-dimensional Weyl semimetal (WSM). The WSM is characterized by a pair of Weyl points separated in the momentum space. Using the Green's function method and a two-band model, we show that four terms contribute to the magnetic impurity interaction in the WSM phase: the Heisenberg, Dzyaloshinsky-Moriya, spin-frustrated, and Ising terms. Except for the last term which is vanishingly small in the plane perpendicular to the line connecting two Weyl points, all the other interaction terms are finite. Furthermore, the magnetic spins of the Dzyaloshinsky-Moriya and spin-frustrated terms lie in the plane perpendicular to the line connecting two Weyl points, but in this plane, the magnetic spins of the Ising term have no components. For each contribution, an analytical expression is obtained, falling off with a spatial dependence as R-5 at Weyl points and showing beating behavior that depends on the direction between two magnetic impurities.
Linear magnetoconductivity in an intrinsic topological Weyl semimetal
NASA Astrophysics Data System (ADS)
Zhang, Song-Bo; Lu, Hai-Zhou; Shen, Shun-Qing
2016-05-01
Searching for the signature of the violation of chiral charge conservation in solids has inspired a growing passion for the magneto-transport in topological semimetals. One of the open questions is how the conductivity depends on magnetic fields in a semimetal phase when the Fermi energy crosses the Weyl nodes. Here, we study both the longitudinal and transverse magnetoconductivity of a topological Weyl semimetal near the Weyl nodes with the help of a two-node model that includes all the topological semimetal properties. In the semimetal phase, the Fermi energy crosses only the 0th Landau bands in magnetic fields. For a finite potential range of impurities, it is found that both the longitudinal and transverse magnetoconductivity are positive and linear at the Weyl nodes, leading to an anisotropic and negative magnetoresistivity. The longitudinal magnetoconductivity depends on the potential range of impurities. The longitudinal conductivity remains finite at zero field, even though the density of states vanishes at the Weyl nodes. This work establishes a relation between the linear magnetoconductivity and the intrinsic topological Weyl semimetal phase.
Thermo-electric transports in double-Weyl semimetals
NASA Astrophysics Data System (ADS)
Chen, Qi; Fiete, Gregory A.
Topological Weyl semimetals with linearly dispersing nodal points have received a surge of interest due to their experimental realization in real materials. Another nontrivial type of band crossing whose dispersion is not simply linear is the double Weyl point, around which the spectrum disperses linearly along one momentum direction but quadratically along the two remaining directions. In this work, we apply the semi-classical Boltzmann transport theory to study the thermo-electric conductivity of a double-Weyl fermion model. We find that the transport quantities exhibit an interesting dependence on the chemical potential and spatial anisotropic model parameters, differing from a simple quadratically or linearly dispersing electron gas. By applying a static magnetic field, we find that the double-Weyl point is only stable for a magnetic field along the linearly dispersing direction. The longitudinal and transverse electrical and thermal magneto-conductivity show a similar dependence on the in-plane cyclotron frequency to the linearly dispersing Weyl nodes. In the extreme quantum limit of chemical potential being much smaller than the cyclotron energy, we find that the lowest Landau levels are both chiral and doubly degenerate. The chiral anomaly contribution to the longitudinal magneto-conductivity is double that of a linearly dispersing Weyl node.
Chiral nodes and oscillations in the Josephson current in Weyl semimetals
NASA Astrophysics Data System (ADS)
Khanna, Udit; Mukherjee, Dibya Kanti; Kundu, Arijit; Rao, Sumathi
2016-03-01
The separation of the Weyl nodes in a broken time-reversal symmetric Weyl semimetal leads to helical quasiparticle excitations at the Weyl nodes which, when coupled with overall spin conservation, allows only internodal transport at the junction of the Weyl semimetal with a superconductor. This leads to an unusual periodic oscillation in the Josephson current as a function of k0L , where L is the length of the Weyl semimetal and 2 k0 is the internodal distance. This oscillation is robust and should be experimentally measurable, providing a direct path to confirming the existence of chiral nodes in the Weyl semimetal.
Spinors, gravity and recalibration invariance. Microphysical motivation for the weyl geometry
NASA Astrophysics Data System (ADS)
Sławianowski, Jan J.
1995-02-01
Discussed is the status of scale and internal geometry in the theory of mutually interacting gravitational and spinor fields. Suggested is a class of dynamical models free of any introduced by hand scale standards, absolute objects, etc. in internal spaces of field multiplets. Weyl geometry of the physical space-time seems to be implied by the Finkelstein-Penrose-Weizsäcker idea [2,12] about two-component complex objects which describe an ultimate physical reality, underlying quantum phenomena and spatio-temporal structures. There are certain links with the Hehl's idea of dilaton [7] and the metric-affine gravitation theory. Our analysis seems to suggest that some short-range massive modes may appear in the gravitational sector of field quantities.
Report: Affinity Chromatography.
ERIC Educational Resources Information Center
Walters, Rodney R.
1985-01-01
Supports, affinity ligands, immobilization, elution methods, and a number of applications are among the topics considered in this discussion of affinity chromatography. An outline of the basic principles of affinity chromatography is included. (JN)
Weyl, Dirac and Maxwell Quantum Cellular Automata
NASA Astrophysics Data System (ADS)
Bisio, Alessandro; D'Ariano, Giacomo Mauro; Perinotti, Paolo; Tosini, Alessandro
2015-10-01
Recent advances on quantum foundations achieved the derivation of free quantum field theory from general principles, without referring to mechanical notions and relativistic invariance. From the aforementioned principles a quantum cellular automata (QCA) theory follows, whose relativistic limit of small wave-vector provides the free dynamics of quantum field theory. The QCA theory can be regarded as an extended quantum field theory that describes in a unified way all scales ranging from an hypothetical discrete Planck scale up to the usual Fermi scale. The present paper reviews the automaton theory for the Weyl field, and the composite automata for Dirac and Maxwell fields. We then give a simple analysis of the dynamics in the momentum space in terms of a dispersive differential equation for narrowband wave-packets. We then review the phenomenology of the free-field automaton and consider possible visible effects arising from the discreteness of the framework. We conclude introducing the consequences of the automaton dispersion relation, leading to a deformed Lorentz covariance and to possible effects on the thermodynamics of ideal gases.
Surface states of massive Dirac fermions with separated Weyl nodes
NASA Astrophysics Data System (ADS)
Buividovich, P. V.
2016-01-01
We derive the spectra of surface states for massive Dirac Hamiltonians with either momentum or energy separation between the left- and right-handed Weyl nodes. Momentum separation between the Weyl nodes corresponds to the explicitly broken time-reversal symmetry and the energy separation - to broken parity. Such Hamiltonians provide the simplest model description of Weyl semimetals. We find that the only effect of the energy separation between the Weyl nodes is to decrease the Fermi velocity in the linear dispersion relation of the surface states of massive Dirac Hamiltonian. In the case of broken time-reversal symmetry, the spectrum of surface states interpolates in a nontrivial way between the Fermi arc-type and the Dirac cone-type dispersion relations. In particular we find that for all values of the mass and the momentum separation between the Weyl nodes the surface states only exist in a strip of finite width in momentum space. We give also some simpler examples of surface states in order to make these notes more pedagogical.
Negative longitudinal magnetoresistance in Dirac and Weyl metals
NASA Astrophysics Data System (ADS)
Burkov, A. A.
2015-06-01
It has recently been found that Dirac and Weyl metals are characterized by an unusual weak-field longitudinal magnetoresistance: large, negative, and quadratic in the magnetic field. This has been shown to arise from the chiral anomaly, i.e., nonconservation of the chiral charge in the presence of external electric and magnetic fields, oriented collinearly. In this paper we report on a theory of this effect in both Dirac and Weyl metals. We demonstrate that this phenomenon contains two important ingredients. One is the magnetic-field-induced coupling between the chiral and the total (or vector, in relativistic field theory terminology) charge densities. This arises from the Berry curvature and is present in principle whenever the Berry curvature is nonzero, i.e., is nonspecific to Dirac and Weyl metals. This coupling, however, leads to a large negative quadratic magnetoresistance only when the second ingredient is present, namely when the chiral charge density is a nearly conserved quantity with a long relaxation time. This property is specific to Dirac and Weyl metals and is realized only when the Fermi energy is close to Dirac or Weyl nodes, expressing an important low-energy property of these materials, emergent chiral symmetry.
Disorder and Metal-Insulator Transitions in Weyl Semimetals.
