Lattice Modes Research Articles

Novel applications of local optimization semi-Cartesian grid for the complex band structure analysis of phononic crystals

In this paper, we propose a finite element method based on the Floquet transform and local optimization semi-Cartesian grid to compute the complex band structure of phononic crystals. Floquet transform is applied to transform the elastic wave equation into a quadratic eigenvalue equation. Value-periodic test function independent of the interface is defined to derive the weak formulation. The local optimization semi-Cartesian grid is proposed to improve the quality of triangular elements near the interface. Our results are in good agreement with ones obtained by other mature methods, and the purely propagative mode coincides with the traditional band diagram. In addition to simple scatterer shapes such as circle or square, the proposed method is able to calculate the complex band structures of phononic crystals with complicated scatterer shapes. Numerical experiments demonstrated the effectiveness of this method in the computation of anisotropic inhomogeneous medium. The complex band structures under different lattice types, scatterer shapes, material properties, rotation angle and modes are obtained, and their effects on the width and number of band gaps are analyzed.

Two-dimensional localized modes in saturable quintic nonlinear lattices

Two-dimensional localized modes in saturable quintic nonlinear lattices

Ca3SiO4Cl2—An Anthropogenic Phase from Burnt Mine Dumps of the Chelyabinsk Coal Basin: Crystal Structure Refinement, Spectroscopic Study and Thermal Evolution

The mineral-like phase Ca3SiO4Cl2, an anthropogenic anhydrous calcium chlorine-silicate from the Chelyabinsk coal basin has been investigated using single-crystal and high-temperature powder X-ray diffraction and Raman spectroscopy. The empirical formula of this phase was calculated as Ca2.96[(Si0.98P0.03)Σ1.01O4]Cl2, in good agreement with its ideal formula. Ca3SiO4Cl2 is monoclinic, space group P21/c, Z = 4, a = 9.8367(6) Å, b = 6.7159(4) Å, c = 10.8738(7) Å, β = 105.735(6)°, V = 691.43(8) Å3. The crystal structure is based upon the pseudo-layers formed by Ca–O and Si–O bonds separated by Cl atoms. The pseudo-layers are parallel to the (100) plane. The crystal structure of Ca3SiO4Cl2 was refined (R1 = 0.037) and stable up to 660 °C; it expands anisotropically with the direction of the strongest thermal expansion close to parallel to the [−101] direction, which can be explained by the combination of thermal expansion and shear deformations that involves the ‘gliding’ of the Ca silicate layers relative to each other. The Raman spectrum of the compound contains the following bands (cm–1): 950 (ν3), 848 (ν1), 600 (ν4), 466 (ν2), 372 (ν2). The bands near 100–200 cm−1 can be described as lattice modes. The compound had also been found under natural conditions in association with chlorellestadite.

Plasmonic Lattice Modes Formed Under Both Forward and Backward Illuminations in Inhomogeneous Environment

Plasmonic Lattice Modes Formed Under Both Forward and Backward Illuminations in Inhomogeneous Environment

Subtle lattice distortion-driven phase transitions in layered ACu4As2 (A = Eu, Sr)

The compounds composed of transition metal cations and pnictide anions provide a rich platform for studying novel physical phenomena. Here we report on the observation of a phase transition at ∼ 70 K and 145 K in layered compound EuCu4As2 and SrCu4As2, respectively. from both the transport and heat capacity. The thermal expansion measurements show that the variation of the lattice parameters (ΔLb /Lab ) around T P is much less than that for a typical crystalline phase transition. Our experimental results reveal that the transition in EuCu4As2 and SrCu4As2 should be driven by subtle structural-distortion.

