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topological phases

Bartomeu Monserrat, David Vanderbilt
We study the effects of temperature on the band structure of the Bi_{2}Se_{3} family of topological insulators using first-principles methods. Increasing temperature drives these materials towards the normal state, with similar contributions from thermal expansion and from electron-phonon coupling. The band gap changes with temperature reach 0.3 eV at 600 K, of similar size to the changes caused by electron correlation. Our results suggest that temperature-induced topological phase transitions should be observable near critical points of other external parameters...
November 25, 2016: Physical Review Letters
Peng Zou, Joachim Brand, Xia-Ji Liu, Hui Hu
We investigate traveling solitons of a one- or two-dimensional spin-orbit-coupled Fermi superfluid in both topologically trivial and nontrivial regimes by solving the static and time-dependent Bogoliubov-de Gennes equations. We find a critical velocity v_{h} for traveling solitons that is much smaller than the value predicted using the Landau criterion due to spin-orbit coupling. Above v_{h}, our time-dependent simulations in harmonic traps indicate that traveling solitons decay by radiating sound waves. In the topological phase, we predict the existence of peculiar Majorana solitons, which host two Majorana fermions and feature a phase jump of π across the soliton, irrespective of the velocity of travel...
November 25, 2016: Physical Review Letters
Zhaoju Yang, Baile Zhang
Lorentz-violating type-II Weyl fermions, which were missed in Weyl's prediction of nowadays classified type-I Weyl fermions in quantum field theory, have recently been proposed in condensed matter systems. The semimetals hosting type-II Weyl fermions offer a rare platform for realizing many exotic physical phenomena that are different from type-I Weyl systems. Here we construct the acoustic version of a type-II Weyl Hamiltonian by stacking one-dimensional dimerized chains of acoustic resonators. This acoustic type-II Weyl system exhibits distinct features in a finite density of states and unique transport properties of Fermi-arc-like surface states...
November 25, 2016: Physical Review Letters
Se Kwon Kim, Héctor Ochoa, Ricardo Zarzuela, Yaroslav Tserkovnyak
We study a spin Hamiltonian for spin-orbit-coupled ferromagnets on the honeycomb lattice. At sufficiently low temperatures supporting the ordered phase, the effective Hamiltonian for magnons, the quanta of spin-wave excitations, is shown to be equivalent to the Haldane model for electrons, which indicates the nontrivial topology of the band and the existence of the associated edge state. At high temperatures comparable to the ferromagnetic-exchange strength, we take the Schwinger-boson representation of spins, in which the mean-field spinon band forms a bosonic counterpart of the Kane-Mele model...
November 25, 2016: Physical Review Letters
Matteo Fraschini, Matteo Demuru, Arjan Hillebrand, Lorenza Cuccu, Silvia Porcu, Francesca Di Stefano, Monica Puligheddu, Gianluca Floris, Giuseppe Borghero, Francesco Marrosu
Amyotrophic Lateral Sclerosis (ALS) is one of the most severe neurodegenerative diseases, which is known to affect upper and lower motor neurons. In contrast to the classical tenet that ALS represents the outcome of extensive and progressive impairment of a fixed set of motor connections, recent neuroimaging findings suggest that the disease spreads along vast non-motor connections. Here, we hypothesised that functional network topology is perturbed in ALS, and that this reorganization is associated with disability...
December 7, 2016: Scientific Reports
Karen Caeyenberghs, Helena Verhelst, Adam Clemente, Peter H Wilson
OBJECTIVE: Traumatic brain injury (TBI) is associated with cognitive and motor deficits, and poses a significant personal, societal, and economic burden. One mechanism by which TBI is thought to affect cognition and behaviour is through changes in functional connectivity. Graph theory is a powerful framework for quantifying topological features of neuroimaging-derived functional networks. The objective of this paper is to review studies examining functional connectivity in TBI with an emphasis on graph theoretical analysis that is proving to be valuable in uncovering network abnormalities in this condition...
December 2, 2016: NeuroImage
Giacomo Russo, Lucia Grumetto, Francesco Barbato, Giulio Vistoli, Alessandro Pedretti
The present study proposes a method for an in silico calculation of phospholipophilicity. Phospholipophilicity is intended as the measure of analyte affinity for phospholipids; it is currently assessed by HPLC measures of analyte retention on phosphatidylcholine-like stationary phases (IAM - Immobilized Artificial Membrane) resulting in log kW(IAM) values. Due to the amphipathic and electrically charged nature of phospholipids, retention on these stationary phases results from complex mechanisms, being affected not only by lipophilicity (as measured by n-octanol/aqueous phase partition coefficients, log P) but also by the occurrence of polar and/or electrostatic intermolecular interaction forces...
