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topological phases

Ariel Haimovici, Pablo Balenzuela, Enzo Tagliazucchi
Synchronization of brain activity fluctuations is believed to represent communication between spatially distant neural processes. These inter-areal functional interactions develop in the background of a complex network of axonal connections linking cortical and sub-cortical neurons, termed the human "structural connectome". Theoretical considerations and experimental evidence support the view that the human brain can be modeled as a system operating at a critical point between ordered (sub-critical) and disordered (super-critical) phases...
October 19, 2016: Brain Connectivity
Tristan da Câmara Santa Clara Gomes, Joaquín De La Torre Medina, Matthieu Lemaitre, Luc Piraux
Track-etched polymer membranes with crossed nanochannels have been revealed to be most suitable as templates to produce large surface area and mechanically stable 3D interconnected nanowire (NW) networks by electrodeposition. Geometrically controlled NW superstructures made of NiCo ferromagnetic alloys exhibit appealing magnetoresistive properties. The combination of exact alloy compositions with the spatial arrangement of NWs in the 3D network is decisive to obtain specific magnetic and magneto-transport behavior...
December 2016: Nanoscale Research Letters
Chi-Ho Cheung, Huei-Ru Fuh, Ming-Chien Hsu, Yeu-Chung Lin, Ching-Ray Chang
Recently, searching large-bulk band gap topological insulator (TI) is under intensive study. Through k·P theory and first-principles calculations analysis on antimonene, we find that α-phase antimonene can be tuned to a 2D TI under an in-plane anisotropic strain and the magnitude of direct bulk band gap (SOC gap) depends on the strength of spin-orbit coupling (SOC) which is strain-dependent. As the band inversion of this TI accompanies with an indirect band gap, the TI bulk band gap is the indirect band gap, not the SOC gap...
December 2016: Nanoscale Research Letters
Tilen Čadež, Pedro D Sacramento
We study Majorana zero energy modes (MZEM) that occur in an s-wave superconducting surface, at the ends of a ferromagnetic (FM) chain of adatoms, in the presence of Rashba spin-orbit interaction (SOI) considering both non self-consistent and self-consistent superconducting order. We find that in the self-consistent solution, the average superconducting gap function over the adatom sites has a discontinuous drop with increasing exchange interaction at the same critical value where the topological phase transition occurs...
October 18, 2016: Journal of Physics. Condensed Matter: An Institute of Physics Journal
Yung-Han Shih, Kuen-Yun Wang, Brenda T Singco, Chia-Her Lin, Hsi-Ya Huang
In this study, we first demonstrated the effect of two types of metal-organic framework-polymer (MOF-polymer) monoliths on in-tube solid-phase microextraction (IT-SPME) of sulfonamides. Sulfonamides were successfully adsorbed onto MIL-101(Cr)-polymer but were difficult to elute due to these sulfonamides could interact via Lewis acid-base interaction with the presence of Cr(III) coordinatively unsaturated metal sites (CUS). Moreover, the cage-type topology of MIL-101(Cr) that could produce multiple pathways thus complicates the desorption of the test analytes from the sorbent...
October 17, 2016: Langmuir: the ACS Journal of Surfaces and Colloids
Yonghui Zhou, Pengchao Lu, Yongping Du, Xiangde Zhu, Ganghua Zhang, Ranran Zhang, Dexi Shao, Xuliang Chen, Xuefei Wang, Mingliang Tian, Jian Sun, Xiangang Wan, Zhaorong Yang, Wenge Yang, Yuheng Zhang, Dingyu Xing
We report a new pressure-induced phase in TaAs with different Weyl fermions than the ambient structure with the aid of theoretical calculations, experimental transport and synchrotron structure investigations up to 53 GPa. We show that TaAs transforms from an ambient I4_{1}md phase (t-TaAs) to a high-pressure hexagonal P-6m2  (h-TaAs) phase at 14 GPa, along with changes of the electronic state from containing 24 Weyl nodes distributed at two energy levels to possessing 12 Weyl nodes at an isoenergy level, which substantially reduces the interference between the surface and bulk states...
September 30, 2016: Physical Review Letters
David Bouttes, Emmanuelle Gouillart, Damien Vandembroucq
The crucial role of hydrodynamic pinch-off instabilities is evidenced in the coarsening stage of viscous liquids. The phase separation of a barium borosilicate glass melt is studied by in situ synchrotron tomography at high temperature. The high viscosity contrast between the less viscous phase and the more viscous phase induces a topological symmetry breaking: capillary breakups occur preferentially in the less viscous phase. As a result, contrasting morphologies are obtained in the two phases. This symmetry breaking is illustrated on three different glass compositions, corresponding to different volume fractions of the two phases...