Lattice instability and magnetic phase transitions in strongly correlated MnAs

Using variable temperature x-ray total scattering in magnetic field, we study the interaction between lattice and magnetic degrees of freedom in MnAs, which loses its ferromagnetic order and hexagonal (‘H’) lattice symmetry at 318 K to recover the latter and become a true paramagnet when the temperature is increased to 400 K. Our results show that the 318 K transition is accompanied by highly anisotropic displacements of Mn atoms that appear as a lattice degree of freedom bridging the ‘H’ and orthorhombic phases of MnAs. This is a rare example of a lowering of an average crystal symmetry due to an increased displacive disorder emerging on heating. Our results also show that magnetic and lattice degrees of freedom appear coupled but not necessarily equivalent control variables for triggering phase transitions in strongly correlated systems in general and in particular in MnAs.

Molecular-Induced Chirality Transfer to Plasmonic Lattice Modes.

Molecular chirality plays fundamental roles in biology. The chiral response of a molecule occurs at a specific spectral position, determined by its molecular structure. This fingerprint can be transferred to other spectral regions via the interaction with localized surface plasmon resonances of gold nanoparticles. Here, we demonstrate that molecular chirality transfer occurs also for plasmonic lattice modes, providing a very effective and tunable means to control chirality. We use colloidal self-assembly to fabricate non-close packed, periodic arrays of achiral gold nanoparticles, which are embedded in a polymer film containing chiral molecules. In the presence of the chiral molecules, the surface lattice resonances (SLRs) become optically active, i.e., showing handedness-dependent excitation. Numerical simulations with varying lattice parameters show circular dichroism peaks shifting along with the spectral positions of the lattice modes, corroborating the chirality transfer to these collective modes. A semi-analytical model based on the coupling of single-molecular and plasmonic resonances rationalizes this chirality transfer.

Microwave dielectric properties of ternary molybdate NaSrLn(MoO4)3 (Ln = Nd, Sm) ceramics for LTCC applications

Two kinds of scheelite-structure microwave dielectric ceramics with I41/a space group were prepared by the conventional solid-phase reaction method. The effects of different sintering temperatures on the crystal structure, lattice vibration and microwave dielectric properties of NaSrLn(MoO4)3 (Ln = Nd, Sm) ceramics were investigated. XRD and Rietveld refinement results show that NaSrLn(MoO4)3 (Ln = Nd, Sm) ceramics belong to tetragonal scheelite structure with I41/a space group. The lattice vibration mode was analyzed by Raman spectroscopy, and the correlation between the dielectric performances and structure was established. The NaSrLn(MoO4)3 (Ln = Nd, Sm) ceramics have high density (>97%) and excellent microwave dielectric properties of εr = 10.47, Qf = 38951 GHz, τf = −48.43 ppm/°C for NaSrNd(MoO4)3 sintered at 775 °C and εr = 9.55, Qf = 41081 GHz, τf = −44.92 ppm/°C for NaSrSm(MoO4)3 sintered at 800 °C. In addition, NaSrLn(MoO4)3 (Ln = Nd, Sm) ceramics have excellent chemical compatibility with Ag electrodes, which means that the ceramic could be used in LTCC microwave devices.

Phase transitions of L-histidinium hydrogen oxalate crystal under high pressures investigated by Raman spectroscopy

L-histidinium hydrogen oxalate (L-HisH)(HC2O4) crystal is formed from amino acid. L-histidine with oxalic acid whose vibrational high pressures behavior have not yet been investigated in the literature. Here we synthesized (L-HisH)(HC2O4) crystal by slow solvent evaporation method in a 1:1 ratio of L-histidine and oxalic acid. In addition, a vibrational study of (L-HisH)(HC2O4) crystal as a function of pressure was performed via Raman spectroscopy in the pressure range of 0.0–7.3 GPa. From analysis of the behavior of the bands within 1.5–2.8 GPa, characterized by the disappearance of lattice modes, the occurrence of a conformational phase transition was noted. A second phase transition, now from structural type, close to 5.1 GPa was observed due to the incidence of considerable changes in lattice and internal modes, mainly in vibrational modes related to imidazole ring motions.