Chen, Chui-Zhen; Song, Juntao; Jiang, Hua; Sun, Qing-feng; Wang, Ziqiang; Xie, X C
2015-12-11
The Weyl semimetal (WSM) is a newly proposed quantum state of matter. It has Weyl nodes in bulk excitations and Fermi arc surface states. We study the effects of disorder and localization in WSMs and find three novel phase transitions. (i) Two Weyl nodes near the Brillouin zone boundary can be annihilated pairwise by disorder scattering, resulting in the opening of a topologically nontrivial gap and a transition from a WSM to a three-dimensional quantum anomalous Hall state. (ii) When the two Weyl nodes are well separated in momentum space, the emergent bulk extended states can give rise to a direct transition from a WSM to a 3D diffusive anomalous Hall metal. (iii) Two Weyl nodes can emerge near the zone center when an insulating gap closes with increasing disorder, enabling a direct transition from a normal band insulator to a WSM. We determine the phase diagram by numerically computing the localization length and the Hall conductivity, and propose that the novel phase transitions can be realized on a photonic lattice. PMID:26705648
Ling, Yan; Wang, Chun-You; Yang, Zhi-Yong
2009-11-01
To investigate the affinity constants of heparin with high mobility group protein 1(HMGB1) and HMGB1 with the receptor of advanced glycation end products (RAGE) and to analyze the impact of heparin on the affinity of HMGB1 and RAGE, the standard BIAcore amine coupling chemistry protocol using EDC and NHS was employed for immobilizing. Surface plasmon resonance biosensor technology was used to detect the affinity constants of heparin/HMGB1, HMGB1/RAGE and heparin/ RAGE. Binding analysis was used to investigate the impact of heparin on the affinity of HMGB1 and RAGE. After the immobilization, 9 000 and 5 000 RU rise of HMGB1 and RAGE respectively were obtained. These meant that the immobilized values of HMGB1 and RAGE were about 9 and 5 ng x mm(-2) respectively. The kinetic constants were k(a) = 1.78 x 10(5) L x mol(-1) x s(-1), kd = 8.02 x 10(-4) s(-1), and the affinity constants were KA = 2.22 x 10(8) L x mol(-1), the equilibrium dissociation constant K(D) = 4.5 x 10(-9) mol x L(-1) for heparin and HMGB1; while the kinetic constants were k(a) = 1.85 x 10(3) L x mol(-1) x s(-1), k(d) = 1.81 x 10(-4) s(-1), K(A) = 1.02 x 10(7) L x mol(-1), K(D) = 9.77 x 10(-8) mol x L(-1) for HMGB1 and RAGE; there was very low affinity of heparin with RAGE. The highest concentration of 10 000 u x L(-1) of heparin in this experiment did not reach the saturation with HMGB1. After 50 mg x L(-1) of HMGB1 was mixed with heparin of 50, 100, 1 000, 10 000 u x L(-1), the combining amount of HMGB1 and RAGE declined from 100 to 50 RU. But there were no significant differences between different concentrations of heparin. It was concluded that heparin can combine with HMGB1 and affect the affinity of HMGB1/RAGE. In addition, this impact was not in a dose-dependent manner. PMID:20101991
Anomalous Weyl superfluid in three-dimensional ultracold fermionic gases
NASA Astrophysics Data System (ADS)
Huang, Beibing
2016-08-01
In this paper we use layer construction method to construct an experimentally feasible model to realize one type of anomalous Weyl superfluids (WS) in the context of cold fermionic gases. This exotic phase still characterizes the Weyl points in the bulk but completely different Majorana Fermi arc surface state (MFASS) on the boundaries. In contrast to conventional WS, where MFASS only connects the projection of Weyl points, new MFASS continuously stretches to the border of surface Brillouin zone. We self-consistently determine the phase diagram of model at the mean-field level to claim the achievement of anomalous WS. In addition, inversion symmetry and band inversion in this model are analyzed in detail to provide unique feature of identifying anomalous WS experimentally by momentum-resolved radio-frequency spectroscopy.
Topological Imbert-Fedorov Shift in Weyl Semimetals
NASA Astrophysics Data System (ADS)
Jiang, Qing-Dong; Jiang, Hua; Liu, Haiwen; Sun, Qing-Feng; Xie, Xin-Cheng
The Goos-Hänchen (GH) shift and the Imbert-Fedorov (IF) shift are optical phenomena which describe the longitudinal and transverse lateral shifts at the reflection interface, respectively. Here, we predict the GHIF shifts in Weyl semimetals (WSMs)--a promising material harboring low energy Weyl fermions, afermionic cousin of photons. Our results show that the GH shift in WSMs is valley independent,is analogous to that discovered in a 2D relativistic material--graphene. However, the IF shift hasbeen explored in nonoptical systems, and here we show that it is valley dependent. Furthermore, wethat the IF shift actually originates from the topological effect of the system. Experimentally, theIF shift can be utilized to characterize theWeyl semimetals, design valleytronic devices of high, and measure the Berry curvature. Morever, we investigate the transport properties of topological semimetal using the wave-packet dynamics, which give some interesting results. NBRP of China, NSF-China.
Topological Imbert-Fedorov Shift in Weyl Semimetals
NASA Astrophysics Data System (ADS)
Jiang, Qing-Dong; Jiang, Hua; Liu, Haiwen; Sun, Qing-Feng; Xie, X. C.
2015-10-01
The Goos-Hänchen (GH) shift and the Imbert-Fedorov (IF) shift are optical phenomena which describe the longitudinal and transverse lateral shifts at the reflection interface, respectively. Here, we predict the GH and IF shifts in Weyl semimetals (WSMs)—a promising material harboring low energy Weyl fermions, a massless fermionic cousin of photons. Our results show that the GH shift in WSMs is valley independent, which is analogous to that discovered in a 2D relativistic material—graphene. However, the IF shift has never been explored in nonoptical systems, and here we show that it is valley dependent. Furthermore, we find that the IF shift actually originates from the topological effect of the system. Experimentally, the topological IF shift can be utilized to characterize the Weyl semimetals, design valleytronic devices of high efficiency, and measure the Berry curvature.
Weyl and Dirac semimetals with Z2 topological charge
NASA Astrophysics Data System (ADS)
Morimoto, Takahiro; Furusaki, Akira
2014-06-01
We study the stability of gap-closing (Weyl or Dirac) points in the three-dimensional Brillouin zone of semimetals using Clifford algebras and their representation theory. We show that a pair of Weyl points with Z2 topological charge are stable in a semimetal with time-reversal and reflection symmetries when the square of the product of the two symmetry transformations equals minus identity. We present toy models of Z2 Weyl semimetals which have surface modes forming helical Fermi arcs. We also show that Dirac points with Z2 topological charge are stable in a semimetal with time-reversal, inversion, and SU(2) spin rotation symmetries when the square of the product of time-reversal and inversion equals plus identity. Furthermore, we briefly discuss the topological stability of point nodes in superconductors using Clifford algebras.
Weyl's Raum, Zeit, Materie and its Early Reception
NASA Astrophysics Data System (ADS)
Eckes, Christophe
2015-01-01
Let us recall first some biographical data. Hermann Weyl (1885-1955) becomes professor at the ETH (Zürich) in 1913. At that time, he is well known for his contributions in pure mathematics: Riemann surfaces and integral equations. Already in his works on integral equations -- especially in 1912-1913 -- he has strong interest in mathematical physics. Weyl's career is almost immediately interrupted by the First World War. According to Thomas Hawkins "Although at first Weyl was judged physically unfit for military service by the German army, he was finally drafted in the spring of 1915 but was discharged the following spring at the request of the Swiss government." His scientific career begins anew in 1916. During the period 1916-1923, his research is mainly devoted to the formalization of special and general relativity...
Optical spectroscopy of the Weyl semimetal TaAs
Xu, B.; Dai, Y. M.; Zhao, L. X.; Wang, K.; Yang, R.; Zhang, W.; Liu, J. Y.; Xiao, H.; Chen, G. F.; Taylor, A. J.; et al
2016-03-24
Here, we present a systematic study of both the temperature and frequency dependence of the optical response in TaAs, a material that has recently been realized to host the Weyl semimetal state. Our study reveals that the optical conductivity of TaAs features a narrow Drude response alongside a conspicuous linear dependence on frequency. The weight of the Drude peak decreases upon cooling, following a T2 temperature dependence, in good agreement with theoretical predictions. Two linear components with distinct slopes dominate the low-temperature optical conductivity. A comparison between our experimental results and theoretical calculations suggests that the linear conductivity below ~230more » cm–1 arises purely from interband transitions near the Weyl points, providing rich information about the Weyl semimetal state in TaAs.« less
P T -invariant Weyl semimetals in gauge-symmetric systems
NASA Astrophysics Data System (ADS)
Lepori, L.; Fulga, I. C.; Trombettoni, A.; Burrello, M.
