Lattice Form Research Articles

Unconventional Flat Chern Bands and 2e Charges in Skyrmionic Moiré Superlattices

The interplay of topological characteristics in real space and reciprocal space can lead to the emergence of unconventional topological phases. In this Letter, we implement a novel mechanism for generating higher-Chern flat bands on the basis of twisted bilayer graphene (TBG) coupled to topological magnetic structures in the form of the skyrmion lattice. In particular, we discover a scenario for generating |C| = 2 dispersionless electronic bands when the skyrmion periodicity and the moiré periodicity match. Following the Wilczek argument, the statistics of the charge-carrying excitations in this case is bosonic, characterized by electronic charge Q = 2e, which is even in units of electron charge e. The skyrmion coupling strength triggering the topological phase transition is realistic, with its lower bound estimated as 4 meV. The Hofstadter butterfly spectrum results in an unexpected quantum Hall conductance sequence for TBG with the skyrmion order.

Tunning the tilt of the Dirac cone by atomic manipulations in 8Pmmn borophene

Two dimensional quantum materials possessing Dirac cones in their spectrum are fascinating due to their emergent low-energy Dirac fermions. In 8Pmmn borophene the Dirac cone is furthermore tilted, which is a proxy for spacetime geometry, since the future light-cone depends on the underlying metric. Therefore it is important to understand the microscopic origin of the tilt. Here, based on ab-initio calculations, we decipher the atomistic mechanism of the formation of tilt. First, nearest-neighbor hopping on a buckled honeycomb lattice forms an upright Dirac cone. Then, the difference in the renormalized anisotropic second-neighbor hopping, formed by virtual hoppings on one-dimensional chains of atoms, tilts the Dirac cone. We construct an accurate tight-binding model on honeycomb graph for analytical investigation, and we find that substitution of certain boron atoms by carbon provides a way to change the tilt of the cone.

Refraction, beam splitting and dispersion of GHz surface acoustic waves by a phononic crystal

We exploit a time-resolved ultrafast optical technique to study the propagation of point-excited surface acoustic waves on a microscopic two-dimensional phononic crystal in the form of a square lattice of holes in a silicon substrate. Constant-frequency images and the dispersion relation are extracted, and the latter measured in detail in the region around the phononic band gap. Mode conversion and refraction at the interface between the phononic crystal and surrounding non-structured silicon substrate is studied at constant frequencies. Symmetric phonon beam splitting, for example, is shown to lead to a striking Maltese-cross pattern when phonons exit a square region of phononic crystal excited near its center.

Supersymmetric non-Hermitian topological interface laser

We investigate laser emission at the interface of a topological and trivial phases with loss and gain. The system is described by a Su-Schrieffer-Heeger model with site-dependent hopping parameters. We study numerically and analytically the interface states. The ground state is described by the Jackiw-Rebbi mode with a pure imaginary energy, reflecting the non-Hermiticity of the system. It is strictly localized only at the A sites. We also find a series of analytic solutions of excited states based on SUSY quantum mechanics, where the A and B sites of the bipartite lattice form SUSY partners. We then study the system containing loss and gain with saturation. The Jackiw-Rebbi mode is extended to a nonlinear theory, where B sites are also excited. The relative phases between A and B sites are fixed, and hence it will serve as a large area coherent laser.

High Thermoelectric Performance in Earth‐Abundant Cu3SbS4 by Promoting Doping Efficiency via Rational Vacancy Design

AbstractSulfides are well investigated as thermoelectric materials but their performance is typically limited by low electrical conductivity. High electrical performance in Cu3SbS4 is reported by creating high valence vacancies, which efficiently provides multiple carriers. It is revealed from the perspective of a chemical bond by calculations that Al can serve as vacancy stabilizer as its entry into the lattice forms intensified bonds with neighboring atoms and lowers the vacancy formation energy. As a result, the average power factor of Cu3SbS4 with 9 wt% CuAlS2 reaches 16.1 µW cm−1 K−2. Finally, by further addition of AgAlS2, a peak zT of 1.3 and an average zT of 0.77 are obtained due to the reduced thermal conductivity. The attained average power factor and average zT are superior to other low‐toxic thermoelectric sulfides. The findings shed light on the new strategy for creating favorable vacancies to realize high‐efficiency doping in thermoelectric materials.