December 2, 2016: European Journal of Pharmaceutical Sciences
Ilya Belopolski, Daniel S Sanchez, Yukiaki Ishida, Xingchen Pan, Peng Yu, Su-Yang Xu, Guoqing Chang, Tay-Rong Chang, Hao Zheng, Nasser Alidoust, Guang Bian, Madhab Neupane, Shin-Ming Huang, Chi-Cheng Lee, You Song, Haijun Bu, Guanghou Wang, Shisheng Li, Goki Eda, Horng-Tay Jeng, Takeshi Kondo, Hsin Lin, Zheng Liu, Fengqi Song, Shik Shin, M Zahid Hasan
The recent discovery of a Weyl semimetal in TaAs offers the first Weyl fermion observed in nature and dramatically broadens the classification of topological phases. However, in TaAs it has proven challenging to study the rich transport phenomena arising from emergent Weyl fermions. The series MoxW1-xTe2 are inversion-breaking, layered, tunable semimetals already under study as a promising platform for new electronics and recently proposed to host Type II, or strongly Lorentz-violating, Weyl fermions. Here we report the discovery of a Weyl semimetal in MoxW1-xTe2 at x=25%...
December 5, 2016: Nature Communications
Briana Vecchio-Pagán, Scott M Blackman, Melissa Lee, Melis Atalar, Matthew J Pellicore, Rhonda G Pace, Arianna L Franca, Karen S Raraigh, Neeraj Sharma, Michael R Knowles, Garry R Cutting
Extensive phenotypic variability is commonly observed in individuals with Mendelian disorders, even among those with identical genotypes in the disease-causing gene. To determine whether variants within and surrounding CFTR contribute to phenotypic variability in cystic fibrosis (CF), we performed deep sequencing of CFTR in 762 patients homozygous for the common CF-causing variant, F508del. In phase 1, ~200 kb encompassing CFTR and extending 10 kb 5' and 5 kb 3' of the gene was sequenced in 486 F508del homozygotes selected from the extremes of sweat chloride concentration...
2016: Human Genome Variation
E V Panov, W Baumjohann, R A Wolf, R Nakamura, V Angelopoulos, J M Weygand, M V Kubyshkina
Violent releases of space plasma energy from the Earth's magnetotail during substorms produce strong electric currents and bright aurora. But what modulates these currents and aurora and controls dissipation of the energy released in the ionosphere? Using data from the THEMIS fleet of satellites and ground-based imagers and magnetometers, we show that plasma energy dissipation is controlled by field-aligned currents (FACs) produced and modulated during magnetotail topology change and oscillatory braking of fast plasma jets at 10-14 Earth radii in the nightside magnetosphere...
December 2016: Nature Physics
Malek Boukallaba, Boutheïna Kerkeni, Christine Lepetit, Dorothée Berthomieu
A quantum chemistry study of mononuclear metal coordination with four 4-methylimidazole ligands (4-MeIm) was investigated. The four complexes [Cu(4-MeIm)4](2+), [Cu(4-MeIm)4, H2O](2+), [Zn(4-MeIm)4](2+) and [Zn(4-MeIm)4, H2O](2+) were studied with particular attention to the Nπ or Nτ possible coordinations of the 4-MeIm ring with the metals, using different DFT methods. The results suggest that the Nτ coordination of 4-MeIm ring to Zn(II) or Cu(II) is more favorable whatever the level of calculation. In contrast, the addition of one water molecule in the first coordination sphere of the metal ions provides five-coordinated complexes showing no Nπ or Nτ preferences...
December 2016: Journal of Molecular Modeling
Michael Schuler, Seth Whitsitt, Louis-Paul Henry, Subir Sachdev, Andreas M Läuchli
The low-energy spectra of many body systems on a torus, of finite size L, are well understood in magnetically ordered and gapped topological phases. However, the spectra at quantum critical points separating such phases are largely unexplored for (2+1)D systems. Using a combination of analytical and numerical techniques, we accurately calculate and analyze the low-energy torus spectrum at an Ising critical point which provides a universal fingerprint of the underlying quantum field theory, with the energy levels given by universal numbers times 1/L...