September 30, 2016: Physical Review Letters
Daniel Leykam, Y D Chong
We show theoretically that a photonic topological insulator can support edge solitons that are strongly self-localized and propagate unidirectionally along the lattice edge. The photonic topological insulator consists of a Floquet lattice of coupled helical waveguides, in a medium with local Kerr nonlinearity. The soliton behavior is strongly affected by the topological phase of the linear lattice. The topologically nontrivial phase gives a continuous family of solitons, while the topologically trivial phase gives an embedded soliton that occurs at a single power and arises from a self-induced local nonlinear shift in the intersite coupling...
September 30, 2016: Physical Review Letters
James E McClure, Mark A Berrill, William G Gray, Cass T Miller
Multiphase flows in porous medium systems are typically modeled at the macroscale by applying the principles of continuum mechanics to develop models that describe the behavior of averaged quantities, such as fluid pressure and saturation. These models require closure relations to produce solvable forms. One of these required closure relations is an expression relating the capillary pressure to fluid saturation and, in some cases, other topological invariants such as interfacial area and the Euler characteristic (or average Gaussian curvature)...
September 2016: Physical Review. E
Ji Ho Ryu, Han Sol Wee, Won Bo Lee
Various microstructures are obtained through the self-assembly of block copolymers on the basis of the compositional fractions and repulsive interactions among different types of beads. The inhomogeneity of block copolymers can be studied by molecular dynamics. However, preparing initial configurations of various self-assembled structures directly by molecular dynamics requires extensive computational time because of topological constraints. Furthermore, manual preparation often becomes a complicated and time-consuming procedure even for the simplest structures, such as a lamellar phase, not to mention three-dimensional bicontinuous cubic phases such as a gyroid phase...
September 2016: Physical Review. E
Marco A Amaral, Lucas Wardil, Matjaž Perc, Jafferson K L da Silva
In times of plenty expectations rise, just as in times of crisis they fall. This can be mathematically described as a win-stay-lose-shift strategy with dynamic aspiration levels, where individuals aspire to be as wealthy as their average neighbor. Here we investigate this model in the realm of evolutionary social dilemmas on the square lattice and scale-free networks. By using the master equation and Monte Carlo simulations, we find that cooperators coexist with defectors in the whole phase diagram, even at high temptations to defect...
September 2016: Physical Review. E
A V Sorokin, M Aparicio Alcalde, V M Bastidas, G Engelhardt, D G Angelakis, T Brandes
In this work we study a one-dimensional lattice of Lipkin-Meshkov-Glick models with alternating couplings between nearest-neighbors sites, which resembles the Su-Schrieffer-Heeger model. Typical properties of the underlying models are present in our semiclassical-topological hybrid system, allowing us to investigate an interplay between semiclassical bifurcations at mean-field level and topological phases. Our results show that bifurcations of the energy landscape lead to diverse ordered quantum phases. Furthermore, the study of the quantum fluctuations around the mean-field solution reveals the existence of nontrivial topological phases...
September 2016: Physical Review. E
Chris Jozwiak, Jonathan A Sobota, Kenneth Gotlieb, Alexander F Kemper, Costel R Rotundu, Robert J Birgeneau, Zahid Hussain, Dung-Hai Lee, Zhi-Xun Shen, Alessandra Lanzara
Topological insulators host spin-polarized surface states born out of the energetic inversion of bulk bands driven by the spin-orbit interaction. Here we discover previously unidentified consequences of band-inversion on the surface electronic structure of the topological insulator Bi2Se3. By performing simultaneous spin, time, and angle-resolved photoemission spectroscopy, we map the spin-polarized unoccupied electronic structure and identify a surface resonance which is distinct from the topological surface state, yet shares a similar spin-orbital texture with opposite orientation...
October 14, 2016: Nature Communications
Calvin Zhang, Timothy J Lewis
Many neuronal circuits driving coordinated locomotion are composed of chains of half-center oscillators (HCOs) of various lengths. The HCO is a common motif in central pattern generating circuits (CPGs); an HCO consists of two neurons, or two neuronal populations, connected by reciprocal inhibition. To maintain appropriate motor coordination for effective locomotion over a broad range of frequencies, chains of CPGs must produce approximately constant phase-differences in a robust manner. In this article, we study phase-locking in chains of nearest-neighbor coupled HCOs and examine how the circuit architecture can promote phase-constancy, i...
