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topological phases

Michael Hell, Martin Leijnse, Karsten Flensberg
We model theoretically a two-dimensional electron gas (2DEG) covered by a superconductor and demonstrate that topological superconducting channels are formed when stripes of the superconducting layer are removed. As a consequence, Majorana bound states (MBSs) are created at the ends of the stripes. We calculate the topological invariant and energy gap of a single stripe, using realistic values for an InAs 2DEG proximitized by an epitaxial Al layer. We show that the topological gap is enhanced when the structure is made asymmetric...
March 10, 2017: Physical Review Letters
N Xu, G Autès, C E Matt, B Q Lv, M Y Yao, F Bisti, V N Strocov, D Gawryluk, E Pomjakushina, K Conder, N C Plumb, M Radovic, T Qian, O V Yazyev, J Mesot, H Ding, M Shi
The Weyl semimetal phase is a recently discovered topological quantum state of matter characterized by the presence of topologically protected degeneracies near the Fermi level. These degeneracies are the source of exotic phenomena, including the realization of chiral Weyl fermions as quasiparticles in the bulk and the formation of Fermi arc states on the surfaces. Here, we demonstrate that these two key signatures show distinct evolutions with the bulk band topology by performing angle-resolved photoemission spectroscopy, supported by first-principles calculations, on transition-metal monophosphides...
March 10, 2017: Physical Review Letters
Biao-Qi Chen, Ranjith Kumar Kankala, Ai-Zheng Chen, Ding-Zhu Yang, Xiao-Xia Cheng, Ni-Na Jiang, Kai Zhu, Shi-Bin Wang
Attempts to reflect the physiology of organs is quite an intricacy during the tissue engineering process. An ideal scaffold and its surface topography can address and manipulate the cell behavior during the regeneration of targeted tissue, affecting the cell growth and differentiation significantly. Herein, silk fibroin (SF) nanoparticles were incorporated into poly(l-lactic acid) (PLLA) to prepare composite scaffolds via phase-inversion technique using supercritical carbon dioxide (SC-CO2). The SF nanoparticle core increased the surface roughness and hydrophilicity of the PLLA scaffolds, leading to a high affinity for albumin attachment...
2017: International Journal of Nanomedicine
Pengfei Lv, Yu Liu, Zhe Wang, Shuyang Liu, Lanlan Jiang, Junlin Chen, Yongchen Song
The wettability of porous media is of major interest in a broad range of natural and engineering applications. The wettability of a fluid on a solid surface is usually evaluated by the contact angle between them. While in situ local contact angle measurements are complicated by the topology of porous media, which can make it difficult to use traditional methods, recent advances in microfocused X-ray computed tomography (micro-CT) and image processing techniques have made it possible to measure contact angles on the scale of the pore sizes in such media...
March 22, 2017: Langmuir: the ACS Journal of Surfaces and Colloids
S P Lepkowski, Witold Bardyszewski
We study theoretically the topological phase transition and the Rashba spin-orbit interaction in electrically biased InN/GaN quantum wells. We show that that for properly chosen widths of quantum wells and barriers, one can effectively tune the system through the topological phase transition applying an external electric field perpendicular to the QW plane. We find that in InN/GaN quantum wells with the inverted band structure, when the conduction band s-type level is below the heavy hole and light hole p-type levels, the spin splitting of the subbands decreases with increasing the amplitude of the electric field in the quantum wells, which reveals the anomalous Rashba effect...
March 22, 2017: Journal of Physics. Condensed Matter: An Institute of Physics Journal
Stephanie R Taylor, Thomas J Wang, Daniel Granados-Fuentes, Erik D Herzog
Although the suprachiasmatic nucleus (SCN) has long been considered the master circadian clock in mammals, the topology of the connections that synchronize daily rhythms among SCN cells is not well understood. We combined experimental and computational methods to infer the directed interactions that mediate circadian synchrony between regions of the SCN. We analyzed PERIOD2 (PER2) expression from SCN slices during and after treatment with tetrodotoxin, allowing us to map connections as cells resynchronized their daily cycling following blockade and restoration of cell-cell communication...
February 2017: Journal of Biological Rhythms
A G Hansen, N Ramakrishnan, P B Sunil Kumar, J H Ipsen
The properties of self-avoiding p-atic membranes restricted to spherical topology have been studied by Monte Carlo simulations of a triangulated random surface model. Spherically shaped p-atic membranes undergo a Kosterlitz-Thouless transition as expected with topology induced mutually repelling disclinations of the p-atic ordered phase. For flexible membranes the phase behaviour bears some resemblance to the spherically shaped case with a p-atic disordered crumpled phase and p-atic ordered, conformationally ordered (crinkled) phase separated by a KT-like transition with proliferation of disclinations...
