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Wolf Widdra - One of the best experts on this subject based on the ideXlab platform.
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electronic band structure of a two dimensional oxide quasicrystal
Physical Review B, 2019Co-Authors: Stefan Forster, Chengtien Chiang, Martin Ellguth, Florian O Schumann, C Tusche, Richard Kraska, Wolf WiddraAbstract:Since the discovery of Quasicrystals, the study of their electronic structure has been a challenging topic due to the absence of translational symmetry. Here, the valence bands of a novel two-dimensional ultrathin BaTiO${}_{3}$-derived oxide quasicrystal are determined by momentum-resolved photoelectron spectroscopy. The dispersion of the oxygen 2$p$ bands and the occupation of the Ti 3$d$ states are identified. They bridge the knowledge deriving from free-electron-like wave functions in bulk Quasicrystals to that of the more localized electrons in confined dimensions.
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quasicrystalline structure formation in a classical crystalline thin film system
Nature, 2013Co-Authors: Stefan Forster, K Meinel, Rene Hammer, Martin Trautmann, Wolf WiddraAbstract:The unusual ordering of Quasicrystals can be induced in thin films of a regular crystalline material; here a two-dimensional quasicrystal has been achieved by growing thin films of the perovskite barium titanate on an appropriately oriented crystalline platinum substrate. Quasicrystals are quite distinct from conventional crystals: their component parts are ordered, but they do not display the precise repeating patterns seen in crystals. These unusual structures can give Quasicrystals novel — and potentially useful — properties. Quasicrystallinity is rare, restricted to a few specific materials, but Wolf Widdra and co-workers now show that quasicrystallinity can be induced in thin films of a regular crystalline material by exploiting the geometric mismatch between two different periodic systems. Specifically, they find that thin perovskite films made of barium titanate can be driven to adopt a quasicrystalline dodecahedral structure when grown on an appropriately oriented crystalline platinum substrate. Further development of this methodology might bring the concept of quasicrystallinity to a wider range of materials and technical applications. The discovery of Quasicrystals1—crystalline structures that show order while lacking periodicity—forced a paradigm shift in crystallography. Initially limited to intermetallic systems1,2,3,4, the observation of quasicrystalline structures has recently expanded to include ‘soft’ Quasicrystals in the fields of colloidal and supermolecular chemistry5,6,7,8,9. Here we report an aperiodic oxide that grows as a two-dimensional quasicrystal on a periodic single-element substrate. On a Pt(111) substrate with 3-fold symmetry, the perovskite barium titanate BaTiO3 forms a high-temperature interface-driven structure with 12-fold symmetry. The building blocks of this dodecagonal structure assemble with the theoretically predicted Stampfli–Gahler tiling10,11 having a fundamental length-scale of 0.69 nm. This example of interface-driven formation of ultrathin Quasicrystals from a typical periodic perovskite oxide potentially extends the quasicrystal concept to a broader range of materials. In addition, it demonstrates that frustration at the interface between two periodic materials can drive a thin film into an aperiodic quasicrystalline phase, as proposed previously12. Such structures might also find use as ultrathin buffer layers for the accommodation of large lattice mismatches in conventional epitaxy13.
Mordechai Segev - One of the best experts on this subject based on the ideXlab platform.
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topological photonic Quasicrystals fractal topological spectrum and protected transport
Physical Review X, 2016Co-Authors: Miguel A Bandres, Mikael C Rechtsman, Mordechai SegevAbstract:Quasicrystals are a class of materials that exhibit long-range order but no periodicity. A study of topological transport in Quasicrystals shows that, surprisingly, a two-dimensional photonic quasicrystal exhibits a topological insulating phase.
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Phason dynamics in nonlinear photonic Quasicrystals.
Nature materials, 2007Co-Authors: Barak Freedman, Ron Lifshitz, Jason W. Fleischer, Mordechai SegevAbstract:We study the dynamics of phasons in a nonlinear photonic quasicrystal. The photonic quasicrystal is formed by optical induction, and its dynamics is initiated by allowing the light waves inducing the quasicrystal to nonlinearly interact with one another. We show quantitatively that, when phason strain is introduced in a controlled manner, it relaxes through the nonlinear interactions within the photonic quasicrystal. We establish experimentally that the relaxation rate of phason strain in the quasicrystal is substantially lower than the relaxation rate of phonon strain, as predicted for atomic Quasicrystals. Finally, we monitor and identify individual ‘atomic-scale’ phason flips occurring in the photonic quasicrystal as its phason strain relaxes, as well as noise-induced phason fluctuations.
