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topological phases

Qi Wei, Jia-Jia Wang, Jie Zhang, Guo-Yu Yang
Two three-dimensional (3D) zeolitic open-framework aluminoborates (ABOs) [Zn(ma)(en)2][AlB5O10] (1) and [Zn(ma)(en)2][AlB6O11(OH)] (2) (ma = methylamine, en = ethylenediamine) were successfully made under solvothermal conditions, which represent the first examples using similar metal complex (MC) with mixed amines as the structure-directing agents in ABOs. Notice that the central atom in the MC is coordinated by mixed amines is uncommon. However, they exhibit distinctly different structures: 1 crystallizes in a centrosymmetric [Al(B5O10)]n(2n-) zeolitic framework built by pentaborate (B5O10) clusters and AlO4 tetrahedra, exhibiting a 4-connected cag topology, while 2 contains hexaborate (B6O11(OH)) clusters and AlO4 groups, further alternately joined to form a noncentrosymmetric [AlB6O11(OH)]n(2n-) zeolitic framework with 7-/9-, 8-/10-ring helical channels and large 13-ring channels, showing a dia topology...
May 19, 2017: Inorganic Chemistry
Gong Chen, Sang Pyo Kang, Colin Ophus, Alpha T N'Diaye, Hee Young Kwon, Ryan T Qiu, Changyeon Won, Kai Liu, Yizheng Wu, Andreas K Schmid
Chiral spin textures in ultrathin films, such as skyrmions or chiral domain walls, are believed to offer large performance advantages in the development of novel spintronics technologies. While in-plane magnetized films have been studied extensively as media for current- and field-driven domain wall dynamics with applications in memory or logic devices, the stabilization of chiral spin textures in in-plane magnetized films has remained rare. Here we report a phase of spin structures in an in-plane magnetized ultrathin film system where out-of-plane spin orientations within domain walls are stable...
May 19, 2017: Nature Communications
Ce Wang, Pengfei Zhang, Xin Chen, Jinlong Yu, Hui Zhai
We show how the topological number of a static Hamiltonian can be measured from a dynamical quench process. We focus on a two-band Chern insulator in two dimension, for instance, the Haldane model, whose dynamical process can be described by a mapping from the [k_{x},k_{y},t] space to the Bloch sphere, characterized by the Hopf invariant. Such a mapping has been constructed experimentally by measurements in cold atom systems. We show that, taking any two constant vectors on the Bloch sphere, their inverse images of this mapping are two trajectories in the [k_{x},k_{y},t] space, and the linking number of these two trajectories exactly equals the Chern number of the static Hamiltonian...
May 5, 2017: Physical Review Letters
Steve M Young, Benjamin J Wieder
Filling-enforced Dirac semimetals, or those required at specific fillings by the combination of crystalline and time-reversal symmetries, have been proposed in numerous materials. However, Dirac points in these materials are not generally robust against breaking or modifying time-reversal symmetry. We present a new class of two-dimensional Dirac semimetal protected by the combination of crystal symmetries and a special, antiferromagnetic time-reversal symmetry. Systems in this class of magnetic layer groups, while having broken time-reversal symmetry, still respect the operation of time-reversal followed by a half-lattice translation...
May 5, 2017: Physical Review Letters
Pierpaolo Sorrentino, Dagmar Nieboer, Jos Twisk, Cornelis J Stam, Linda Douw, Arjan Hillebrand
Recently, a large study demonstrated that lower serum levels of insulin growth factor-1 (IGF-1) relate to brain atrophy and to greater risk for developing Alzheimer's disease in a healthy elderly population. We set out to test if functional brain networks relate to IGF-1 levels in the middle-aged. Hence, we studied the association between IGF-1 and magnetoencephalography-based functional network characteristics in a middle-aged population. The functional connections between brain areas were estimated for six frequency bands (delta, theta, alpha1, alpha2, beta, gamma) using the phase lag index (PLI)...
May 18, 2017: Brain Connectivity
Zamirbek Akimbekov, Athanassios D Katsenis, G P Nagabhushana, Ghada Ayoub, Mihails Arhangelskis, Andrew J Morris, Tomislav Friscic, Alexandra Navrotsky
We provide the first combined experimental and theoretical evaluation of how differences in ligand structure and framework to-pology affect the relative stabilities of isocompositional (i.e. true polymorph) metal-organic frameworks (MOFs). We used solution calorimetry and periodic DFT calculations to analyze thermodynamics of two families of topologically-distinct polymorphs of zinc zeolitic imidazolate frameworks (ZIFs) based on 2-methyl- and 2-ethylimidazolate linkers, demonstrating a correlation between measured thermodynamic stability and density, and a pronounced effect of the ligand substituent on their stability...