2016-08-01
Weyl semimetals typically appear in systems in which either time-reversal (T ) or inversion (P ) symmetry is broken. Here we show that in the presence of gauge potentials these topological states of matter can also arise in fermionic lattices preserving both T and P . We analyze in detail the case of a cubic lattice model with π fluxes, discussing the role of gauge symmetries in the formation of Weyl points and the difference between the physical and the canonical T and P symmetries. We examine the robustness of this P T -invariant Weyl semimetal phase against perturbations that remove the chiral sublattice symmetries, and we discuss further generalizations. Finally, motivated by advances in ultracold-atom experiments and by the possibility of using synthetic magnetic fields, we study the effect of random perturbations of the magnetic fluxes, which can be compared to a local disorder in realistic scenarios.
Optical spectroscopy of the Weyl semimetal TaAs
NASA Astrophysics Data System (ADS)
Xu, B.; Dai, Y. M.; Zhao, L. X.; Wang, K.; Yang, R.; Zhang, W.; Liu, J. Y.; Xiao, H.; Chen, G. F.; Taylor, A. J.; Yarotski, D. A.; Prasankumar, R. P.; Qiu, X. G.
2016-03-01
We present a systematic study of both the temperature and frequency dependence of the optical response in TaAs, a material that has recently been realized to host the Weyl semimetal state. Our study reveals that the optical conductivity of TaAs features a narrow Drude response alongside a conspicuous linear dependence on frequency. The weight of the Drude peak decreases upon cooling, following a T2 temperature dependence, in good agreement with theoretical predictions. Two linear components with distinct slopes dominate the low-temperature optical conductivity. A comparison between our experimental results and theoretical calculations suggests that the linear conductivity below ˜230 cm-1 arises purely from interband transitions near the Weyl points, providing rich information about the Weyl semimetal state in TaAs.
Predicted Unusual Magnetoresponse in Type-II Weyl Semimetals
NASA Astrophysics Data System (ADS)
Yu, Zhi-Ming; Yao, Yugui; Yang, Shengyuan A.
2016-08-01
We show several distinct signatures in the magnetoresponse of type-II Weyl semimetals. The energy tilt tends to squeeze the Landau levels (LLs), and, for a type-II Weyl node, there always exists a critical angle between the B field and the tilt, at which the LL spectrum collapses, regardless of the field strength. Before the collapse, signatures also appear in the magneto-optical spectrum, including the invariable presence of intraband peaks, the absence of absorption tails, and the special anisotropic field dependence.
Predicted Unusual Magnetoresponse in Type-II Weyl Semimetals.
Yu, Zhi-Ming; Yao, Yugui; Yang, Shengyuan A
2016-08-12
We show several distinct signatures in the magnetoresponse of type-II Weyl semimetals. The energy tilt tends to squeeze the Landau levels (LLs), and, for a type-II Weyl node, there always exists a critical angle between the B field and the tilt, at which the LL spectrum collapses, regardless of the field strength. Before the collapse, signatures also appear in the magneto-optical spectrum, including the invariable presence of intraband peaks, the absence of absorption tails, and the special anisotropic field dependence. PMID:27563994
Thermodynamics, phase transition and quasinormal modes with Weyl corrections
NASA Astrophysics Data System (ADS)
Mahapatra, Subhash
2016-04-01
We study charged black holes in D dimensional AdS space, in the presence of four derivative Weyl correction. We obtain the black hole solution perturbatively up to first as well as second order in the Weyl coupling, and show that first law of black hole thermodynamics is satisfied in all dimensions. We study its thermodynamic phase transition and then calculate the quasinormal frequencies of the massless scalar field perturbation. We find that, here too, the quasinormal frequencies capture the essence of black hole phase transition. Few subtleties near the second order critical point are discussed.
NASA Astrophysics Data System (ADS)
Kim, Heejae; Murakami, Shuichi
2016-05-01
We construct a theory describing phase transitions between the spinless topological crystalline insulator phase with glide symmetry and a normal insulator phase. We show that a spinless Weyl semimetal phase should intervene between these two phases. Here, because all the bands are free from degeneracy in general, a gap closing between a single conduction band and a single valence band at phase transition generally gives rise to a pair creation of Weyl nodes; hence the Weyl semimetal phase naturally appears. We show the relationship between the change of the Z2 topological number when the system goes through the Weyl semimetal phase, and the trajectory of the Weyl nodes.
NASA Astrophysics Data System (ADS)
Baireuther, P.; Hutasoit, J. A.; Tworzydło, J.; Beenakker, C. W. J.
2016-04-01
We formulate a linear response theory of the chiral magnetic effect in a finite Weyl semimetal, expressing the electrical current density j induced by a slowly oscillating magnetic field B or chiral chemical potential μ in terms of the scattering matrix of Weyl fermions at the Fermi level. Surface conduction can be neglected in the infinite-system limit for δ j/δ μ , but not for δ j/δ B: the chirally circulating surface Fermi arcs give a comparable contribution to the bulk Weyl cones no matter how large the system is, because their smaller number is compensated by an increased flux sensitivity. The Fermi arc contribution to {μ }-1δ j/δ B has the universal value {(e/h)}2, protected by chirality against impurity scattering—unlike the bulk contribution of opposite sign.
Symmetry-protected ideal Weyl semimetal in HgTe-class materials
NASA Astrophysics Data System (ADS)
Ruan, Jiawei; Jian, Shao-Kai; Yao, Hong; Zhang, Haijun; Zhang, Shou-Cheng; Xing, Dingyu
2016-04-01
Ideal Weyl semimetals with all Weyl nodes exactly at the Fermi level and no coexisting trivial Fermi surfaces in the bulk, similar to graphene, could feature deep physics such as exotic transport phenomena induced by the chiral anomaly. Here, we show that HgTe and half-Heusler compounds, under a broad range of in-plane compressive strain, could be materials in nature realizing ideal Weyl semimetals with four pairs of Weyl nodes and topological surface Fermi arcs. Generically, we find that the HgTe-class materials with nontrivial band inversion and noncentrosymmetry provide a promising arena to realize ideal Weyl semimetals. Such ideal Weyl semimetals could further provide a unique platform to study emergent phenomena such as the interplay between ideal Weyl fermions and superconductivity in the half-Heusler compound LaPtBi.
Symmetry-protected ideal Weyl semimetal in HgTe-class materials
NASA Astrophysics Data System (ADS)
Jian, Shao-Kai; Ruan, Jiawei; Yao, Hong; Zhang, Haijun; Zhang, Shou-Cheng; Xing, Dingyu
Ideal Weyl semimetals with all Weyl nodes exactly at the Fermi level and no coexisting trivial Fermi surfaces in the bulk, similar to graphene, could feature deep and novel physics such as exotic transport phenomena induced by the chiral anomaly. Here, we show that HgTe and half-Heusler compounds, under a broad range of inplane compressive strain, could be the first materials in nature realizing ideal Weyl semimetals with four pairs of Weyl nodes and topological surface Fermi arcs. Generically, we find that the HgTe-class materials with nontrivial band inversion and noncentrosymmetry provide a promising arena to realize ideal Weyl semimetals. Such ideal Weyl semimetals could further provide a unique platform to study emergent phenomena such as the interplay between ideal Weyl fermions and superconductivity in the half-Heusler compound LaPtBi.
Symmetry-protected ideal Weyl semimetal in HgTe-class materials.