November 18, 2016: Physical Review Letters
Per Sebastian Skardal, Dane Taylor, Jie Sun, Alex Arenas
We study the dynamics of network-coupled phase oscillators in the presence of coupling frustration. It was recently demonstrated that in heterogeneous network topologies, the presence of coupling frustration causes perfect phase synchronization to become unattainable even in the limit of infinite coupling strength. Here, we consider the important case of heterogeneous coupling functions and extend previous results by deriving analytical predictions for the total erosion of synchronization. Our analytical results are given in terms of basic quantities related to the network structure and coupling frustration...
June 1, 2016: Physica D. Nonlinear Phenomena
Jolanta Kwasniewska, Arita Kus, Monika Swoboda, Agnieszka Braszewska-Zalewska
The temporal and spatial properties of DNA replication in plants related to DNA damage and mutagenesis is poorly understood. Experiments were carried out to explore the relationships between DNA replication, chromatin structure and DNA damage in nuclei from barley root tips. We quantitavely analysed the topological organisation of replication foci using pulse EdU labelling during the S phase and its relationship with the DNA damage induced by mutagenic treatment with maleic hydrazide (MH), nitroso-N-methyl-urea (MNU) and gamma ray...
December 2016: Mutation Research
Xiangyang Guan, Cynthia Chen, Dan Work
Networks can evolve even on a short-term basis. This phenomenon is well understood by network scientists, but receive little attention in empirical literature involving real-world networks. On one hand, this is due to the deceitfully fixed topology of some networks such as many physical infrastructures, whose evolution is often deemed unlikely to occur in short term; on the other hand, the lack of data prohibits scientists from studying subjects such as social networks that seem likely to evolve on a short-term basis...
2016: PloS One
Rui-Pin Chen, Khian-Hooi Chew, Guoquan Zhou, Chao-Qing Dai, Sailing He
The collapse dynamics of a structured optical field with a distribution of spatially-variant states of polarization (SoP) and a spiral phase in the field cross section is studied using the two-dimensional coupled nonlinear Schrӧdinger equations. The self-focusing of a structured optical field with an inhomogeneous SoP distribution can give rise to new phenomena of collapse dynamics that is completely different from a scalar field. The collapse patterns are closely related to the topological charges of the vortexas well as the polarization, the initial power, and the SoP distribution in the field cross section...
November 28, 2016: Optics Express
Sushanta Kumar Pal, P Senthilkumaran
The sign rule requires that adjacent singularities on a contour have opposite signs and hence cultivation of lemon only fields poses problem as all lemons have positive index. In this paper we show that the interference of three linearly polarized plane waves can create regions of ellipse and vector fields in 2-dimensions (2D) in which a lemon lattice is interlaced in a V-point lattice. The lemons appear at intensity maxima of the lattice structure while the V-points take care of index conservation by sitting at intensity minima...
November 28, 2016: Optics Express
Freek Ruesink, Mohammad-Ali Miri, Andrea Alù, Ewold Verhagen
Nonreciprocal components, such as isolators and circulators, provide highly desirable functionalities for optical circuitry. This motivates the active investigation of mechanisms that break reciprocity, and pose alternatives to magneto-optic effects in on-chip systems. In this work, we use optomechanical interactions to strongly break reciprocity in a compact system. We derive minimal requirements to create nonreciprocity in a wide class of systems that couple two optical modes to a mechanical mode, highlighting the importance of optically biasing the modes at a controlled phase difference...
November 29, 2016: Nature Communications
Tetsuyuki Ochiai
We study the effects of a synthetic gauge field and pseudospin-orbit interaction in a stacked two-dimensional ring-network model. The model was introduced to simulate light propagation in the corresponding ring-resonator lattice, and is thus completely bosonic. Without these two items, the model exhibits Floquet-Weyl and Floquet-topological-insulator phases with topologically gapless and gapped band structures, respectively. The synthetic magnetic field implemented in the model results in a three-dimensional Hofstadter-butterfly-type spectrum in a photonic platform...
February 1, 2017: Journal of Physics. Condensed Matter: An Institute of Physics Journal
Dafei Jin, Ling Lu, Zhong Wang, Chen Fang, John D Joannopoulos, Marin Soljačić, Liang Fu, Nicholas X Fang
Classical wave fields are real-valued, ensuring the wave states at opposite frequencies and momenta to be inherently identical. Such a particle-hole symmetry can open up new possibilities for topological phenomena in classical systems. Here we show that the historically studied two-dimensional (2D) magnetoplasmon, which bears gapped bulk states and gapless one-way edge states near-zero frequency, is topologically analogous to the 2D topological p+ip superconductor with chiral Majorana edge states and zero modes...
November 28, 2016: Nature Communications
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