March 2017: European Physical Journal. E, Soft Matter
Michael J Frazier, Dennis M Kochmann
A mechanical metamaterial, a simple, periodic mechanical structure, is reported, which reproduces the nonlinear dynamic behavior of materials undergoing phase transitions and domain switching at the structural level. Tunable multistability is exploited to produce switching and transition phenomena whose kinetics are governed by the same Allen-Cahn law commonly used to describe material-level, structural-transition processes. The reported purely elastic mechanical system displays several key features commonly found in atomic- or mesoscale physics of solids...
March 21, 2017: Advanced Materials
Fitsum Mesadi, Mujdat Cetin, Tolga Tasdizen
Level set methods are widely used for image segmentation because of their convenient shape representation for numerical computations, and capability to handle topological changes. However, in spite of the numerous works in the literature, the use of level set methods in image segmentation still has several drawbacks. These shortcomings include formation of irregularities of the signed distance function, sensitivity to initialization, lack of locality, and expensive computational cost which increases dramatically as the number of objects to be simultaneously segmented grows...
March 15, 2017: IEEE Transactions on Image Processing: a Publication of the IEEE Signal Processing Society
M Martínez-Negro, G Caracciolo, S Palchetti, D Pozzi, A L Capriotti, C Cavaliere, A Laganà, C Ortiz Mellet, J M Benito, J M García Fernández, E Aicart, E Junquera
The self-assembling processes underlining the capabilities of facially differentiated ("Janus") polycationic amphiphilic cyclodextrins (paCDs) as non-viral gene nanocarriers have been investigated by a pluridisciplinary approach. Three representative Janus paCDs bearing a common tetradecahexanoyl multitail domain at the secondary face and differing in the topology of the cluster of amino groups at the primary side were selected for this study. All of them compact pEGFP-C3 plasmid DNA and promote transfection in HeLa and MCF-7 cells, both in absence and in presence of human serum...
March 15, 2017: Biochimica et Biophysica Acta
Yang-Yang Lv, Xiao Li, Bin-Bin Zhang, W Y Deng, Shu-Hua Yao, Y B Chen, Jian Zhou, Shan-Tao Zhang, Ming-Hui Lu, Lei Zhang, Mingliang Tian, L Sheng, Yan-Feng Chen
The asymmetric electron dispersion in type-II Weyl semimetal theoretically hosts anisotropic transport properties. Here, we observe the significant anisotropic Adler-Bell-Jackiw (ABJ) anomaly in the Fermi-level delicately adjusted WTe_{1.98} crystals. Quantitatively, C_{W}, a coefficient representing the intensity of the ABJ anomaly along the a and b axis of WTe_{1.98} are 0.030 and 0.051  T^{-2} at 2 K, respectively. We found that the temperature-sensitive ABJ anomaly is attributed to a topological phase transition from a type-II Weyl semimetal to a trivial semimetal, which is verified by a first-principles calculation using experimentally determined lattice parameters at different temperatures...
March 3, 2017: Physical Review Letters
Y Liu, Y J Long, L X Zhao, S M Nie, S J Zhang, Y X Weng, M L Jin, W M Li, Q Q Liu, Y W Long, R C Yu, C Z Gu, F Sun, W G Yang, H K Mao, X L Feng, Q Li, W T Zheng, H M Weng, X Dai, Z Fang, G F Chen, C Q Jin
Recently, theoretical studies show that layered HfTe5 is at the boundary of weak &strong topological insulator (TI) and might crossover to a Dirac semimetal state by changing lattice parameters. The topological properties of 3D stacked HfTe5 are expected hence to be sensitive to pressures tuning. Here, we report pressure induced phase evolution in both electronic &crystal structures for HfTe5 with a culmination of pressure induced superconductivity. Our experiments indicated that the temperature for anomaly resistance peak (Tp) due to Lifshitz transition decreases first before climbs up to a maximum with pressure while the Tp minimum corresponds to the transition from a weak TI to strong TI...
March 16, 2017: Scientific Reports
Chihyun Park, So Jeong Yun, Sung Jin Ryu, Soyoung Lee, Young-Sam Lee, Youngmi Yoon, Sang Chul Park
BACKGROUND: Cellular senescence irreversibly arrests growth of human diploid cells. In addition, recent studies have indicated that senescence is a multi-step evolving process related to important complex biological processes. Most studies analyzed only the genes and their functions representing each senescence phase without considering gene-level interactions and continuously perturbed genes. It is necessary to reveal the genotypic mechanism inferred by affected genes and their interaction underlying the senescence process...