Ruan, Jiawei; Jian, Shao-Kai; Yao, Hong; Zhang, Haijun; Zhang, Shou-Cheng; Xing, Dingyu
2016-01-01
Ideal Weyl semimetals with all Weyl nodes exactly at the Fermi level and no coexisting trivial Fermi surfaces in the bulk, similar to graphene, could feature deep physics such as exotic transport phenomena induced by the chiral anomaly. Here, we show that HgTe and half-Heusler compounds, under a broad range of in-plane compressive strain, could be materials in nature realizing ideal Weyl semimetals with four pairs of Weyl nodes and topological surface Fermi arcs. Generically, we find that the HgTe-class materials with nontrivial band inversion and noncentrosymmetry provide a promising arena to realize ideal Weyl semimetals. Such ideal Weyl semimetals could further provide a unique platform to study emergent phenomena such as the interplay between ideal Weyl fermions and superconductivity in the half-Heusler compound LaPtBi. PMID:27033588
Symmetry-protected ideal Weyl semimetal in HgTe-class materials
Ruan, Jiawei; Jian, Shao-Kai; Yao, Hong; Zhang, Haijun; Zhang, Shou-Cheng; Xing, Dingyu
2016-01-01
Ideal Weyl semimetals with all Weyl nodes exactly at the Fermi level and no coexisting trivial Fermi surfaces in the bulk, similar to graphene, could feature deep physics such as exotic transport phenomena induced by the chiral anomaly. Here, we show that HgTe and half-Heusler compounds, under a broad range of in-plane compressive strain, could be materials in nature realizing ideal Weyl semimetals with four pairs of Weyl nodes and topological surface Fermi arcs. Generically, we find that the HgTe-class materials with nontrivial band inversion and noncentrosymmetry provide a promising arena to realize ideal Weyl semimetals. Such ideal Weyl semimetals could further provide a unique platform to study emergent phenomena such as the interplay between ideal Weyl fermions and superconductivity in the half-Heusler compound LaPtBi. PMID:27033588
TOPOLOGICAL MATTER. Discovery of a Weyl fermion semimetal and topological Fermi arcs.
Xu, Su-Yang; Belopolski, Ilya; Alidoust, Nasser; Neupane, Madhab; Bian, Guang; Zhang, Chenglong; Sankar, Raman; Chang, Guoqing; Yuan, Zhujun; Lee, Chi-Cheng; Huang, Shin-Ming; Zheng, Hao; Ma, Jie; Sanchez, Daniel S; Wang, BaoKai; Bansil, Arun; Chou, Fangcheng; Shibayev, Pavel P; Lin, Hsin; Jia, Shuang; Hasan, M Zahid
2015-08-01
A Weyl semimetal is a new state of matter that hosts Weyl fermions as emergent quasiparticles and admits a topological classification that protects Fermi arc surface states on the boundary of a bulk sample. This unusual electronic structure has deep analogies with particle physics and leads to unique topological properties. We report the experimental discovery of a Weyl semimetal, tantalum arsenide (TaAs). Using photoemission spectroscopy, we directly observe Fermi arcs on the surface, as well as the Weyl fermion cones and Weyl nodes in the bulk of TaAs single crystals. We find that Fermi arcs terminate on the Weyl fermion nodes, consistent with their topological character. Our work opens the field for the experimental study of Weyl fermions in physics and materials science. PMID:26184916
NASA Technical Reports Server (NTRS)
Bauschlicher, Charles W., Jr.; Langhoff, Stephen R.; Partridge, Harry
1989-01-01
The molecular structure of both the neutral and negatively charged diatomic and triatomic systems containing the Cu, Ag, and Au metals are determined from ab initio calculations. For the neutral triatomic systems, the lowest energy structure is found to be triangular. The relative stability of the 2A1 and 2B2 structures can be predicted simply by knowing the constituent diatomic bond distances and atomic electron affinities (EAs). The lowest energy structure is linear for all of the negative ions. For anionic clusters containing Au, the Au atom(s) preferentially occupy the terminal position(s). The EAs of the heteronuclear systems can be predicted relatively accurately from a weighted average of the corresponding homonuclear systems. Although the theoretical EAs are systematically too small, accurate predictions for the EAs of the triatomics are obtained by uniformly scaling the ab initio results using the accurate experimental EA values available for the atoms and homonuclear diatomics.
Weyl Phases in a Three Dimensional Network Model
NASA Astrophysics Data System (ADS)
Wang, Hailong; Chong, Yidong; theoretical photonics Team
We study the topological properties of 3D ``Floquet'' band structures, defined using unitary evolution matrices rather than Hamiltonians. Such band structures can be realized in coherent-wave networks or lattices subjected to time-periodic drives. Previously, 2D Floquet band structures have been shown to exhibit unusual topological behaviors such as topologically-nontrivial zero-Chern-number phases. Here, we analyze the Floquet band structure of a 3D network model, which exhibits an Floquet analogue of a Weyl phase. The surface states exhibit topologically-protected ``Fermi'' arcs, similar to the recently-discovered Weyl semi-metals; however, the Weyl points in different quasi-energy gaps are related by a particle-hole symmetry which is unique to the Floquet system. By tuning the coupling parameters of the network, we can drive a transition between conventional insulator, weak topological insulator, and Weyl phases. Finally, we discuss the possibility of realizing this model using custom-designed electromagnetic networks. GRANT: Supported by Singapore National Research Foundation under Grant No. NRFF2012-02.
Topological Phonons and Weyl Lines in Three Dimensions
NASA Astrophysics Data System (ADS)
Stenull, Olaf; Kane, C. L.; Lubensky, T. C.
2016-08-01
Topological mechanics and phononics have recently emerged as an exciting field of study. Here we introduce and study generalizations of the three-dimensional pyrochlore lattice that have topologically protected edge states and Weyl lines in their bulk phonon spectra, which lead to zero surface modes that flip from one edge to the opposite as a function of surface wave number.
Topological Phonons and Weyl Lines in Three Dimensions.
Stenull, Olaf; Kane, C L; Lubensky, T C
2016-08-01
Topological mechanics and phononics have recently emerged as an exciting field of study. Here we introduce and study generalizations of the three-dimensional pyrochlore lattice that have topologically protected edge states and Weyl lines in their bulk phonon spectra, which lead to zero surface modes that flip from one edge to the opposite as a function of surface wave number. PMID:27541476
Inflation with a Weyl term, or ghosts at work
Deruelle, Nathalie; Youssef, Ahmed; Sasaki, Misao; Sendouda, Yuuiti E-mail: misao@yukawa.kyoto-u.ac.jp E-mail: ahmed.youssef@apc.univ-paris7.fr
2011-03-01
In order to assess the role of ghosts in cosmology, we study the evolution of linear cosmological perturbations during inflation when a Weyl term is added to the action. Our main results are that vector perturbations can no longer be ignored and that scalar modes diverge in the newtonian gauge but remain bounded in the comoving slicing.
Criteria for Directly Detecting Topological Fermi Arcs in Weyl Semimetals.
Belopolski, Ilya; Xu, Su-Yang; Sanchez, Daniel S; Chang, Guoqing; Guo, Cheng; Neupane, Madhab; Zheng, Hao; Lee, Chi-Cheng; Huang, Shin-Ming; Bian, Guang; Alidoust, Nasser; Chang, Tay-Rong; Wang, BaoKai; Zhang, Xiao; Bansil, Arun; Jeng, Horng-Tay; Lin, Hsin; Jia, Shuang; Hasan, M Zahid
2016-02-12
The recent discovery of the first Weyl semimetal in TaAs provides the first observation of a Weyl fermion in nature and demonstrates a novel type of anomalous surface state, the Fermi arc. Like topological insulators, the bulk topological invariants of a Weyl semimetal are uniquely fixed by the surface states of a bulk sample. Here we present a set of distinct conditions, accessible by angle-resolved photoemission spectroscopy (ARPES), each of which demonstrates topological Fermi arcs in a surface state band structure, with minimal reliance on calculation. We apply these results to TaAs and NbP. For the first time, we rigorously demonstrate a nonzero Chern number in TaAs by counting chiral edge modes on a closed loop. We further show that it is unreasonable to directly observe Fermi arcs in NbP by ARPES within available experimental resolution and spectral linewidth. Our results are general and apply to any new material to demonstrate a Weyl semimetal. PMID:26919005
Morphometric affinities of gigantopithecus.
