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"topological phase"

Svitlana Kondovych, Igor Luk'yanchuk, Tatyana I Baturina, Valerii M Vinokur
The two-dimensional (2D) logarithmic character of Coulomb interaction between charges and the resulting logarithmic confinement is a remarkable inherent property of high dielectric constant (high-κ) thin films with far reaching implications. Most and foremost, this is the charge Berezinskii-Kosterlitz-Thouless transition with the notable manifestation, low-temperature superinsulating topological phase. Here we show that the range of the confinement can be tuned by the external gate electrode and unravel a variety of electrostatic interactions in high-k films...
February 20, 2017: Scientific Reports
M Barrio, J Huguet, I B Rietveld, B Robert, R Céolin, J Ll Tamarit
Understanding the polymorphic behavior of active pharmaceutical ingredients is important for formulation purposes and regulatory reasons. Metacetamol is an isomer of paracetamol and it similarly exhibits polymorphism. In the present paper, it has been found that one of the polymorphs of metacetamol is only stable under increased pressure, which has led to the conclusion that metacetamol like paracetamol is a monotropic system under ordinary (= laboratory) conditions and that it becomes enantiotropic under pressure with the I-II-L triple point coordinates for metacetamol TI-II-L = 535±10 K and PI-II-L = 692±70 MPa...
February 9, 2017: Journal of Pharmaceutical Sciences
Maciej Bieniek, Tomasz Woźniak, Paweł Potasz
We investigate electronic and transport properties of bismuth (111) bilayer in the context of stability of its topological properties against different perturbations. The effects of spin-orbit coupling variations, geometry relaxation and an interaction with a substrate are considered. Transport properties are studied in the presence of Anderson disorder. Band structure calculations are performed within multi-orbital tight-binding model and density functional theory methods. A band inversion process in bismuth (111) infinite bilayer and an evolution of edge states dispersion in ribbons as a function of spin-orbit coupling strength are analyzed...
February 6, 2017: Journal of Physics. Condensed Matter: An Institute of Physics Journal
R Céolin, I B Rietveld
Cimetidine is a histamine H2-receptor antagonist used against peptic ulcers. It is known to exhibit crystalline polymorphism. Forms A and D melt within 0.35 degrees from each other and the enthalpies of fusion are similar as well. The present paper demonstrates how to construct a pressure-temperature phase diagram with only calorimetric and volumetric data available. The phase diagram provides the stability domains and the phase equilibria for the phases A, D, the liquid and the vapor. Cimetidine is overall monotropic with form D the only stable solid phase...
March 2017: Annales Pharmaceutiques Françaises
Yunhua Wang, Yulan Liu, Biao Wang
Periodically driven nontrivial quantum states open another door to engineer topological phases in solid systems by light. Here we show, based on the Floquet-Bloch theory, that the on-resonant linearly and circularly polarized infrared light brings in the exotic Floquet quantum spin Hall state and half-metal in two-dimensional Metal-organic frameworks (2D MOFs) because of the unbroken and broken time-reversal symmetry, respectively. We also observe that the off-resonant light triggers topological quantum phase transitions and induces semimetals with pseudospin-1 Dirac-Weyl fermions via the photon-dressed topological band structures of 2D MOFs...
January 30, 2017: Scientific Reports
Kai-Wei Chang, Wei Ji, Chao-Cheng Kaun
The way in which states of a topological insulator (TI) transform from monolayer to bulk is an important issue for applications in spintronics. However, unlike graphite, most layered materials are difficult to exfoliate. Using first-principles calculations, we predict that thallium selenide (TlSe) will be a layered TI with rather weak interlayer coupling and thus it should be exfoliated easily. The evolution of the topological states can also be driven by doping with indium (In) atoms or applying lateral strains...
February 1, 2017: Physical Chemistry Chemical Physics: PCCP
Xiaoming Cai
We study the competition of disorder and superconductivity for a generalized Kitaev model in incommensurate potentials. The generalized Kitaev model describes one dimensional spinless fermions with long-range p-wave superconducting pairing, which decays with distance l as a power law  ∼[Formula: see text]. We focus on the transition from the topological superconducting phase to the topologically trivial Anderson localized phase, and effects of the exponent α on this phase transition. In the topological superconducting phase, for a system under open boundary condition the amplitude of zero-mode Majorana fermion has a hybrid exponential-algebraic decay as the distance increases from the edge...
