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Miriam Martinsons, Michael Schmiedeberg
The growth of quasicrystals, i.e., structures with long-range positional order but no periodic translational symmetry, is more complex than the growth of periodic crystals. By employing Brownian dynamics simulations in two dimensions for colloidal particles that interact according to an isotropic pair potential with two incommensurate lengths, we study the growth of quasicrystalline structures by sequentially depositing particles at their surface. We quantify the occurrence of quasicrystalline order as a function of the temperature and the rate of added particles...
May 15, 2018: Journal of Physics. Condensed Matter: An Institute of Physics Journal
Samuel Savitz, Mehrtash Babadi, Ron Lifshitz
For many years, quasicrystals were observed only as solid-state metallic alloys, yet current research is now actively exploring their formation in a variety of soft materials, including systems of macromolecules, nanoparticles and colloids. Much effort is being invested in understanding the thermodynamic properties of these soft-matter quasicrystals in order to predict and possibly control the structures that form, and hopefully to shed light on the broader yet unresolved general questions of quasicrystal formation and stability...
May 1, 2018: IUCrJ
Krzysztof Giergiel, Artur Miroszewski, Krzysztof Sacha
Time crystals are quantum many-body systems that, due to interactions between particles, are able to spontaneously self-organize their motion in a periodic way in time by analogy with the formation of crystalline structures in space in condensed matter physics. In solid state physics properties of space crystals are often investigated with the help of external potentials that are spatially periodic and reflect various crystalline structures. A similar approach can be applied for time crystals, as periodically driven systems constitute counterparts of spatially periodic systems, but in the time domain...
April 6, 2018: Physical Review Letters
Shinji Watanabe, Kazumasa Miyake
To get an insight into a new type of quantum critical phenomena recently discovered in the quasicrystal Yb<sub>15</sub>Al<sub>34</sub>Au<sub>51</sub> and approximant crystal (AC) Yb<sub>14</sub>Al<sub>35</sub>Au<sub>51</sub> under pressure, we discuss the property of the crystalline electronic field (CEF) at Yb in the AC 
 and show that uneven CEF levels at each Yb site can appear because of the Al/Au mixed sites...
March 20, 2018: Journal of Physics. Condensed Matter: An Institute of Physics Journal
Philipp T Dumitrescu, Romain Vasseur, Andrew C Potter
We simulate the dynamics of a disordered interacting spin chain subject to a quasiperiodic time-dependent drive, corresponding to a stroboscopic Fibonacci sequence of two distinct Hamiltonians. Exploiting the recursive drive structure, we can efficiently simulate exponentially long times. After an initial transient, the system exhibits a long-lived glassy regime characterized by a logarithmically slow growth of entanglement and decay of correlations analogous to the dynamics at the many-body delocalization transition...
February 16, 2018: Physical Review Letters
Nikita P Kryuchkov, Stanislav O Yurchenko, Yury D Fomin, Elena N Tsiok, Valentin N Ryzhov
A transition from a square to a hexagonal lattice is studied in a 2D system of particles interacting via a core-softened potential. Due to the presence of two length scales of repulsion, different local configurations with four, five, and six neighbors are possible, leading to the formation of complex crystals. The previously proposed interpolation method is generalized to calculate pair correlations in crystals whose unit cell consists of more than one particle. The high efficiency of the method is illustrated using a snub square lattice as a representative example...
March 14, 2018: Soft Matter
Beth A Lindquist, Ryan B Jadrich, William D Piñeros, Thomas M Truskett
We discuss how a machine learning approach based on relative entropy optimization can be used as an inverse design strategy to discover isotropic pair interactions that self-assemble single- or multicomponent particle systems into Frank-Kasper phases. In doing so, we also gain insights into the self-assembly of quasicrystals.
March 8, 2018: Journal of Physical Chemistry. B
Junpeng Hou, Haiping Hu, Kuei Sun, Chuanwei Zhang
A quasicrystal is a class of ordered structures defying conventional classification of solid crystals and may carry classically forbidden (e.g., fivefold) rotational symmetries. In view of long-sought supersolids, a natural question is whether a superfluid can spontaneously form quasicrystalline order that is not possessed by the underlying Hamiltonian, forming "superfluid-quasicrystals." Here we show that a superfluid-quasicrystal stripe state with the minimal fivefold rotational symmetry can be realized as the ground state of a Bose-Einstein condensate within a practical experimental scheme...
