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Register a new userDiscussion on clusters, phasons, and quasicrystal stabilisation
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Added by
Christopher L. Henley
Publication date
2005
fields
Physics
and research's language is
English
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This paper summarises a two-hour discussion at the Ninth International Conference on Quasicrystals, including nearly 20 written comments sent afterwards, concerning (i) the meaning [if any] of clusters in quasicrystals; (ii) phason elasticity, and (iii) thermodynamic stabilisation of quasicrystals.
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An inelastic neutron scattering study of the lattice dynamics of the martensite phase of the ferromagnetic shape memory alloy, Ni2MnGa, reveals the presence of well-defined phasons associated with the charge density wave (CDW) resulting from Fermi surface (FS) nesting. The velocity and the temperature dependence of the phason are measured as well as the anomalous [110]-TA2 phonon.
Spin correlations and fluctuations in the 3d-transition-metal-based icosahedral quasicrystal Zn-Fe-Sc have been investigated by neutron scattering using polycrystalline samples. Magnetic diffuse scattering has been observed in the elastic experiment at low temperatures, indicating development of static short-range-spin correlations. In addition, the inelastic scattering experiment detects a $Q$-independent quasielastic signal ascribed to single-site relaxational spin fluctuations. Above the macroscopic freezing temperature $T_{rm f} simeq 7$ K, the spin relaxation rate shows Arrhenius-type behavior, indicating thermally activated relaxation process. In contrast, the relaxation rate remains finite even at the lowest temperature, suggesting a certain quantum origin for the spin fluctuations below $T_{rm f}$.
The tunability of the interlayer coupling by twisting one layer with respect to another layer of two-dimensional materials provides a unique way to manipulate the phonons and related properties. We refer to this engineering of phononic properties as Twistnonics. We study the effects of twisting on low-frequency shear (SM) and layer breathing (LBM) modes in transition metal dichalcogenide (TMD) bilayer using atomistic classical simulations. We show that these low-frequency modes are extremely sensitive to twist and can be used to infer the twist angle. We find unique ultra-soft phason modes (frequency $lesssim 1 mathrm{cm^{-1}}$, comparable to acoustic modes) for any non-zero twist, corresponding to an textit{effective} translation of the moir{e} lattice by relative displacement of the constituent layers in a non-trivial way. Unlike the acoustic modes, the velocity of the phason modes is quite sensitive to twist angle. As twist angle decreases, ($theta lesssim 3^{circ}, gtrsim 57^{circ}$) the ultra-soft modes represent the acoustic modes of the emergent soft moir{e} scale lattice. Also, new high-frequency SMs appear, identical to those in stable bilayer TMD ($theta = 0degree/60degree$), due to the overwhelming growth of stable stacking regions in relaxed twisted structures. Furthermore, we find remarkably different structural relaxation as $theta to 0^{circ}$, $to 60^{circ}$ due to sub-lattice symmetry breaking. Our study reveals the possibility of an intriguing $theta$ dependent superlubric to pinning behavior and of the existence of ultra-soft modes in textit{all} two-dimensional (2D) materials.
Kirigami, the art of introducing cuts in thin sheets to enable articulation and deployment, has till recently been the domain of artists. With the realization that these structures form a novel class of mechanical metamaterials, there is increasing interest in using periodic tiling patterns as the basis for the space of designs. Here, we show that aperiodic quasicrystals can also serve as the basis for designing deployable kirigami structures and analyze their geometrical, topological and mechanical properties. Our work explores the interplay between geometry, topology and mechanics for the design of aperiodic kirigami patterns, thereby enriching our understanding of the effectiveness of kirigami cuts in metamaterial design.
We report the discovery of a new binary icosahedral phase in a Sc-Zn alloy obtained through solution-growth, producing millimeter-sized, facetted, single grain, quasicrystals that exhibit different growth morphologies, pentagonal dodecahedra and rhombic triacontahedra, under only marginally different growth conditions. These two morphologies manifest different degrees of quasicrystalline order, or phason strain. The discovery of i-Sc$_12$Zn$_88$ suggests that a reexamination of binary phase diagrams at compositions close to crystalline approximant structures may reveal other, new binary quasicrystalline phases.
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