October 13, 2016: Journal of Mathematical Biology
Michael Niklas, Mónica Benito, Sigmund Kohler, Gloria Platero
We analyze an AC-driven dimer chain connected to a strongly biased electron source and drain. It turns out that the resulting transport exhibits fingerprints of topology. They are particularly visible in the driving-induced current suppression and the Fano factor. Thus, shot noise measurements provide a topological phase diagram as a function of the driving parameters. The observed phenomena can be explained physically by a mapping to an effective time-independent Hamiltonian and the emergence of edge states...
November 11, 2016: Nanotechnology
Yue Wu, Sebastian Henke, Gregor Kieslich, Inke Schwedler, Miaosen Yang, Duncan A X Fraser, Dermot O'Hare
Versatility in metal substitution is one of the key aspects of metal-organic framework (MOF) chemistry, allowing properties to be tuned in a rational way. As a result, it important to understand why MOF syntheses involving different metals arrive at or fail to produce the same topological outcome. Frequently, conditions are tuned by trial-and-error to make MOFs with different metal species. We ask: is it possible to adjust synthetic conditions in a systematic way in order to design routes to desired phases? We have used in situ X-ray powder diffraction to study the solvothermal formation of isostructural M2 (bdc)2 dabco (M=Zn, Co, Ni) pillared-paddlewheel MOFs in real time...
October 11, 2016: Angewandte Chemie
Sobhit Singh, Wilfredo Ibarra-Hernández, Irais Valencia-Jaime, Guillermo Avendaño-Franco, Aldo H Romero
Semi-conducting alloys BixSb1-x have emerged as a potential candidate for topological insulators and are well known for their novel thermoelectric properties. In this work, we present a systematic study of the low-energy phases of 35 different compositions of BixSb1-x (0 < x < 1) at zero temperature and zero pressure. We explore the potential energy surface of BixSb1-x as a function of Sb concentration by using the ab initio minima hopping structural search method. Even though Bi and Sb crystallize in the same R3[combining macron]m space group, our calculations indicate that BixSb1-x alloys can have several other thermodynamically stable crystal structures...
September 30, 2016: Physical Chemistry Chemical Physics: PCCP
Ye Zhou, Ashley Guo, Rui Zhang, Julio C Armas-Perez, José A Martínez-González, Mohammad Rahimi, Monirosadat Sadati, Juan J de Pablo
There is considerable interest in understanding and controlling topological defects in nematic liquid crystals (LCs). Confinement, in the form of droplets, has been particularly effective in that regard. Here, we employ a Landau-de Gennes formalism to explore the geometrical frustration of nematic order in shell geometries, and focus on chiral materials. By varying the chirality and thickness in uniform shells, we construct a phase diagram that includes tetravalent structures, bipolar structures (BS), bent structures and radial spherical structures (RSS)...
September 30, 2016: Soft Matter
David F Mross, Jason Alicea, Olexei I Motrunich
We introduce a particle-hole-symmetric metallic state of bosons in a magnetic field at odd-integer filling. This state hosts composite fermions whose energy dispersion features a quadratic band touching and corresponding 2π Berry flux protected by particle-hole and discrete rotation symmetries. We also construct an alternative particle-hole symmetric state-distinct in the presence of inversion symmetry-without Berry flux. As in the Dirac composite Fermi liquid introduced by Son [Phys. Rev. X 5, 031027 (2015)], breaking particle-hole symmetry recovers the familiar Chern-Simons theory...
September 23, 2016: Physical Review Letters
Lijuan Shi, Panpan Sun, Liqiang Zheng
Gemini supra-amphiphiles with different spacer lengths, [M-n-M](2+)@2[DBS](-) (n = 2, 6, 10), were easily constructed. The conformational flexibility and hydrophobicity of the spacer group can be effectively tailored through regulating the spacer length, leading to the fine control of the topologies and subsequent hierarchical self-assemblies of [M-n-M](2+)@2[DBS](-). Vesicles are primarily fabricated by [M-n-M](2+)@2[DBS](-), and then successively fused into vesicle clusters, nanotubes, and planar bilayers, whose bilayer curvatures are gradually decreased, with increasing spacer length...
October 7, 2016: Soft Matter
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