February 9, 2018: Physical Review Letters
Zhiqing Yang, Lifeng Zhang, Matthew F Chisholm, Xinzhe Zhou, Hengqiang Ye, Stephen J Pennycook
Dislocations in crystals naturally break the symmetry of the bulk, introducing local atomic configurations with symmetries such as fivefold rings. But dislocations do not usually nucleate aperiodic structure along their length. Here we demonstrate the formation of extended binary quasicrystalline precipitates with Penrose-like random-tiling structures, beginning with chemical ordering within the pentagonal structure at cores of prismatic dislocations in Mg-Zn alloys. Atomic resolution observations indicate that icosahedral chains centered along [0001] pillars of Zn interstitial atoms are formed templated by the fivefold rings at dislocation cores...
February 23, 2018: Nature Communications
Daniel C Fredrickson
The structural diversity of intermetallic phases poses a great challenge to chemical theory and materials design. In this Account, two examples are used to illustrate how a focus on the most complex of these structures (and their relationships to simpler ones) can reveal how chemical principles underlie structure for broad families of compounds. First, we show how experimental investigations into the Fe-Al-Si system, inspired by host-guest like features in the structure of Fe25 Al78 Si20 , led to a theoretical approach to deriving isolobal analogies between molecular and intermetallic compounds and a more general electron counting rule...
February 20, 2018: Accounts of Chemical Research
Ryan D Brown, Steven A Corcelli, S Alex Kandel
Traditionally, the goal of self-assembly and supramolecular chemistry is to engineer an equilibrium structure with a desired geometry and functionality; this is achieved through careful choice of molecular monomers, growth conditions, and substrate. Supramolecular assemblies produced under nonequilibrium conditions, in contrast, can form metastable structures with conformations quite different from those accessible in equilibrium self-assembly. The study of nonequilibrium growth of clusters potentially impacts the study of nucleation in atmospheric aerosols, nucleation in organic crystallization, and mesoscale organization for systems ranging from biological molecules to molecular electronics...
February 20, 2018: Accounts of Chemical Research
M Schmiedeberg, C V Achim, J Hielscher, S C Kapfer, H Löwen
We explore the growth of two-dimensional quasicrystals, i.e., aperiodic structures that possess long-range order, from two seeds at various distances and with different orientations by using dynamical phase-field crystal calculations. We compare the results to the growth of periodic crystals from two seeds. There, a domain border consisting of dislocations is observed in case of large distances between the seed and large angles between their orientation. Furthermore, a domain border is found if the seeds are placed at a distance that does not fit to the periodic lattice...
July 2017: Physical Review. E
K Kamiya, T Takeuchi, N Kabeya, N Wada, T Ishimasa, A Ochiai, K Deguchi, K Imura, N K Sato
Superconductivity is ubiquitous as evidenced by the observation in many crystals including carrier-doped oxides and diamond. Amorphous solids are no exception. However, it remains to be discovered in quasicrystals, in which atoms are ordered over long distances but not in a periodically repeating arrangement. Here we report electrical resistivity, magnetization, and specific-heat measurements of Al-Zn-Mg quasicrystal, presenting convincing evidence for the emergence of bulk superconductivity at a very low transition temperature of [Formula: see text] K...
January 11, 2018: Nature Communications
Joyce Pham, Fanqiang Meng, Matthew J Lynn, Tao Ma, Andreas Kreyssig, Matthew J Kramer, Alan I Goldman, Gordon J Miller
The irreversible transformation from an icosahedral quasicrystal (i-QC) CaAu4.39 Al1.61 to its cubic 2/1 crystalline approximant (CA) Ca13 Au56.31(3) Al21.69 (CaAu4.33(1) Al1.67 , Pa3̅ (No. 205); Pearson symbol: cP728; a = 23.8934(4)), starting at ∼570 °C and complete by ∼650 °C, is discovered from in situ, high-energy, variable-temperature powder X-ray diffraction (PXRD), thereby providing direct experimental evidence for the relationship between QCs and their associated CAs. The new cubic phase crystallizes in a Tsai-type approximant structure under the broader classification of polar intermetallic compounds, in which atoms of different electronegativities, viz...