Gelvin, B R
1980-11-01
Multivariate analyses, supplemented by univariate statistical methods, of measurements from mandibular tooth crown dimensions and the mandible of Gigantopithecus blacki, G. bilaspurensis, Plio-Plelstocene hominids, Homo erectus, and seven Neogene ape species from the genera Proconsul, Sivapithecus, Ouranopithecus, and Dryopithecus were used to assess the morphometric affinities of Gigantopithecus. The results show that Gigantopithecus displays affinities to Ouranopithecus and to the hominids, particularly the Plio-Plelstocene hominids, rather than to the apes. Ouranopithecus demonstrated dental resemblances to G. bilaspurensis and the Plio-Pleistocene hominids but mandibular similarities to the apes. Results of analyses of tooth and mandibular shape indices, combined with multivariate distance and temporal relationships, suggest that Ouranopithecus is a more likely candidate for Gigantopithecus ancestry than is Silvapithecus indicus. Shape and allometric differences between G. bilaspurensis and the robust australopithecines weaken the argument for an ancestral-descendant relationship between these groups. The results support the hypothesis that Gigantopithecus is an extinct side branch of the Hominidae. PMID:7468790
Spectroscopic evidence for a type II Weyl semimetallic state in MoTe2
Huang, Lunan; McCormick, Timothy M.; Ochi, Masayuki; Zhao, Zhiying; Suzuki, Michi -To; Arita, Ryotaro; Wu, Yun; Mou, Daixiang; Cao, Huibo; Yan, Jiaqiang; et al
2016-07-11
In a type I Dirac or Weyl semimetal, the low-energy states are squeezed to a single point in momentum space when the chemical potential μ is tuned precisely to the Dirac/Weyl point1, 2, 3, 4, 5, 6. Recently, a type II Weyl semimetal was predicted to exist, where the Weyl states connect hole and electron bands, separated by an indirect gap7, 8, 9, 10. This leads to unusual energy states, where hole and electron pockets touch at the Weyl point. Here we present the discovery of a type II topological Weyl semimetal state in pure MoTe2, where two sets ofmore » Weyl points (W±2 , W±3) exist at the touching points of electron and hole pockets and are located at different binding energies above EF. Using angle-resolved photoemission spectroscopy, modelling, density functional theory and calculations of Berry curvature, we identify the Weyl points and demonstrate that they are connected by different sets of Fermi arcs for each of the two surface terminations. We also find new surface ‘track states’ that form closed loops and are unique to type II Weyl semimetals. Lastly, this material provides an exciting, new platform to study the properties of Weyl fermions.« less
Experimental discovery of a topological Weyl semimetal state in TaP.
Xu, Su-Yang; Belopolski, Ilya; Sanchez, Daniel S; Zhang, Chenglong; Chang, Guoqing; Guo, Cheng; Bian, Guang; Yuan, Zhujun; Lu, Hong; Chang, Tay-Rong; Shibayev, Pavel P; Prokopovych, Mykhailo L; Alidoust, Nasser; Zheng, Hao; Lee, Chi-Cheng; Huang, Shin-Ming; Sankar, Raman; Chou, Fangcheng; Hsu, Chuang-Han; Jeng, Horng-Tay; Bansil, Arun; Neupert, Titus; Strocov, Vladimir N; Lin, Hsin; Jia, Shuang; Hasan, M Zahid
2015-11-01
Weyl semimetals are expected to open up new horizons in physics and materials science because they provide the first realization of Weyl fermions and exhibit protected Fermi arc surface states. However, they had been found to be extremely rare in nature. Recently, a family of compounds, consisting of tantalum arsenide, tantalum phosphide (TaP), niobium arsenide, and niobium phosphide, was predicted as a Weyl semimetal candidates. We experimentally realize a Weyl semimetal state in TaP. Using photoemission spectroscopy, we directly observe the Weyl fermion cones and nodes in the bulk, and the Fermi arcs on the surface. Moreover, we find that the surface states show an unexpectedly rich structure, including both topological Fermi arcs and several topologically trivial closed contours in the vicinity of the Weyl points, which provides a promising platform to study the interplay between topological and trivial surface states on a Weyl semimetal's surface. We directly demonstrate the bulk-boundary correspondence and establish the topologically nontrivial nature of the Weyl semimetal state in TaP, by resolving the net number of chiral edge modes on a closed path that encloses the Weyl node. This also provides, for the first time, an experimentally practical approach to demonstrating a bulk Weyl fermion from a surface state dispersion measured in photoemission. PMID:26702446
Experimental discovery of a topological Weyl semimetal state in TaP
Xu, Su-Yang; Belopolski, Ilya; Sanchez, Daniel S.; Zhang, Chenglong; Chang, Guoqing; Guo, Cheng; Bian, Guang; Yuan, Zhujun; Lu, Hong; Chang, Tay-Rong; Shibayev, Pavel P.; Prokopovych, Mykhailo L.; Alidoust, Nasser; Zheng, Hao; Lee, Chi-Cheng; Huang, Shin-Ming; Sankar, Raman; Chou, Fangcheng; Hsu, Chuang-Han; Jeng, Horng-Tay; Bansil, Arun; Neupert, Titus; Strocov, Vladimir N.; Lin, Hsin; Jia, Shuang; Hasan, M. Zahid
2015-01-01
Weyl semimetals are expected to open up new horizons in physics and materials science because they provide the first realization of Weyl fermions and exhibit protected Fermi arc surface states. However, they had been found to be extremely rare in nature. Recently, a family of compounds, consisting of tantalum arsenide, tantalum phosphide (TaP), niobium arsenide, and niobium phosphide, was predicted as a Weyl semimetal candidates. We experimentally realize a Weyl semimetal state in TaP. Using photoemission spectroscopy, we directly observe the Weyl fermion cones and nodes in the bulk, and the Fermi arcs on the surface. Moreover, we find that the surface states show an unexpectedly rich structure, including both topological Fermi arcs and several topologically trivial closed contours in the vicinity of the Weyl points, which provides a promising platform to study the interplay between topological and trivial surface states on a Weyl semimetal’s surface. We directly demonstrate the bulk-boundary correspondence and establish the topologically nontrivial nature of the Weyl semimetal state in TaP, by resolving the net number of chiral edge modes on a closed path that encloses the Weyl node. This also provides, for the first time, an experimentally practical approach to demonstrating a bulk Weyl fermion from a surface state dispersion measured in photoemission. PMID:26702446
Affine root systems and dual numbers
NASA Astrophysics Data System (ADS)
Kostyakov, I. V.; Gromov, N. A.; Kuratov, V. V.
The root systems in Carroll spaces with degenerate metric are defined. It is shown that their Cartan matrices and reflection groups are affine. Due to the geometric consideration the root system structure of affine algebras is determined by a sufficiently simple algorithm.
Magnetic Torque Anomaly in the Quantum Limit of Weyl and Dirac Semimetals
NASA Astrophysics Data System (ADS)
Nair, Nityan L.; Moll, Philip J. W.; Potter, Andrew C.; Ramshaw, Brad; Modic, Kimberly; Riggs, Scott; Zeng, Bin; Ghimire, Nirmal; Bauer, Eric; Kealhofer, Robert; Li, Zhenglu; Louie, Steven; Ronning, Filip; Analytis, James G.
Three dimensional Dirac and Weyl semimetals, characterized by bulk quasiparticles that behave as massless, linearly dispersing Dirac or Weyl fermions, have excited physicists with their unique topological properties and potential for applications. The experimental signatures of Weyl or Dirac fermions, however, are often subtle and indirect, especially in systems where they coexist with trivial electrons. Here, we report a novel method by which these topological systems can be unambiguously experimentally identified. Magnetic torque measurements were performed on the Weyl semimetal NbAs in high magnetic field, showing a large anomaly upon entering the quantum limit. The torque exhibits a striking sign reversal, corresponding to a change in the magnetic anisotropy that is a direct result of the topological properties of the charge carriers. This result can be generalized to other Dirac and Weyl semimetal systems and establishes quantum limit torque measurements as a simple and direct experimental method of distinguishing topologically non-trivial Weyl and Dirac systems from trivial semiconductors.
Weyl points in three-dimensional optical lattices: synthetic magnetic monopoles in momentum space
NASA Astrophysics Data System (ADS)
Buljan, Hrvoje; Dubcek, Tena; Kennedy, Colin; Lu, Ling; Ketterle, Wolfgang; Soljacic, Marin
2015-05-01
We show that Hamiltonians with Weyl points can be realized for ultracold atoms using laser-assisted tunneling in three-dimensional (3D) optical lattices. Weyl points are synthetic magnetic monopoles that exhibit a robust, 3D linear dispersion (e.g., see). They are associated with many interesting topological states of matter, such as Weyl semimetals and chiral Weyl fermions. However, Weyl points have yet to be experimentally observed in any system. We show that this elusive goal is well-within experimental reach with an extension of the techniques recently used to obtain the Harper Hamiltonian. We propose using laser assisted tunneling to create a 3D optical lattice, with specifically designed hopping between lattice sites that breaks inversion symmetry. The design leads to creation of four Weyl points in the Brillouin zone of the lattice, which are verified to be monopoles of the synthetic magnetic field. Supported by the Unity through Knowledge Fund (Grant 5/13).
Reproducing pairs and the continuous nonstationary Gabor transform on LCA groups
NASA Astrophysics Data System (ADS)
Speckbacher, Michael; Balazs, Peter
2015-10-01
In this paper we introduce and investigate the concept of reproducing pairs as a generalization of continuous frames. Reproducing pairs yield a bounded analysis and synthesis process while the frame condition can be omitted at both stages. Moreover, we will investigate certain continuous frames (resp. reproducing pairs) on LCA groups, which can be described as a continuous version of nonstationary Gabor systems and state sufficient conditions for these systems to form a continuous frame (resp. reproducing pair). As a byproduct we identify the structure of the frame operator (resp. resolution operator). We will apply our results to systems generated by a unitary action of a subset of the affine Weyl-Heisenberg group in {L}2({{R}}). This setup will also serve as a nontrivial example of a system for which, whereas continuous frames exist, no dual system with the same structure exists even if we drop the frame property.