Design and fabrication of 3D-printed composite metastructure with subwavelength and ultrawide bandgaps

Architected composite metastructures can exhibit a subwavelength ultrawide bandgap (BG) with prominent emerging applications in the structural vibration and noise control and, elastic wave manipulation. The present study implemented both forward and inverse design methods based on numerical simulations and machine learning (ML) methods, respectively to design and fabricate an architected composite metastructure exhibiting subwavelength and ultrawide BGs. The multilayer perceptron and radial basis function neural networks are developed for the inverse design of the composite metastructure and their accuracy and computation time are compared. The band structure revealed the presence of subwavelength and ultrawide BGs generated through local resonance and structural modes of the periodic composite lattice. Both in-plane and out-of-plane local resonant modes of the periodic lattice structure were responsible for inducing the BGs. The findings are confirmed by calculating numerical wave transmission curves and experiment tests on the fabricated supercell structures, utilizing 3D-printing technology. Both numerical and experimental results validate the ML prediction and the presence of subwavelength and ultrawide BG was observed. The design approach, research methodology and proposed composite metastructure will have a wide range of application in the structural vibration control and shock absorption.

Dynamical phase transitions in dimerized lattices

Nonequilibrium evolution of the quantum states extend the notion of quantum phase transition to a dynamical scenario, corresponding to the singular behavior of Loschmidt echo in quenched systems. In this work, we uncover the signature of dynamical phase transition in a quenched Aubry–André model with dimerized hoppings. By investigating the Loschmidt echo, we find a dynamical phase transition originating from the interplay between dimerized hopping and the strength of incommensurate potential. The dimerized hoppings may cause a dynamical phase transition in the process of the quench dynamics between the prequenched and postquenched system Hamiltonians.

Ferroelectric phase transition driven by anharmonic lattice mode coupling in two-dimensional monolayer In2Se3

In this paper, to better understand the physical origin of spontaneous out-of-plane (OOP) polarization in the wildly investigated two-dimensional (2D) material monolayer (ML) ${\mathrm{In}}_{2}{\mathrm{Se}}_{3}$, we studied its lattice dynamics behaviors via performing a series of first-principles calculations. Cooperating with a fitted phenomenological model, it is clearly shown that, although the depolarization field is nonzero, spontaneous OOP polarization will survive through the anharmonic coupling with other lattices modes. Additionally, our results indicated that the conventional proper ferroelectric (FE) transition of in-plane (IP) polarization plays a role in the primary driving force for the transition in lattice. Tuning the stability of the IP polar modes can be considered an effective pathway of controlling the FE behavior in ML ${\mathrm{In}}_{2}{\mathrm{Se}}_{3}$ and related III-VI group 2D materials.

Investigation on the Compressive Behavior of Hybrid Polyurethane(PU)-Foam-Filled Hyperbolic Chiral Lattice Metamaterial.

In this study, a novel hybrid metamaterial has been developed via fulfilling hyperbolic chiral lattice with polyurethane (PU) foam. Initially, both the hyperbolic and typical body-centered cubic (BCC) lattices are fabricated by 3D printing technique. These lattices are infiltrated in a thermoplastic polyurethane (TPU) solution dissolved in 1,4-Dioxane, and then freeze casting technique is applied to achieve the PU-foam-filling. Intermediate (IM) layers possessing irregular pores, are formed neighboring to the lattice-foam interface. While, the foam far from the lattice exhibits a multi-layered structure. The mechanical behavior of the hybrid lattice metamaterials has been investigated by monotonic and cyclic compressive tests. The experimental monotonic tests indicate that, the filling foam is able to soften the BCC lattice but to stiffen the hyperbolic one, further to raise the stress plateau and to accelerate the densification for both lattices. The foam hybridization also benefits the hyperbolic lattice to prohibit the property degradation under the cyclic compression. Furthermore, the failure modes of the hybrid hyperbolic lattice are identified as the interface splitting and foam collapse via microscopic analysis. Finally, a parametric study has been performed to reveal the effects of different parameters on the compressive properties of the hybrid hyperbolic lattice metamaterial.