January 31, 2018: Journal of the American Chemical Society
Qisheng Lin, Gordon J Miller
Intermetallic compounds represent an extensive pool of candidates for energy related applications stemming from magnetic, electric, optic, caloric, and catalytic properties. The discovery of novel intermetallic compounds can enhance understanding of the chemical principles that govern structural stability and chemical bonding as well as finding new applications. Valence electron-poor polar intermetallics with valence electron concentrations (VECs) between 2.0 and 3.0 e- /atom show a plethora of unprecedented and fascinating structural motifs and bonding features...
January 16, 2018: Accounts of Chemical Research
Insung Han, Xianghui Xiao, Ashwin J Shahani
How does a quasicrystal grow? Despite the decades of research that have been dedicated to this area of study, it remains one of the fundamental puzzles in the field of crystal growth. Although there has been no lack of theoretical studies on quasicrystal growth, there have been very few experimental investigations with which to test their various hypotheses. In particular, evidence of the in situ and three-dimensional (3D) growth of a quasicrystal from a parent liquid phase is lacking. To fill-in-the-gaps in our understanding of the solidification and melting pathways of quasicrystals, we performed synchrotron-based X-ray imaging experiments on a decagonal phase with composition of Al-15at%Ni-15at%Co...
December 12, 2017: Scientific Reports
Mengjie Zu, Peng Tan, Ning Xu
In traditional approaches to form quasicrystals, multiple competing length scales involved in particle size, shape, or interaction potential are believed to be necessary. It is unexpected that quasicrystals can be formed by monodisperse, isotropic particles interacting via a simple potential that does not contain explicit multiple length scales to stabilize quasicrystals. Here, we report the surprising finding of the formation of such quasicrystals in high-density systems of soft-core particles. Although there are length scales naturally introduced in our model systems, they do not establish the quasicrystalline order...
December 12, 2017: Nature Communications
A Dareau, E Levy, M Bosch Aguilera, R Bouganne, E Akkermans, F Gerbier, J Beugnon
Topological properties of crystals and quasicrystals is a subject of recent and growing interest. This Letter reports an experiment where, for certain quasicrystals, these properties can be directly retrieved from diffraction. We directly observe, using an interferometric approach, all of the topological invariants of finite-length Fibonacci chains in their diffraction pattern. We also quantitatively demonstrate the stability of these topological invariants with respect to structural disorder.
November 24, 2017: Physical Review Letters
Julius Oppenheim, Chi Ma, Jinping Hu, Luca Bindi, Paul J Steinhardt, Paul D Asimow
Five-component icosahedral quasicrystals with compositions in the range Al68-73 Fe11-16 Cu10-12 Cr1-4 Ni1-2 were recently recovered after shocking metallic CuAl5 and (Mg0.75 Fe0.25 )2 SiO4 olivine in a stainless steel 304 chamber, intended to replicate a natural shock that affected the Khatyrka meteorite. The iron in those quasicrystals might have originated either from reduction of Fe2+ in olivine or from the stainless steel chamber. In this study, we clarify the shock synthesis mechanism of icosahedral quasicrystals through two new shock recovery experiments...
November 15, 2017: Scientific Reports
J Oppenheim, C Ma, J Hu, L Bindi, P J Steinhardt, P D Asimow
The Khatyrka meteorite contains both icosahedral and decagonal quasicrystals. In our previous studies, icosahedral quasicrystals have been synthesized and recovered from shock experiments at the interface between CuAl5 and stainless steel 304 alloys. In this study, we report a new shock recovery experiment aimed at synthesizing decagonal quasicrystals similar to decagonite, natural Al71 Ni24 Fe5 . Aluminum 2024 and permalloy 80 alloys were stacked together and shocked in a stainless steel 304 recovery chamber...
November 15, 2017: Scientific Reports
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