NASA Astrophysics Data System (ADS)
Kim, Kyoung-Min; Shin, Dongwoo; Sasaki, M.; Kim, Heon-Jung; Kim, Jeehoon; Kim, Ki-Seok
2016-08-01
It is at the heart of modern condensed matter physics to investigate the role of a topological structure in anomalous transport phenomena. In particular, chiral anomaly turns out to be the underlying mechanism for the negative longitudinal magnetoresistivity in a Weyl metal phase. The existence of a dissipationless current channel causes enhancement of electric currents along the direction of a pair of Weyl points or applied magnetic fields (B ). However, temperature (T ) dependence of the negative longitudinal magnetoresistivity has not been understood yet in the presence of disorder scattering since it is not clear at all how to introduce effects of disorder scattering into the topological-in-origin transport coefficient at finite temperatures. The calculation based on the Kubo formula of the current-current correlation function is simply not known for this anomalous transport coefficient. Combining the renormalization group analysis with the Boltzmann transport theory to encode the chiral anomaly, we reveal how disorder scattering renormalizes the distance between a pair of Weyl points and such a renormalization effect modifies the topological-in-origin transport coefficient at finite temperatures. As a result, we find breakdown of B /T scaling, given by B /T1 +η with 0 <η <1 . This breakdown may be regarded to be a fingerprint of the interplay between disorder scattering and topological structure in a Weyl metal phase.
Bhattacharya, Sarbani; Liang, Zhong; Quek, Adam J.; Ploplis, Victoria A.; Law, Ruby; Castellino, Francis J.
2014-01-01
A emm53 subclass of Group A Streptococcus pyogenes (GAS) interacts tightly with human plasma plasminogen (hPg) and plasmin (hPm) via the kringle 2 (K2hPg) domain of hPg/hPm and the N-terminal a1a2 regions of a GAS coiled-coil M-like protein (PAM). Previous studies have shown that a monomeric PAM fragment, VEK30 (residues 97–125 + Tyr), interacted specifically with isolated K2hPg. However, the binding strength of VEK30 (KD = 56 nm) was ∼60-fold weaker than that of full-length dimeric PAM (KD = 1 nm). To assess whether this attenuated binding was due to the inability of VEK30 to dimerize, we defined the minimal length of PAM required to dimerize using a series of peptides with additional PAM residues placed at the NH2 and COOH termini of VEK30. VEK64 (PAM residues 83–145 + Tyr) was found to be the smallest peptide that adopted an α-helical dimer, and was bound to K2hPg with nearly the same affinity as PAM (KD = 1–2 nm). However, addition of two PAM residues (Arg126-His127) to the COOH terminus of VEK30 (VEK32) maintained a monomeric peptidic structure, but exhibited similar K2hPg binding affinity as full-length dimeric PAM. We identified five residues in a1a2 (Arg113, His114, Glu116, Arg126, His127), mutation of which reduced PAM binding affinity for K2hPg by ∼1000-fold. Replacement of these critical residues by Ala in the GAS genome resulted in reduced virulence, similar to the effects of inactivating the PAM gene entirely. We conclude that rather than dimerization of PAM, the five key residues in the binding domain of PAM are essential to mediate the high affinity interaction with hPg, leading to increased GAS virulence. PMID:24962580
Bhattacharya, Sarbani; Liang, Zhong; Quek, Adam J; Ploplis, Victoria A; Law, Ruby; Castellino, Francis J
2014-08-01
A emm53 subclass of Group A Streptococcus pyogenes (GAS) interacts tightly with human plasma plasminogen (hPg) and plasmin (hPm) via the kringle 2 (K2hPg) domain of hPg/hPm and the N-terminal a1a2 regions of a GAS coiled-coil M-like protein (PAM). Previous studies have shown that a monomeric PAM fragment, VEK30 (residues 97-125 + Tyr), interacted specifically with isolated K2hPg. However, the binding strength of VEK30 (KD = 56 nm) was ∼60-fold weaker than that of full-length dimeric PAM (KD = 1 nm). To assess whether this attenuated binding was due to the inability of VEK30 to dimerize, we defined the minimal length of PAM required to dimerize using a series of peptides with additional PAM residues placed at the NH2 and COOH termini of VEK30. VEK64 (PAM residues 83-145 + Tyr) was found to be the smallest peptide that adopted an α-helical dimer, and was bound to K2hPg with nearly the same affinity as PAM (KD = 1-2 nm). However, addition of two PAM residues (Arg(126)-His(127)) to the COOH terminus of VEK30 (VEK32) maintained a monomeric peptidic structure, but exhibited similar K2hPg binding affinity as full-length dimeric PAM. We identified five residues in a1a2 (Arg(113), His(114), Glu(116), Arg(126), His(127)), mutation of which reduced PAM binding affinity for K2hPg by ∼ 1000-fold. Replacement of these critical residues by Ala in the GAS genome resulted in reduced virulence, similar to the effects of inactivating the PAM gene entirely. We conclude that rather than dimerization of PAM, the five key residues in the binding domain of PAM are essential to mediate the high affinity interaction with hPg, leading to increased GAS virulence. PMID:24962580
Analog simulation of Weyl particles with cold atoms
NASA Astrophysics Data System (ADS)
Rabinovic, Mihail; Suchet, Daniel; Reimann, Thomas; Kretzschmar, Norman; Sievers, Franz; Salomon, Christophe; Lau, Jonathan; Lobo, Carlos; Goulko, Olga; Chevy, Frederic
2016-05-01
The high degree of control of the properties of ultracold gases offers the possibility to study experimentally unconventional many-body systems. An example is given by massless relativistic Weyl fermions, which are of particular interest in high energy and condensed matter physics, where they emerge in the form of low energy excitations of exotic compounds like TaAs. The particular case of harmonically trapped Weyl particles can be mimicked by a laser-cooled cloud of 6Li trapped in a magnetic quadrupole potential. The non-separability of this particular potential enables a quasi-thermalization of the single particle distribution function even in the absence of interactions. Surprisingly, the dynamics features an effective decoupling between the strong trapping axis and the weak trapping plane. We studied both, numerically and experimentally, the relaxation of the excited cloud towards its equilibrium distribution, mapping this dynamics directly to the case of non-interaction massless particles in a harmonic potential.
Wormhole geometries in fourth-order conformal Weyl gravity
NASA Astrophysics Data System (ADS)
Varieschi, Gabriele U.; Ault, Kellie L.
2016-04-01
We present an analysis of the classic wormhole geometries based on conformal Weyl gravity, rather than standard general relativity. The main characteristics of the resulting traversable wormholes remains the same as in the seminal study by Morris and Thorne, namely, that effective super-luminal motion is a viable consequence of the metric. Improving on previous work on the subject, we show that for particular choices of the shape and redshift functions the wormhole metric in the context of conformal gravity does not violate the main energy conditions at or near the wormhole throat. Some exotic matter might still be needed at the junction between our solutions and flat spacetime, but we demonstrate that the averaged null energy condition (as evaluated along radial null geodesics) is satisfied for a particular set of wormhole geometries. Therefore, if fourth-order conformal Weyl gravity is a correct extension of general relativity, traversable wormholes might become a realistic solution for interstellar travel.
The Weyl-Cartan Gauss-Bonnet gravity
NASA Astrophysics Data System (ADS)
Haghani, Zahra; Khosravi, Nima; Shahidi, Shahab
2015-11-01
In this paper, we consider the generalized Gauss-Bonnet action in four-dimensional Weyl-Cartan spacetime. In this spacetime, the presence of a torsion tensor and Weyl vector implies that the generalized Gauss-Bonnet action will not be a total derivative in four-dimensional spacetime. It will be shown that the higher than two time derivatives can be removed from the action by choosing a suitable set of parameters. In the special case where only the trace part of the torsion remains, the model reduces to general relativity plus two vector fields, one of which is massless and the other is massive. We will then obtain the healthy region of the five-dimensional parameter space of the theory in some special cases.