March 22, 2017: Journal of Physics. Condensed Matter: An Institute of Physics Journal
M Hyla
Network-forming As2(S/Se)m nanoclusters are employed to recognize expected variations in a vicinity of some remarkable compositions in binary As-Se/S glassy systems accepted as signatures of optimally constrained intermediate topological phases in earlier temperature-modulated differential scanning calorimetry experiments. The ab initio quantum chemical calculations performed using the cation-interlinking network cluster approach show similar oscillating character in tendency to local chemical decomposition but obvious step-like behavior in preference to global phase separation on boundary chemical compounds (pure chalcogen and stoichiometric arsenic chalcogenides)...
December 2017: Nanoscale Research Letters
Morten Amundsen, Jabir Ali Ouassou, Jacob Linder
Multiterminal Josephson junctions have recently been proposed as a route to artificially mimic topological matter with the distinct advantage that its properties can be controlled via the superconducting phase difference, giving rise to Weyl points in 4-terminal geometries. A key goal is to accurately determine when the system makes a transition from a gapped to non-gapped state as a function of the phase differences in the system, the latter effectively playing the role of quasiparticle momenta in conventional topological matter...
January 17, 2017: Scientific Reports
Sergey Kruk, Alexey Slobozhanyuk, Denitza Denkova, Alexander Poddubny, Ivan Kravchenko, Andrey Miroshnichenko, Dragomir Neshev, Yuri Kivshar
Recently introduced field of topological photonics aims to explore the concepts of topological insulators for novel phenomena in optics. Here polymeric chains of subwavelength silicon nanodisks are studied and it is demonstrated that these chains can support two types of topological edge modes based on magnetic and electric Mie resonances, and their topological properties are fully dictated by the spatial arrangement of the nanoparticles in the chain. It is observed experimentally and described how theoretically topological phase transitions at the nanoscale define a change from trivial to nontrivial topological states when the edge mode is excited...
January 12, 2017: Small
John Mangeri, Yomery Espinal, Andrea Jokisaari, S Pamir Alpay, Serge Nakhmanson, Olle Heinonen
Composite materials comprised of ferroelectric nanoparticles in a dielectric matrix are being actively investigated for a variety of functional properties attractive for a wide range of novel electronic and energy harvesting devices. However, the dependence of these functionalities on shapes, sizes, orientation and mutual arrangement of ferroelectric particles is currently not fully understood. In this study, we utilize a time-dependent Ginzburg-Landau approach combined with coupled-physics finite-element-method based simulations to elucidate the behavior of polarization in isolated spherical PbTiO3 or BaTiO3 nanoparticles embedded in a dielectric medium, including air...
January 11, 2017: Nanoscale
Jayita Nayak, Shu-Chun Wu, Nitesh Kumar, Chandra Shekhar, Sanjay Singh, Jörg Fink, Emile E D Rienks, Gerhard H Fecher, Stuart S P Parkin, Binghai Yan, Claudia Felser
The rare-earth monopnictide LaBi exhibits exotic magneto-transport properties, including an extremely large and anisotropic magnetoresistance. Experimental evidence for topological surface states is still missing although band inversions have been postulated to induce a topological phase in LaBi. In this work, we have revealed the existence of surface states of LaBi through the observation of three Dirac cones: two coexist at the corners and one appears at the centre of the Brillouin zone, by employing angle-resolved photoemission spectroscopy in conjunction with ab initio calculations...
January 9, 2017: Nature Communications
Jianpeng Liu, Se Young Park, Kevin F Garrity, David Vanderbilt
We study adatom-covered single layers of CrSiTe_{3} and CrGeTe_{3} using first-principles calculations based on hybrid functionals. We find that the insulating ground state of a monolayer of La (Lu) deposited on single-layer CrSiTe_{3} (CrGeTe_{3}) carries spontaneously generated current loops around the Cr sites. These "flux states" induce antiferromagnetically ordered orbital moments on the Cr sites and are also associated with nontrivial topological properties. The calculated Chern numbers for these systems are predicted to be ±1 even in the absence of spin-orbit coupling, with sizable gaps on the order of 100 meV...