Anti-holomorphic modes in vortex lattices

A continuum theory of linearized Helmholtz-Kirchoff point vortex dynamics about a steadily rotating lattice state is developed by two separate methods: firstly by a direct procedure, secondly by taking the long-wavelength limit of Tkachenko’s exact solution for a triangular vortex lattice. Solutions to the continuum theory are found, described by arbitrary anti-holomorphic functions, and give power-law localized edge modes. Numerical results for finite lattices show excellent agreement to the theory.

Hybridization of surface lattice modes: towards plasmonic metasurfaces with high flexible tunability

Abstract When assembled in periodic arrangements, metallic nanostructures (NSs) support plasmonic surface lattice (SL) resonances resulting from long-range interactions these surface lattice resonances differ radically from localized surface plasmon (LSP). Similarly to the hybridization of LSP resonances, observed in short-range interactions, we demonstrate the possibility to generate a hybridization of surface lattice (SL) plasmon resonances, by the excitation of grazing order diffraction within the metasurface. This hybridization leads to the emergence of bonding and anti-bonding modes. If hybridization of LSP modes has been widely described in recent literature, there is still no experimental proof-of-concept reporting such hybridization with SL plasmon resonances. We fill this gap in the present paper by considering surfaces made of binary arrays with unit cells made of two gold disks of distinct diameters. We demonstrate the possibility to maximize or cancel the interaction between the hybridized SL resonances by simply controlling the distance between particles. All our experimental results are supported by FDTD calculations. The hybridization of SL modes results in much richer hybridization scenario in terms of wavelength and quality factor control, compared to a hybridization of LSP in a short-range configuration. It offers unprecedented opportunities to generate innovative optical devices, with high flexible tunability.

Thermal transport properties and lattice vibration modes in crystalline and amorphous LaMgAl11O19

Thermal energy transport plays a crucial role in determining the performance of LaMgAl11O19-based applications. Herein, we report the inherent thermal transport in crystalline (c-LMA) and amorphous LMA (a-LMA) using atomistic simulations. It is found that c-LMA have a low κ comparable to the classical 7YSZ at 300–1500 K, while the κ of a-LMA is 8–68% lower than that of c-LMA. The mode decomposition shows that the phonon modes in c-LMA consist of local, normal and diffuse modes, while those in a-LMA consist of local and diffuse modes. The dual-channel model reveals that the thermal conduction in c-LMA is dominated by the normal modes at low temperatures (<420 K) while by the diffusive modes at high temperatures, but that in a-LMA results entirely from diffusive modes. This new insight into the thermal transport properties in c-LMA and a-LMA provides a foundation for designing LH-based thermal management applications.

Interaction of plasmonic bound states in the continuum

Bound states in continuum (BICs) are believed to have the ability to achieve high quality factor (Q factor) resonances, which is very important for plasmonics. However, the study of plasmonic BICs is not sufficient. Herein, we design and fabricate a metal−insulator−metal (MIM) metasurface and demonstrate a one-dimensional plasmonic BIC experimentally. The even-order localized surface plasmon resonance (LSPR) modes have even parity at normal incidence. The symmetry-protected BIC can be achieved at Γ point. The band structure can be tuned by strong coupling between the localized plasmonic resonance and plasmonic lattice mode. Interestingly, two of the hybrid modes are also BICs. Although BICs cannot interact with the far field, we successfully demonstrate BIC splitting through far-field excitation. By further tuning the pitch of the MIM grating, the Friedrich–Wintgen BIC is also observed. Finally, we propose and preliminarily demonstrate an ultrathin bandpass spatial filter. These findings provide a new platform to study optical multipole BICs and can have applications in fields such as nano lasers, ultrasensitive sensors, filters, nonlinearity enhancement, and quantum optics.