The semiclassical coherent state propagator in the Weyl representation
Braun, Carol; Li, Feifei; Garg, Anupam; Stone, Michael
2015-12-15
It is shown that the semiclassical coherent state propagator takes its simplest form when the quantum mechanical Hamiltonian is replaced by its Weyl symbol in defining the classical action, in that there is then no need for a Solari-Kochetov correction. It is also shown that such a correction exists if a symbol other than the Weyl symbol is chosen and that its form is different depending on the symbol chosen. The various forms of the propagator based on different symbols are shown to be equivalent provided the correspondingly correct Solari-Kochetov correction is included. All these results are shown for both particle and spin coherent state propagators. The global anomaly in the fluctuation determinant is further elucidated by a study of the connection between the discrete fluctuation determinant and the discrete Jacobi equation.
On the null trajectories in conformal Weyl gravity
Villanueva, J.R.; Olivares, Marco E-mail: marco.olivaresrubilar@gmail.com
2013-06-01
In this work we find analytical solutions to the null geodesics around a black hole in the conformal Weyl gravity. Exact expressions for the horizons are found, and they depend on the cosmological constant and the coupling constants of the conformal Weyl gravity. Then, we study the radial motion from the point of view of the proper and coordinate frames, and compare it with that found in spacetimes of general relativity. The angular motion is also examined qualitatively by means of an effective potential; quantitatively, the equation of motion is solved in terms of wp-Weierstrass elliptic function. Thus, we find the deflection angle for photons without using any approximation, which is a novel result for this kind of gravity.
Electronic properties in a quantum well structure of Weyl semimetal
NASA Astrophysics Data System (ADS)
You, Wen-Long; Wang, Xue-Feng; Oleś, Andrzej M.; Zhou, Jiao-Jiao
2016-04-01
We investigate the confined states and transport of three-dimensional Weyl electrons around a one-dimensional external rectangular electrostatic potential. The confined states with finite transverse wave vector exist at energies higher than the half well depth or lower than the half barrier height. The rectangular potential appears completely transparent to the normal incident electrons but not otherwise. The tunneling transmission coefficient is sensitive to their incident angle and shows resonant peaks when their energy coincides with the confined spectra. In addition, for the electrons in the conduction (valence) band through a potential barrier (well), the transmission spectrum has a gap of width increasing with the incident angle. Interestingly, the electron linear zero-temperature conductance over the potential can approach zero when the Fermi energy is aligned to the top and bottom energies of the potential, when only electron beams normal to the potential interfaces can pass through. The considered structure can be used to collimate the Weyl electron beams.
Wormhole geometries in fourth-order conformal Weyl gravity
NASA Astrophysics Data System (ADS)
Varieschi, Gabriele; Ault, Kellie
2016-03-01
We present an analysis of the classic wormhole geometries based on conformal Weyl gravity, rather than standard general relativity. The main characteristics of the resulting traversable wormholes remain the same as in the seminal study by Morris and Thorne, namely, that effective super-luminal motion is a viable consequence of the metric. Improving on previous work on the subject, we show that for particular choices of the shape and redshift functions, the wormhole metric in the context of conformal gravity does not violate the main energy conditions, as was the case of the original solutions. In particular, the resulting geometry does not require the use of exotic matter at or near the wormhole throat. Therefore, if fourth-order conformal Weyl gravity is a correct extension of general relativity, traversable wormholes might become a realistic solution for interstellar travel. This work was supported by a Grant from the Frank R. Seaver College of Science and Engineering, Loyola Marymount University.
Weirdest Martensite: Smectic Liquid Crystal Microstructure and Weyl-Poincaré Invariance
NASA Astrophysics Data System (ADS)
Liarte, Danilo B.; Bierbaum, Matthew; Mosna, Ricardo A.; Kamien, Randall D.; Sethna, James P.
2016-04-01
Smectic liquid crystals are remarkable, beautiful examples of materials microstructure, with ordered patterns of geometrically perfect ellipses and hyperbolas. The solution of the complex problem of filling three-dimensional space with domains of focal conics under constraining boundary conditions yields a set of strict rules, which are similar to the compatibility conditions in a martensitic crystal. Here we present the rules giving compatible conditions for the concentric circle domains found at two-dimensional smectic interfaces with planar boundary conditions. Using configurations generated by numerical simulations, we develop a clustering algorithm to decompose the planar boundaries into domains. The interfaces between different domains agree well with the smectic compatibility conditions. We also discuss generalizations of our approach to describe the full three-dimensional smectic domains, where the variant symmetry group is the Weyl-Poincaré group of Lorentz boosts, translations, rotations, and dilatations.
Weirdest Martensite: Smectic Liquid Crystal Microstructure and Weyl-Poincaré Invariance.
Liarte, Danilo B; Bierbaum, Matthew; Mosna, Ricardo A; Kamien, Randall D; Sethna, James P
2016-04-01
Smectic liquid crystals are remarkable, beautiful examples of materials microstructure, with ordered patterns of geometrically perfect ellipses and hyperbolas. The solution of the complex problem of filling three-dimensional space with domains of focal conics under constraining boundary conditions yields a set of strict rules, which are similar to the compatibility conditions in a martensitic crystal. Here we present the rules giving compatible conditions for the concentric circle domains found at two-dimensional smectic interfaces with planar boundary conditions. Using configurations generated by numerical simulations, we develop a clustering algorithm to decompose the planar boundaries into domains. The interfaces between different domains agree well with the smectic compatibility conditions. We also discuss generalizations of our approach to describe the full three-dimensional smectic domains, where the variant symmetry group is the Weyl-Poincaré group of Lorentz boosts, translations, rotations, and dilatations. PMID:27104728
Analog simulation of Weyl particles with cold atoms
NASA Astrophysics Data System (ADS)
Suchet, Daniel; Rabinovic, Mihail; Reimann, Thomas; Kretschmar, Norman; Sievers, Franz; Salomon, Christophe; Lau, Johnathan; Goulko, Olga; Lobo, Carlos; Chevy, Frédéric
2016-04-01
In this letter we report on a novel approach to study the dynamics of harmonically confined Weyl particles using magnetically trapped fermionic atoms. We find that after a kick of its center of mass, the system relaxes towards a steady state even in the absence of interactions, in stark contrast with massive particles which would oscillate without damping. Remarkably, the equilibrium distribution is non-Boltzmann, exhibiting a strong anisotropy which we study both numerically and experimentally.
Chiral anomaly and classical negative magnetoresistance of Weyl metals
NASA Astrophysics Data System (ADS)
Son, D. T.; Spivak, B. Z.
2013-09-01
We consider the classical magnetoresistance of a Weyl metal in which the electron Fermi surface possesses nonzero fluxes of the Berry curvature. Such a system may exhibit large negative magnetoresistance with unusual anisotropy as a function of the angle between the electric and magnetic fields. In this case the system can support an additional type of plasma wave. These phenomena are consequences of the chiral anomaly in electron transport theory.
On Weyl wormholes supported by massless K-essence
Estevez-Delgado, J.; Zannias, T.
2008-12-04
We show that Weyl wormholes supported by mass-less K-essence can be generated by a pair of axisymmetric harmonic functions. We study properties of space-times generated by harmonic functions describing the exterior potential of a thin conducting disk held at fixed potential. We find that within this family, only a particular subfamily generates wormholes and the resulting wormholes are necessarily spherical. In general, the topology of the space-times generated by an arbitrary pair is multi sheeted.
Magnetotransport phenomena related to the chiral anomaly in Weyl semimetals
NASA Astrophysics Data System (ADS)
Spivak, B. Z.; Andreev, A. V.
2016-02-01
We present a theory of magnetotransport phenomena related to the chiral anomaly in Weyl semimetals. We show that conductivity, thermal conductivity, thermoelectric, and the sound absorption coefficients exhibit strong and anisotropic magnetic field dependencies. We also discuss properties of magnetoplasmons and magnetopolaritons, whose existences are entirely determined by the chiral anomaly. Finally, we discuss the conditions of applicability of the quasiclassical description of electron transport phenomena related to the chiral anomaly.
Intrinsic diamagnetism in the Weyl semimetal TaAs
NASA Astrophysics Data System (ADS)
Liu, Yu; Li, Zhilin; Guo, Liwei; Chen, Xiaolong; Yuan, Ye; Liu, Fang; Prucnal, Slawomir; Helm, Manfred; Zhou, Shengqiang
2016-06-01
We investigate the magnetic properties of TaAs, a prototype Weyl semimetal. TaAs crystals show diamagnetism with magnetic susceptibility of about -7×10-7 emu/(g Oe) at 5 K. A general feature is the appearance of a minimum at around 185 K in magnetization measurements as a function of temperature, which resembles that of graphite. No phase transition is observed in the temperature range between 5 K and 400 K.