An ab initio approach to anisotropic alloying into the Si(001) surface.

By employing density functional theory calculations, we explore the initial stage of competitive alloying of co-deposited silver and indium atoms into a silicon surface. In particular, we identify respective adsorption positions and activation barriers governing their diffusion on a dimer-reconstructed silicon surface. Furthermore, we develop a growth model that appropriately describes diffusion mechanisms and silicon morphology with the account of silicon dimerization and the presence of C-type defects. Based on the surface kinetic Monte Carlo simulations, we examine the dynamics of bimetallic adsorption and elaborate on the temperature effects on the submonolayer growth of an Ag-In alloy. A close inspection of adatom migration clearly indicates effective nucleation of Ag and In atoms, followed by the formation of orthogonal atomic chains. We show that the epitaxial bimetallic growth might potentially lead to exotic ordering of adatoms in the form of anisotropic two-dimensional lattices via orthogonally oriented single-metal rows. We argue that this scenario becomes favorable provided above room temperature, while our numerical results are shown to be in agreement with the experimental findings.

ЧУТЛИВИЙ ЕЛЕМЕНТ СЕНСОРА ПОВЕРХНЕВИХ ПЛАЗМОНІВ З ТЕРМІЧНОЮ МОДИФІКАЦІЄЮ СТРУКТУРНИХ ВЛАСТИВОСТЕЙ ПОЛІМЕРНОЇ ПІДКЛАДКИ

The development of an effective sensing element (ChE) sensor with a prism type of excitation (Kretchman configuration) of surface plasmon resonance (SPR) in a gold film and a mechanical survey of the angle of incidence of monochromatic light based on a polymer substrate is based on a combination of radiation binding schemes using a prism and a lattice to prevent losses in the active metal film. Replacing the glass substrate with a polymer one has reduced the cost of ChE, led to increased sensitivity and simplification of its manufacturing technology, which does not require the use of intermediate adhesion layers. Additionally, we applied a thermal method of modifying the optical and structural properties of the substrate – hot pressing of the matrix, which contained a periodically nanostructured surface relief in the form of a diffraction two-dimensional (2D) lattice. The original 2D lattice was recorded on photoresist-covered (Shepley 1805) glass plates using the method of two-beam interference (He-Cd laser, = 440 nm) at double exposure (time 2040 s, power 20 mW/cm2) of the sample with a rotation of 90. Characteristics of ChE on an optical polycarbonate substrate (d = 2.25 mm, n = 1.58 at ( = 650 nm) after hot pressing, which contained a flat and periodically nanostructured surface in the form of a diffraction 2D lattice, followed by the deposition of a thin (d 40 nm) layer of gold on them was examined using an atomic force microscope (AFM) and the device "Plasmon". AFM studies have shown that the technological technique used made it possible to obtain lateral-ordered structures in the form of pyramids with calculated parameters – a period of 422435 nm (spatial frequency of about 2350 lin/mm) and a relief depth of 7090 nm. However, the preservation of a wave-like relief (about 300 nm) on a flat part of the surface and double ray refraction of the polymer substrate, encourage optimization of the hot pressing process using the resulting matrix on polymer substrates of smaller thickness.

Engineering quantum states and electronic landscapes through surface molecular nanoarchitectures