Ultrasensitive Refractive Index Sensing Based on Hybrid High-Q Metasurfaces

High sensitivity and a large quality factor (Q) are two desirable goals to achieve a high figure of merit (FoM) in refractive index (RI) sensing. However, simultaneously satisfying these two goals is challenging. Herein, we propose a new class of hybrid high-Q metasurfaces, which are dielectric arrays standing on a Au plasmonic nanofilm, possessing the advantages of both high RI sensitivity and a large Q. The hybrid metasurface can support the plasmon-coupled lattice mode, which has extremely narrow full width at half-maximum (fwhm) resulting in a high-Q. The hybrid metasurface can be fabricated by a facile straightforward lithography technique and exhibits ultrahigh FoM values over a wide RI range (1–1.384) due to its narrow fwhm (smaller than 1 nm) and tunable high RI sensitivity. The highest Q and FoM values of 2370 and 1431 were experimentally demonstrated, respectively, giving the proposed hybrid metasurface great potential for building advanced optical biosensors in future applications.

Microstructure Formation and Mechanical Properties of Metastable Titanium-Based Gradient Coating Fabricated via Intense Pulse Ion Beam Melt Mixing.

The unique flash heating characteristics of intense pulsed ion beams (IPIB) offer potential advantages to fabricate high-performance coatings with non-equilibrium structures. In this study, titanium-chromium (Ti-Cr) alloy coatings are prepared through magnetron sputtering and successive IPIB irradiation, and the feasibility of IPIB melt mixing (IPIBMM) for a film-substrate system is verified via finite elements analysis. The experimental results reveal that the melting depth is 1.15 μm under IPIB irradiation, which is in close agreement with the calculation value (1.18 μm). The film and substrate form a Ti-Cr alloy coating by IPIBMM. The coating has a continuous gradient composition distribution, metallurgically bonding on the Ti substrate via IPIBMM. Increasing the IPIB pulse number leads to more complete element mixing and the elimination of surface cracks and craters. Additionally, the IPIB irradiation induces the formation of supersaturated solid solutions, lattice transition, and preferred orientation change, contributing to an increase in hardness and a decrease in elastic modulus with continuous irradiation. Notably, the coating treated with 20 pulses demonstrates a remarkable hardness (4.8 GPa), more than twice that of pure Ti, and a lower elastic modulus (100.3 GPa), 20% less than that of pure Ti. The analysis of the load-displacement curves and H-E ratios indicates that the Ti-Cr alloy coated samples exhibit better plasticity and wear resistance compared to pure Ti. Specifically, the coating formed after 20 pulses exhibits exceptional wear resistance, as demonstrated by its H3/E2 value being 14 times higher than that of pure Ti. This development provides an efficient and eco-friendly method for designing robust-adhesion coatings with specific structures, which can be extended to various bi- or multi-element material systems.

Magnetotransport‐Induced Non‐Contact Terahertz Detection of Weak Magnetic Fields in Optically Thin Frequency‐Agile Superlattice Metasurfaces

AbstractMagnetotransport, the magnetic field induced electron transport phenomenon through metals and semiconductors, has proven to be a useful technique to tailor the properties of electromagnetic radiation upon interaction with suitable materials and structures. Very recently, magnetotransport has become an important tool to dynamically tailor terahertz (THz) radiation and response of different optical devices. Based on these backgrounds, optically thin, subwavelength superlattice (with alternate arrangement of four metallic films: two non‐magnetic aluminum [Al] and two ferromagnetic nickel [Ni] films, having thickness of each film as 10 nm) metasurfaces are demonstrated, consisting of periodic arrays of asymmetric cut‐wire pair metasurfaces, which have a unique ability to exhibit both frequency and intensity modulation at its hybridized resonances when low‐intensity magnetic fields are applied. Such dynamic tuning characteristics are attributed to the combined effects of spin‐dependent THz magnetotransport in superlattice films, near‐field electromagnetic coupling between the resonators, and lattice mode coupling. Such THz metasurface is further employed for non‐contact detection of external magnetic fields in the range of 0–30 mT, while operating at the optically thin regime. The demonstrated scheme can further be extended to realize THz magneto‐spectroscopy toward devising state‐of‐the‐art photonic and magnetic technologies.