Possible superconductivity in Weyl semimetal NbP
NASA Astrophysics Data System (ADS)
Kumar, P.; Sudesh, Patnaik, S.
2016-05-01
In the present paper, we have observed the possible superconductivity in polycrystalline NbP compound. This belongs to the so called Weyl Semimetal family where there is band crossing and linear dispersion point near the Fermi level. Critical temperature calculated from the resistivity measurement is found near 7.5 K. Superconductivity is also confirmed from the magnetization measurement. In the normal state, this sample shows significant magneto-resistance.
Gauge equivalence in QCD: The Weyl and Coulomb gauges
NASA Astrophysics Data System (ADS)
Haller, Kurt; Ren, Hai-Cang
2003-10-01
The Weyl-gauge (Aa0=0) QCD Hamiltonian is unitarily transformed to a representation in which it is expressed entirely in terms of gauge-invariant quark and gluon fields. In a subspace of gauge-invariant states we have constructed that implement the non-Abelian Gauss’s law, this unitarily transformed Weyl-gauge Hamiltonian can be further transformed and, under appropriate circumstances, can be identified with the QCD Hamiltonian in the Coulomb gauge. We demonstrate an isomorphism that materially facilitates the application of this Hamiltonian to a variety of physical processes, including the evaluation of S-matrix elements. This isomorphism relates the gauge-invariant representation of the Hamiltonian and the required set of gauge-invariant states to a Hamiltonian of the same functional form but dependent on ordinary unconstrained Weyl-gauge fields operating within a space of “standard” perturbative states. The fact that the gauge-invariant chromoelectric field is not Hermitian has important implications for the functional form of the Hamiltonian finally obtained. When this non-Hermiticity is taken into account, the “extra” vertices in the Christ-Lee’ Coulomb-gauge Hamiltonian are natural outgrowths of the formalism. When this non-Hermiticity is neglected, the Hamiltonian used in the earlier work of Gribov and others results.
A Note on Holographic Superconductors with Weyl Corrections
NASA Astrophysics Data System (ADS)
Momeni, D.; Setare, M. R.
We study analytical properties of the holographic superconductors with Weyl corrections. We describe the phenomena in the probe limit neglecting backreaction of the spacetime. We observe that for the conformal dimension \\xutri;+ = 3, the minimum value of the critical temperature T Min c at which condensation sets, can be obtained directly from the equations of motion as T Min c≈ 0.170845\\root3 \\of {ρ }, which is in very good agreement with the numerical value T Min c = 0.170\\root3 \\of {ρ } [Phys. Lett. B 697, 153 (2011)]. This value of T Min c corresponds to the value of the Weyl's coupling γ = -0.06 in Table 1 of Phys. Lett. B 697, 153 (2011). We calculate the T Min c ≈ 0.21408\\root3 \\of {ρ } for another Weyl's coupling γ = 0.02 and the conformal dimension \\xutri- = 1. Further, we show that the critical exponent is β = (1)/(2). We observe that there is a linear relation between the charge density ρ and the chemical potential difference μ-μc qualitatively matches the numerical curves.
Implications of Einstein-Weyl Causality on Quantum Mechanics
NASA Astrophysics Data System (ADS)
Bendaniel, David
A fundamental physical principle that has consequences for the topology of space-time is the principle of Einstein-Weyl causality. This also has quantum mechanical manifestations. Borchers and Sen have rigorously investigated the mathematical implications of Einstein-Weyl causality and shown the denumerable space-time Q2 would be implied. They were left with important philosophical paradoxes regarding the nature of the physical real line E, e.g., whether E = R, the real line of mathematics. In order to remove these paradoxes an investigation into a constructible foundation is suggested. We have pursued such a program and find it indeed provides a dense, denumerable space-time and, moreover, an interesting connection with quantum mechanics. We first show that this constructible theory contains polynomial functions which are locally homeomorphic with a dense, denumerable metric space R* and are inherently quantized. Eigenfunctions governing fields can then be effectively obtained by computational iteration. Postulating a Lagrangian for fields in a compactified space-time, we get a general description of which the Schrodinger equation is a special case. From these results we can then also show that this denumerable space-time is relational (in the sense that space is not infinitesimally small if and only if it contains a quantized field) and, since Q2 is imbedded in R*2, it directly fulfills the strict topological requirements for Einstein-Weyl causality. Therefore, the theory predicts that E = R*.
Universal optical conductivity of a disordered Weyl semimetal
Roy, Bitan; Juričić, Vladimir; Das Sarma, Sankar
2016-01-01
Topological Weyl semimetals, besides manifesting chiral anomaly, can also accommodate a disorder-driven unconventional quantum phase transition into a metallic phase. A fundamentally and practically important question in this regard concerns an experimentally measurable quantity that can clearly distinguish these two phases. We show that the optical conductivity while serving this purpose can also play the role of a bonafide order parameter across such disorder-driven semimetal-metal quantum phase transition by virtue of displaying distinct scaling behavior in the semimetallic and metallic phases, as well as inside the quantum critical fan supporting a non-Fermi liquid. We demonstrate that the correction to the dielectric constant and optical conductivity in a dirty Weyl semimetal due to weak disorder is independent of the actual nature of point-like impurity scatterers. Therefore, optical conductivity can be used as an experimentally measurable quantity to study the critical properties and to pin the universality class of the disorder-driven quantum phase transition in Weyl semimetals. PMID:27573668
Universal optical conductivity of a disordered Weyl semimetal.
Roy, Bitan; Juričić, Vladimir; Das Sarma, Sankar
2016-01-01
Topological Weyl semimetals, besides manifesting chiral anomaly, can also accommodate a disorder-driven unconventional quantum phase transition into a metallic phase. A fundamentally and practically important question in this regard concerns an experimentally measurable quantity that can clearly distinguish these two phases. We show that the optical conductivity while serving this purpose can also play the role of a bonafide order parameter across such disorder-driven semimetal-metal quantum phase transition by virtue of displaying distinct scaling behavior in the semimetallic and metallic phases, as well as inside the quantum critical fan supporting a non-Fermi liquid. We demonstrate that the correction to the dielectric constant and optical conductivity in a dirty Weyl semimetal due to weak disorder is independent of the actual nature of point-like impurity scatterers. Therefore, optical conductivity can be used as an experimentally measurable quantity to study the critical properties and to pin the universality class of the disorder-driven quantum phase transition in Weyl semimetals. PMID:27573668
Origin of dissipative Fermi arc transport in Weyl semimetals
NASA Astrophysics Data System (ADS)
Gorbar, E. V.; Miransky, V. A.; Shovkovy, I. A.; Sukhachov, P. O.
2016-06-01
By making use of a low-energy effective model of Weyl semimetals, we show that the Fermi arc transport is dissipative. The origin of the dissipation is the scattering of the surface Fermi arc states into the bulk of the semimetal. It is noticeable that the corresponding scattering rate is nonzero and can be estimated even in a perturbative theory, although in general the reliable calculations of transport properties necessitate a nonperturbative approach. Nondecoupling of the surface and bulk sectors in the low-energy theory of Weyl semimetals invalidates the usual argument of a nondissipative transport due to one-dimensional arc states. This property of Weyl semimetals is in drastic contrast to that of topological insulators, where the decoupling is protected by a gap in the bulk. Within the framework of the linear response theory, we obtain an approximate result for the conductivity due to the Fermi arc states and analyze its dependence on chemical potential, temperature, and other parameters of the model.
Nanostructured Carbon Allotropes with Weyl-like Loops and Points.
Chen, Yuanping; Xie, Yuee; Yang, Shengyuan A; Pan, Hui; Zhang, Fan; Cohen, Marvin L; Zhang, Shengbai
2015-10-14
Carbon allotropes are subject of intense investigations for their superb structural, electronic, and chemical properties, but not for topological band properties because of the lack of strong spin-orbit coupling (SOC). Here, we show that conjugated p-orbital interactions, common to most carbon allotropes, can in principle produce a new type of topological band structure, forming the so-called Weyl-like semimetal in the absence of SOC. Taking a structurally stable interpenetrated graphene network (IGN) as example, we show, by first-principles calculations and tight-binding modeling, that its Fermi surface is made of two symmetry-protected Weyl-like loops with linear dispersion along perpendicular directions. These loops are reduced to Weyl-like points upon breaking of the inversion symmetry. Because of the topological properties of these band-structure anomalies, remarkably, at a surface terminated by vacuum there emerges a flat band in the loop case and two Fermi arcs in the point case. These topological carbon materials may also find applications in the fields of catalysts. PMID:26426355