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wave and defect dynamics in nonlinear photonic Quasicrystals
Nature, 2006Co-Authors: Barak Freedman, Ron Lifshitz, Mordechai Segev, Guy Bartal, Demetrios N Christodoulides, Jason W. FleischerAbstract:A photonic equivalent of a quasicrystal is created in which wave and defect dynamics can be made visible — for example, it is shown that a dislocation introduced in the photonic quasicrystal is healed by re-arrangements of the lattice. Quasicrystals are unique structures with long-range order but no periodicity. Their properties have intrigued scientists ever since their discovery1 and initial theoretical analysis2,3. The lack of periodicity excludes the possibility of describing quasicrystal structures with well-established analytical tools, including common notions like Brillouin zones and Bloch's theorem. New and unique features such as fractal-like band structures4,5,6,7 and ‘phason’ degrees of freedom8 are introduced. In general, it is very difficult to directly observe the evolution of electronic waves in solid-state atomic Quasicrystals, or the dynamics of the structure itself. Here we use optical induction9,10,11 to create two-dimensional photonic Quasicrystals, whose macroscopic nature allows us to explore wave transport phenomena. We demonstrate that light launched at different quasicrystal sites travels through the lattice in a way equivalent to quantum tunnelling of electrons in a quasiperiodic potential. At high intensity, lattice solitons are formed. Finally, we directly observe dislocation dynamics when crystal sites are allowed to interact with each other. Our experimental results apply not only to photonics, but also to other quasiperiodic systems such as matter waves in quasiperiodic traps12, generic pattern-forming systems as in parametrically excited surface waves13, liquid Quasicrystals14, and the more familiar atomic Quasicrystals.
Sharon C. Glotzer - One of the best experts on this subject based on the ideXlab platform.
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entropic formation of a thermodynamically stable colloidal quasicrystal with negligible phason strain
Proceedings of the National Academy of Sciences of the United States of America, 2021Co-Authors: Sangmin Lee, Michael Engel, Erin G Teich, Sharon C. GlotzerAbstract:Quasicrystals have been discovered in a variety of materials ranging from metals to polymers. Yet, why and how they form is incompletely understood. In situ transmission electron microscopy of alloy quasicrystal formation in metals suggests an error-and-repair mechanism, whereby quasiperiodic crystals grow imperfectly with phason strain present, and only perfect themselves later into a high-quality quasicrystal with negligible phason strain. The growth mechanism has not been investigated for other types of Quasicrystals, such as dendrimeric, polymeric, or colloidal Quasicrystals. Soft-matter Quasicrystals typically result from entropic, rather than energetic, interactions, and are not usually grown (either in laboratories or in silico) into large-volume Quasicrystals. Consequently, it is unknown whether soft-matter Quasicrystals form with the high degree of structural quality found in metal alloy Quasicrystals. Here, we investigate the entropically driven growth of colloidal dodecagonal Quasicrystals (DQCs) via computer simulation of systems of hard tetrahedra, which are simple models for anisotropic colloidal particles that form a quasicrystal. Using a pattern recognition algorithm applied to particle trajectories during DQC growth, we analyze phason strain to follow the evolution of quasiperiodic order. As in alloys, we observe high structural quality; DQCs with low phason strain crystallize directly from the melt and only require minimal further reduction of phason strain. We also observe transformation from a denser approximant to the DQC via continuous phason strain relaxation. Our results demonstrate that soft-matter Quasicrystals dominated by entropy can be thermodynamically stable and grown with high structural quality––just like their alloy quasicrystal counterparts.
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Non-Close-Packed Three-Dimensional Quasicrystals
Journal of physics. Condensed matter : an Institute of Physics journal, 2017Co-Authors: Pablo F. Damasceno, Sharon C. Glotzer, Michael EngelAbstract:Quasicrystals are frequently encountered in condensed matter. They are important candidates for equilibrium phases from the atomic scale to the nanoscale. Here, we investigate the computational self-assembly of four Quasicrystals in a single model system of identical particles interacting with a tunable isotropic pair potential. We reproduce a known icosahedral quasicrystal and report a decagonal quasicrystal, a dodecagonal quasicrystal, and an octagonal quasicrystal. The Quasicrystals have low coordination number or occur in systems with mesoscale density variations. We also report a network gel phase.
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Computational prediction of an icosahedral quasicrystal
Acta Crystallographica Section A Foundations and Advances, 2014Co-Authors: Michael Engel, Pablo F. Damasceno, Carolyn L. Phillips, Sharon C. GlotzerAbstract:From the first quasicrystal discovered in the laboratory 30 years ago to the only known specimen of naturally occurring Quasicrystals, Quasicrystals with icosahedral symmetry have received great attention. There are more than one hundred stable icosahedral Quasicrystals in metallic alloys; all are identified by their diffraction spectra. Despite this abundance, resolving the positions of the atoms within the solid has been possible only indirectly. Moreover, unlike dodecagonal and other axial Quasicrystals, icosahedral Quasicrystals have been observed neither in simulations nor in non-atomic (e.g. micellar or colloidal) systems, where real-space information would be available. Here we present an icosahedral quasicrystal discovered in computer simulation via self-assembly from the liquid phase. We provide a structure model by analyzing atomic surfaces and report the presence of phason flips. Our results constitute a direct microscopic confirmation of the higher-dimensional crystallographic description of icosahedral Quasicrystals.