May 18, 2017: Journal of the American Chemical Society
Thomas Schweigler, Valentin Kasper, Sebastian Erne, Igor Mazets, Bernhard Rauer, Federica Cataldini, Tim Langen, Thomas Gasenzer, Jürgen Berges, Jörg Schmiedmayer
Quantum systems can be characterized by their correlations. Higher-order (larger than second order) correlations, and the ways in which they can be decomposed into correlations of lower order, provide important information about the system, its structure, its interactions and its complexity. The measurement of such correlation functions is therefore an essential tool for reading, verifying and characterizing quantum simulations. Although higher-order correlation functions are frequently used in theoretical calculations, so far mainly correlations up to second order have been studied experimentally...
May 17, 2017: Nature
Zengji Yue, Gaolei Xue, Juan Liu, Yongtian Wang, Min Gu
Holography has extremely extensive applications in conventional optical instruments spanning optical microscopy and imaging, three-dimensional displays and metrology. To integrate holography with modern low-dimensional electronic devices, holograms need to be thinned to a nanometric scale. However, to keep a pronounced phase shift modulation, the thickness of holograms has been generally limited to the optical wavelength scale, which hinders their integration with ultrathin electronic devices. Here, we break this limit and achieve 60 nm holograms using a topological insulator material...
May 18, 2017: Nature Communications
M D Thomson, K Rabia, F Meng, M Bykov, S van Smaalen, H G Roskos
Charge density waves (CDWs), i.e. the periodic spatial modulation of coupled electronic and lattice density, are ubiquitous in low-dimensional conductors and have taken on renewed relevance due their role in state-of-the-art materials, e.g. high-T c superconductors, topological insulators and low-dimensional carbon. As CDWs are described by a complex order parameter to represent both the amplitude and phase, they are formally analogous to BCS superconductors and spin-waves, providing a prototype of collective phenomena for the further development of field theories and ab-initio calculations of complex solids...
May 17, 2017: Scientific Reports
Shuichi Murakami, Motoaki Hirayama, Ryo Okugawa, Takashi Miyake
A band gap for electronic states in crystals governs various properties of solids, such as transport, optical, and magnetic properties. Its estimation and control have been an important issue in solid-state physics. The band gap can be controlled externally by various parameters, such as pressure, atomic compositions, and external field. Sometimes, the gap even collapses by tuning some parameter. In the field of topological insulators, this closing of the gap at a time-reversal invariant momentum indicates a band inversion, that is, it leads to a topological phase transition from a normal insulator to a topological insulator...
May 2017: Science Advances
Shiu-Ming Huang, You-Jhih Yan, Shih-Hsun Yu, Mitch Chou
The conductivity increases as thickness decreases in a series of Sb2SeTe2 topological insulator nanosheets with thickness ranging from 80 to 200 nm, where the sheet conductance is proportional to the thickness. The corresponding sheet conductance of the surface state is 8.7 e(2)/h which is consistent with the values extracted from the temperature dependent Shubnikov-de Haas oscillations at high magnetic fields. The extracted Fermi momentum is the same as the results from the ARPES value, and the Berry phase is π...
May 15, 2017: Scientific Reports
Sujit Sarkar
An attempt is made to understand the topological quantum phase transition, emergence of relativistic modes and local topological order of light in a strongly interacting light-matter system. We study this system, in a one dimensional array of nonlinear cavities. Topological quantum phase transition occurs with massless excitation only for the finite detuning process. We present a few results based on the exact analytical calculations along with the physical explanations. We observe the emergence of massive Majorana fermion mode at the topological state, massless Majorana-Weyl fermion mode during the topological quantum phase transition and Dirac fermion mode for the non-topological state...
May 12, 2017: Scientific Reports
Fernando Iemini, Christophe Mora, Leonardo Mazza
Parafermions are emergent excitations that generalize Majorana fermions and can also realize topological order. In this Letter, we present a nontrivial and quasi-exactly-solvable model for a chain of parafermions in a topological phase. We compute and characterize the ground-state wave functions, which are matrix-product states and have a particularly elegant interpretation in terms of Fock parafermions, reflecting the factorized nature of the ground states. Using these wave functions, we demonstrate analytically several signatures of topological order...