March 15, 2017: BMC Systems Biology
Colm P Kelleher, Rodrigo E Guerra, Andrew D Hollingsworth, Paul M Chaikin
We study the phase behavior of a system of charged colloidal particles that are electrostatically bound to an almost flat interface between two fluids. We show that, despite the fact that our experimental system consists of only 10^{3}-10^{4} particles, the phase behavior is consistent with the theory of melting due to Kosterlitz, Thouless, Halperin, Nelson, and Young. Using spatial and temporal correlations of the bond-orientational order parameter, we classify our samples into solid, isotropic fluid, and hexatic phases...
February 2017: Physical Review. E
Yang-Yang Lv, Lin Cao, Xiao Li, Bin-Bin Zhang, Kang Wang, Bin Pang, Ligang Ma, Dajun Lin, Shu-Hua Yao, Jian Zhou, Y B Chen, Song-Tao Dong, Wenchao Liu, Ming-Hui Lu, Yulin Chen, Yan-Feng Chen
Transition metal dichalcogenides (TMDs) WTe2 and MoTe2 with orthorhombic Td phase, being potential candidates as type-II Weyl semimetals, are attracted much attention recently. Here we synthesized a series of miscible Mo1-xWxTe2 single crystals by bromine vapor transport method. Composition-dependent X-ray diffraction and Raman spectroscopy, as well as composition and temperature-dependent resistivity prove that the tunable crystal structure (from hexagonal (2H), monoclinic (β) to orthorhombic (Td) phase) can be realized by increasing W content in Mo1-xWxTe2...
March 15, 2017: Scientific Reports
Pablo Rodriguez-Lopez, Wilton J M Kort-Kamp, Diego A R Dalvit, Lilia M Woods
The Casimir force is a universal interaction induced by electromagnetic quantum fluctuations between any types of objects. The expansion of the graphene family by adding silicene, germanene and stanene (2D allotropes of Si, Ge, and Sn), lends itself as a platform to probe Dirac-like physics in honeycomb staggered systems in such a ubiquitous interaction. We discover Casimir force phase transitions between these staggered 2D materials induced by the complex interplay between Dirac physics, spin-orbit coupling and externally applied fields...
March 15, 2017: Nature Communications
Mirele Bastos Pinto, Antonio Lenito Soares, Andy Mella Orellana, Helio Anderson Duarte, Heitor Avelino de Abreu
Different polymorphs of the Nb2O5 can be obtained depending on the pressure and temperature of calcination leading to different catalytic properties. Two polymorphs of niobia, T-Nb2O5 and B-Nb2O5 have been investigated by means of density funtional/plane waves method. The equation of state predicted that B-Nb2O5 phase is more stable than the T-Nb2O5 at low temperature and at high pressure both phases are stable in a good agreement with the available experimental data. The calculated cohesive energies of 8.56 and 8...
March 14, 2017: Journal of Physical Chemistry. A
Denis B Kuznetsov, Ekaterina V Orlova, Valery A Neschislyaev, Igor L Volkhin, Igor V Izmestiev, Igor V Lunegov, Alevtina V Balandina, Dina G Dianova
The research investigates the mechanism of microwave radiation effects on biological characteristics and structural-dynamic parameters of a sensor bioluminescence system. The research objects are a sterile growth medium (fish meal hydrolisate) and a bacterial culture. It has been established that irradiation causes changes of the growth medium spectral properties within the range of 200-350nm. Changes take place in the intensity and character of luminescence, as well as in relaxation parameters of nuclear magnetic resonance, growth characteristics of the bacterial culture, its cellular morphology and surface topology...
March 6, 2017: Colloids and Surfaces. B, Biointerfaces
Luting Xu, Xinqi Li, Qingfeng Sun
The Josephson supercurrent through the hybrid Majorana--quantum dot--Majorana junction is investigated. We particularly analyze the effect of spin-selective coupling between the Majorana and quantum dot states, which emerges only in the topological phase and will influence the current through bent junctions and/or in the presence of magnetic fields in the quantum dot. We find that the characteristic behaviors of the supercurrent through this system are quite counterintuitive, remarkably differing from the resonant tunneling, e...
March 13, 2017: Journal of Physics. Condensed Matter: An Institute of Physics Journal
Ya-Xian Fan, Tang-Qing Sang, Ting Liu, Lan-Lan Xu, Zhi-Yong Tao
Interface states can always arise in heterostructures that consist of two or more (artificial) materials with topologically different energy bands. The gapped band structure can be classified by the Chern number (a topological invariant) generally or the Zak phase in one-dimensional periodic systems. Recently, topological properties have been employed to investigate the interface states occurring at the connecting regions of the heterostructures of mechanical isostatic lattices and acoustical waveguides. Here, we study this heterostructure phenomenon by carefully connecting two corrugated stainless steel waveguides with Bragg and non-Bragg gaps at approximately the same frequency...
March 13, 2017: Scientific Reports
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