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How do Quasicrystals Grow
Physical review letters, 2007Co-Authors: Aaron S. Keys, Sharon C. GlotzerAbstract:Using molecular simulations, we show that the aperiodic growth of Quasicrystals is controlled by the ability of the growing quasicrystal nucleus to incorporate kinetically trapped atoms into the solid phase with minimal rearrangement. In the system under investigation, which forms a dodecagonal quasicrystal, we show that this process occurs through the assimilation of stable icosahedral clusters by the growing quasicrystal. Our results demonstrate how local atomic interactions give rise to the long-range aperiodicity of Quasicrystals.
A.p. Tsai - One of the best experts on this subject based on the ideXlab platform.
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direct observation of growth and stability of al cu fe quasicrystal thin films
Social Science Research Network, 2019Co-Authors: Hadi Parsamehr, A.p. Tsai, Chunliang Yang, Weiting Liu, Shiwei Chen, Shouyi Chang, Lihjuann Chen, Chihhuang LaiAbstract:Al-Cu-Fe based quasicrystal thin films exhibit unique surface and mechanical properties. To better understand the formation of the quasicrystal thin films, we observe direct growth of Quasicrystals, prepared in a multilayer Al-Cu-Fe thin films with subsequent heat treatment, by in-situ synchrotron x-ray diffraction and in-situ transmission electron microscopy during heating and cooling. Using these two methods, we show that the ternary phase is more thermodynamically stable compared to the binary phases at temperature higher than 470 °C during the heating process, and quasicrystal formation occurs during the cooling process, specifically at 660 °C, after the sample has reached a liquid state. To distinguish quasicrystal from approximant crystals in the obtained thin film samples, we use high resolution x-ray diffraction to analyze the sample at room temperature. We reveal that the peak broadening increases monotonically along the twofold, threefold, and fivefold high-symmetry directions with the physical scattering vector but does not have systematic dependence on the phason momentum, which suggests that the thin film sample is indeed a quasicrystal instead of approximant crystals and it is almost free of phason strain. Our study provides a complete understanding of the growth mechanism for thin film Al-Cu-Fe Quasicrystals, which is of particular importance for developing versatile applications of quasicrystal thin films.
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a stable binary quasicrystal
Nature, 2000Co-Authors: A.p. Tsai, J Q Guo, Eiji Abe, Hiroyuki Takakura, Taku J SatoAbstract:All stable Quasicrystals known so far are composed of at least three metallic elements1,2,3,4. Sixteen years after the discovery of the quasicrystal5, we describe a stable binary quasicrystalline alloy in a cadmium–ytterbium (Cd–Yb) system. The structure of this alloy represents a new class of packing of 66-atom icosahedral clusters whose internal structure breaks the icosahedral symmetry. The binary quasicrystal offers a new opportunity to investigate the relation between thermodynamic stability and quasiperiodic structure, as well as providing a basis for the construction of crystallographic models.
Tsutomu Ishimasa - One of the best experts on this subject based on the ideXlab platform.
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Discovery of superconductivity in quasicrystal
Nature communications, 2018Co-Authors: K. Kamiya, Tsutomu Ishimasa, Kazuhiko Deguchi, Tsunehiro Takeuchi, Noriyuki Kabeya, N. Wada, Akira Ochiai, Keiichiro Imura, Noriaki K. SatoAbstract: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. We also find superconductivity in its approximant crystals, structures that are periodic, but that are very similar to Quasicrystals. These observations demonstrate that the effective interaction between electrons remains attractive under variation of the atomic arrangement from periodic to quasiperiodic one. The discovery of the superconducting quasicrystal, in which the fractal geometry interplays with superconductivity, opens the door to a new type of superconductivity, fractal superconductivity.