December 16, 2016: Physical Review Letters
Mazhar N Ali, Leslie M Schoop, Chirag Garg, Judith M Lippmann, Erik Lara, Bettina Lotsch, Stuart S P Parkin
Magnetoresistance (MR), the change of a material's electrical resistance in response to an applied magnetic field, is a technologically important property that has been the topic of intense study for more than a quarter century. We report the observation of an unusual "butterfly"-shaped titanic angular magnetoresistance (AMR) in the nonmagnetic Dirac material, ZrSiS, which we find to be the most conducting sulfide known, with a 2-K resistivity as low as 48(4) nΩ⋅cm. The MR in ZrSiS is large and positive, reaching nearly 1...
December 2016: Science Advances
Peng-Fei Liu, Liujiang Zhou, Thomas Frauenheim, Li-Ming Wu
Based on first-principles calculations, we predict the existence of the quantum spin Hall (QSH) effect in hydrogenated transition-metal nitrides MN2H2 (M = Mo, W), showing high structural stability. MN2H2 monolayers are identified to be intrinsic topological insulators (TIs) with protected Dirac type topological helical edge states, and show robust topological features against the large stretching strain. Besides, sizeable intrinsic nontrivial band gaps (70-124 meV) ensure the QSH effect in MN2H2 at room temperature...
January 19, 2017: Nanoscale
Gabriel Antonius, Steven G Louie
Contrary to previous two-band model studies which find increasing temperature would induce a topological phase transition, we show here through first-principles calculations that the opposite is also realizable, depending on the material's full band structure and symmetry of the electron-phonon coupling potential. This finding explains recent experimental results by Wojek et al. [Nat. Commun. 6, 8463 (2015)NCAOBW2041-172310.1038/ncomms9463]. We show that the topological phase diagram of BiTl(S_{1-δ}Se_{δ})_{2} as a function of doping and temperature contains two distinct regions with nontrivial topology...
December 9, 2016: Physical Review Letters
Eric J Meier, Fangzhao Alex An, Bryce Gadway
The Su-Schrieffer-Heeger (SSH) model, which captures the most striking transport properties of the conductive organic polymer trans-polyacetylene, provides perhaps the most basic model system supporting topological excitations. The alternating bond pattern of polyacetylene chains is captured by the bipartite sublattice structure of the SSH model, emblematic of one-dimensional chiral symmetric topological insulators. This structure supports two distinct nontrivial topological phases, which, when interfaced with one another or with a topologically trivial phase, give rise to topologically protected, dispersionless boundary states...
December 23, 2016: Nature Communications
M T Deng, S Vaitiekėnas, E B Hansen, J Danon, M Leijnse, K Flensberg, J Nygård, P Krogstrup, C M Marcus
Hybrid nanowires combining semiconductor and superconductor materials appear well suited for the creation, detection, and control of Majorana bound states (MBSs). We demonstrate the emergence of MBSs from coalescing Andreev bound states (ABSs) in a hybrid InAs nanowire with epitaxial Al, using a quantum dot at the end of the nanowire as a spectrometer. Electrostatic gating tuned the nanowire density to a regime of one or a few ABSs. In an applied axial magnetic field, a topological phase emerges in which ABSs move to zero energy and remain there, forming MBSs...
December 23, 2016: Science
Wei Qin, Di Xiao, Kai Chang, Shun-Qing Shen, Zhenyu Zhang
Normal superconductors with Rashba spin-orbit coupling have been explored as candidate systems of topological superconductors. Here we present a comparative theoretical study of the effects of different types of disorder on the topological phases of two-dimensional Rashba spin-orbit coupled superconductors. First, we show that a topologically trivial superconductor can be driven into a chiral topological superconductor upon diluted doping of isolated magnetic disorder, which close and reopen the quasiparticle gap of the paired electrons in a nontrivial manner...
December 19, 2016: Scientific Reports
Muhammad Imran Afzal, Yong Tak Lee
Von Neumann and Wigner theorized the bounding and anti-crossing of eigenstates. Experiments have demonstrated that owing to anti-crossing and similar radiation rates, the graphene-like resonance of inhomogeneously strained photonic eigenstates can generate a pseudomagnetic field, bandgaps and Landau levels, whereas exponential or dissimilar rates induce non-Hermicity. Here, we experimentally demonstrate higher-order supersymmetry and quantum phase transitions by resonance between similar one-dimensional lattices...
December 14, 2016: Scientific Reports
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