April 28, 2017: Physical Review Letters
Yao Yu, Ran Shang, Sa Chen, Bing-Wu Wang, Zheming Wang, Song Gao
A series of AlNa bimetallic ammonium metal formate frameworks (AlNa AMFFs) have been prepared by employing various ammoniums from the smallest NH4+ to larger linear polyammoniums. The series consists of six perovskites of (412*63) topology for mono-ammoniums, two chiral (49*66) frameworks incorporating polyethylene-ammoniums, two niccolites with (412*63)(49*66) topology containing diammoniums, and two layered compounds made of 2D (4,4) AlNa-formate sheets intercalated by small diammoniums. The first ten compounds present the structural hierarchy of (412*63)m(49*66)n framework topologies for (m, n) = (1, 0), (0, 1), and (1, 1), respectively, in parallel to the homometallic AMFFs for divalent metals...
May 12, 2017: Chemistry: a European Journal
D R Gulevich, D Yudin, D V Skryabin, I V Iorsh, I A Shelykh
Matter in nontrivial topological phase possesses unique properties, such as support of unidirectional edge modes on its interface. It is the existence of such modes which is responsible for the wonderful properties of a topological insulator - material which is insulating in the bulk but conducting on its surface, along with many of its recently proposed photonic and polaritonic analogues. We show that exciton-polariton fluid in a nontrivial topological phase in kagome lattice, supports nonlinear excitations in the form of solitons built up from wavepackets of topological edge modes - topological edge solitons...
May 11, 2017: Scientific Reports
Brigitta Tóth, Gábor Urbán, Gábor P Háden, Molnár Márk, Miklós Török, Cornelis Jan Stam, István Winkler
The organization of functional brain networks changes across human lifespan. The present study analyzed functional brain networks in healthy full-term infants (N = 139) within 1-6 days from birth by measuring neural synchrony in EEG recordings during quiet sleep. Large-scale phase synchronization was measured in six frequency bands with the Phase Lag Index. Macroscopic network organization characteristics were quantified by constructing unweighted minimum spanning tree graphs. The cortical networks in early infancy were found to be significantly more hierarchical and had a more cost-efficient organization compared with MST of random control networks, more so in the theta and alpha than in other frequency bands...
May 10, 2017: Human Brain Mapping
Huimin Chen, Lin Li, Qinqing Zhu, Jinhu Yang, Bin Chen, Qianhui Mao, Jianhua Du, Hangdong Wang, Minghu Fang
The so-called Dirac materials such as graphene and topological insulators are a new class of matter different from conventional metals and (doped) semiconductors. Superconductivity induced by doing or applying pressure in these systems may be unconventional, or host mysterious Majorana fermions. Here, we report a successfully observation of pressure-induced superconductivity in an antiferromagnetic Dirac material BaMnBi2 with T c of ~4 K at 2.6 GPa. Both the higher upper critical field, μ 0 H c2(0) ~ 7 Tesla, and the measured current independent of T c precludes that superconductivity is ascribed to the Bi impurity...
May 9, 2017: Scientific Reports
Harsha Agarwal, Matthias Reisser, Celina Wortmann, J Christof M Gebhardt
The three-dimensional arrangement of chromatin encodes regulatory traits important for nuclear processes such as transcription and replication. Chromatin topology is in part mediated by the architectural protein CCCTC-binding factor (CTCF) that binds to the boundaries of topologically associating domains. Whereas sites of CTCF interactions are well characterized, little is known on how long CTCF binds to chromatin and how binding evolves during the cell cycle. We monitored CTCF-chromatin interactions by live cell single molecule tracking in different phases of the cell cycle...
May 6, 2017: Biophysical Journal
Abhishek Banerjee, Oindrila Deb, Kunjalata Majhi, R Ganesan, Diptiman Sen, P S Anil Kumar
We demonstrate experimentally that a macroscopic topological insulator (TI) phase can emerge in a granular conductor composed of an assembly of tunnel coupled TI nanocrystals of dimension ∼10 nm × 10 nm × 2 nm. Electrical transport measurements on thin films of Bi2Se3 nanocrystals reveal the presence of decoupled top and bottom topological surface states that exhibit large surface state penetration depths (∼30 nm at 2 K). By tuning the size of the nanocrystals and the couplings between them, this new class of TIs may be readily tuned from a non-topological to a topological insulator phase, that too with designer properties...
May 9, 2017: Nanoscale
Manousos A Klados, Niki Pandria, Sifis Micheloyannis, Daniel Margulies, Panagiotis D Bamidis
Following our previous work regarding the involvement of math anxiety (MA) in math-oriented tasks, this study tries to explore the differences in the cerebral networks' topology between self-reported low math-anxious (LMA) and high math-anxious (HMA) individuals, during the anticipation phase prior to a mathematical related experiment. For this reason, multichannel EEG recordings were adopted, while the solution of the inverse problem was applied in a generic head model, in order to obtain the cortical signals...
May 5, 2017: International Journal of Psychophysiology
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