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quantum critical state in a magnetic quasicrystal
arXiv: Strongly Correlated Electrons, 2012Co-Authors: Kazuhiko Deguchi, Hiroyuki Takakura, Shuya Matsukawa, N Sato, Taisuke Hattori, Kenji Ishida, Tsutomu IshimasaAbstract:Quasicrystals are metallic alloys that possess long-range, aperiodic structures with diffraction symmetries forbidden to conventional crystals. Since the discovery of Quasicrystals by Schechtman et al. at 1984 (ref. 1), there has been considerable progress in resolving their geometric structure. For example, it is well known that the golden ratio of mathematics and art occurs over and over again in their crystal structure. However, the characteristic properties of the electronic states - whether they are extended as in periodic crystals or localized as in amorphous materials - are still unresolved. Here we report the first observation of quantum (T = 0) critical phenomena of the Au-Al-Yb quasicrystal - the magnetic susceptibility and the electronic specific heat coefficient arising from strongly correlated 4f electrons of the Yb atoms diverge as T -> 0. Furthermore, we observe that this quantum critical phenomenon is robust against hydrostatic pressure. By contrast, there is no such divergence in a crystalline approximant, a phase whose composition is close to that of the quasicrystal and whose unit cell has atomic decorations (that is, icosahedral clusters of atoms) that look like the quasicrystal. These results clearly indicate that the quantum criticality is associated with the unique electronic state of the quasicrystal, that is, a spatially confined critical state. Finally we discuss the possibility that there is a general law underlying the conventional crystals and the Quasicrystals.
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Lattice dynamics of the Zn–Mg–Sc icosahedral quasicrystal and its Zn–Sc periodic 1/1 approximant
Nature Materials, 2007Co-Authors: Marc De Boissieu, Tsutomu Ishimasa, Sonia Francoual, Marek Mihalkovič, Kaoru Shibata, Alfred Q. R. Baron, Yvan Sidis, Thomas Lograsso, Louis-pierre Regnault, Franz GählerAbstract:Quasicrystals are long-range-ordered materials that lack translational invariance, so the study of their physical properties remains a challenging problem. Here, we have carried out inelastic-X-ray- and neutron-scattering experiments on single-grain samples of the Zn–Mg–Sc icosahedral quasicrystal and of the Zn–Sc periodic cubic 1/1 approximant, with the aim of studying the respective influence of the local order and of the long-range order (periodic or quasiperiodic) on lattice dynamics. Besides the overall similarities and the existence of a pseudo-gap in the transverse dispersion relation, marked differences are observed, the pseudo-gap being larger and better defined in the approximant than in the quasicrystal. This can be qualitatively explained using the concept of a pseudo-Brillouin-zone in the quasicrystal. These results are compared with simulations on atomic models and using oscillating pair potentials, and the simulations reproduce in detail the experimental results. This paves the way for a detailed understanding of the physics of Quasicrystals.
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Search and Synthesis of New Family of Quasicrystals
MRS Proceedings, 2003Co-Authors: Tsutomu Ishimasa, Shiro Kashimoto, Ryo MaezawaAbstract:Starting from the Zn 17 Sc 3 cubic approximant, new icosahedral quasicrystal was searched by substituting Zn by other metals, M, at the alloy composition of Zn 75 M 10 Sc 15 . In the cases of M = Mn, Fe, Co, Ni, Pd, Pt, Ag and Au, new P-type Quasicrystals were discovered in as-cast alloys. In the cases of M = Fe, Co, Ni, Pd and Ag, the Quasicrystals are thermodynamically stable at approximately 700 °C. This result indicates that use of an approximant crystal as a starting material is very efficient way to search new quasicrystal alloy, and many kinds of metals stabilize the quasicrystal structures; i.e. noble metals and transition elements including Mn, Fe, Co and Ni in addition to Mg. Taking the variety in base metals of Tsai-type approximants into account, this variety in additional components suggests many possibilities of undiscovered Quasicrystals. The equality ofthe electron concentration, ela ≈ 2.1, in Hume-Rothery rule may be a guide to these Quasicrystals.
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A Zn-based icosahedral quasicrystal classified into the same structure type as Cd-based icosahedral Quasicrystals?
Journal of Alloys and Compounds, 2002Co-Authors: Tsutomu Ishimasa, Yasushi Kaneko, Hiroshi KanekoAbstract:Abstract New icosahedral Quasicrystals have been discovered in Zn–Mg–Sc and Zn–Mg–Ti alloy systems. The former forms at the alloy composition of Zn80Mg5Sc15, and belongs to P-type (aP=0.7111 nm) showing high degree of structural perfection. The icosahedral atomic cluster included in 1/1 approximant crystal, Zn17Sc3, suggests that the Zn–Mg–Sc icosahedral quasicrystal has structural similarity to the Cd-based icosahedral Quasicrystals recently reported. Preliminary study of Zn–Mg–Ti alloys has revealed that two types of icosahedral Quasicrystals form near the alloy composition of Zn84Mg8Ti8; namely P-type icosahedral quasicrystal with aP=0.7023 nm, and F-type icosahedral quasicrystal exhibiting very weak superlattice reflections. The Zn–Mg–Sc and Zn–Mg–Ti Quasicrystals have common features on diffraction intensity, stoichiometric composition, and average concentration of valence electrons.