Surfaces are at the frontier of every known solid. They provide versatile supports for functional nanostructures and mediate essential physicochemical processes. Being intimately related with 2D materials, interfaces and atomically thin films often feature distinct electronic states with respect to the bulk, which are key for many relevant properties, such as catalytic activity, interfacial charge-transfer, or crystal growth mechanisms. Of particular interest is reducing the surface electrons' dimensionality and spread with atomic precision, to induce novel quantum properties via lateral scattering and confinement. Both atomic manipulation and supramolecular principles provide access to custom-designed molecular superlattices, which tailor the surface electronic landscape and influence fundamental chemical and physical properties at the nanoscale. Herein, we review the confinement of surface state electrons focusing on their interaction with molecule-based scaffolds created by molecular manipulation and self-assembly protocols under ultrahigh vacuum conditions. Starting from the quasi-free 2D electron gas present at the (111)-terminated surface planes of noble metals, we illustrate the enhanced molecule-based structural complexity and versatility compared to simple atoms. We survey low-dimensional confining structures in the form of artificial lattices, molecular nanogratings or quantum dot arrays, which are constructed upon appropriate choice of their building constituents. Whenever the realized (metal-)organic networks exhibit long-range order, modified surface band structures with characteristic features emerge, revealing intriguing physical properties, such as discretization, quantum coupling or energy and effective mass renormalization. Such collective electronic states can be additionally modified by positioning guest species at the voids of open nanoarchitectures [...].

Novel Ni3S4/NiS/NC composite with multiple heterojunctions synthesized through space-confined effect for high-performance supercapacitors

The construction of heterojunctions in composite materials to optimize the electronic structures and active sites of energy materials is considered to be the promising strategy for the fabrication of high-performance electrochemical energy devices. In this paper, a one-step, easy processing and cost-effective technique for generating composite materials with heterojunctions was successfully developed. The composite containing Ni3S4, NiS, and N-doped amorphous carbon (abbreviated as Ni3S4/NiS/NC) with multiple heterojunction nanosheets are synthesized via the space-confined effect of molten salt interface of recrystallized NaCl. Several lattice matching forms of Ni3S4 with cubic structure and NiS with hexagonal structure are confirmed by the detailed characterization of heterogeneous interfaces. The C–S bonds are the key factor in realizing the chemical coupling between nickel sulfide and NC and constructing the stable heterojunction. Density functional theory calculations further revealed that the electronic interaction on the heterogeneous interface of Ni3S4/NiS can contribute to high electronic conductivity. The heterogeneous interfaces are identified to be the good electroactive region with excellent electrochemical performance. The synergistic effect of abundant active sites, the enhanced kinetic process and valid interface charge transfer channels of Ni3S4/NiS/NC multiple heterojunction can guarantee high reversible redox activity and high structural stability, resulting in both high specific capacitance and energy/power densities when it is used as the electrode for supercapacitors. This work offers a new avenue for the rational design of the heterojunction materials with improved electrochemical performance through space-confined effect of NaCl.

Surfactant-Modified CdS/CdCO3 Composite Photocatalyst Morphology Enhances Visible-Light-Driven Cr(VI) Reduction Performance.

The surfactant modification of catalyst morphology is considered as an effective method to improve photocatalytic performance. In this work, the visible-light-driven composite photocatalyst was obtained by growing CdS nanoparticles in the cubic crystal structure of CdCO3, which, after surfactant modification, led to the formation of CdCO3 elliptical spheres. This reasonable composite-structure-modification design effectively increased the specific surface area, fully exposing the catalytic-activity check point. Cd2+ from CdCO3 can enter the CdS crystal structure to generate lattice distortion and form hole traps, which productively promoted the separation and transfer of CdS photogenerated electron-hole pairs. The prepared 5-CdS/CdCO3@SDS exhibited excellent Cr(VI) photocatalytic activity with a reduction efficiency of 86.9% within 30 min, and the reduction rate was 0.0675 min-1, which was 15.57 and 14.46 times that of CdS and CdCO3, respectively. Finally, the main active substances during the reduction process, the photogenerated charge transfer pathways related to heterojunctions and the catalytic mechanism were proposed and analyzed.

Spatial‐temporal modulation in radiation therapy

Spatial‐temporal modulation in radiation therapy

Vortex patterns in rapidly rotating Rayleigh–Bénard convection under spatial periodic forcing

Pattern-forming with externally imposed symmetry is ubiquitous in nature but little studied. We present experimental studies of pattern formation and selection by spatial periodic forcing in rapidly rotating convection. When periodic topographic structures are constructed on the heated boundary, they modulate the local temperature and velocity fields. Symmetric convection patterns in the form of regular vortex lattices are observed near the onset of convection, when the periodicity of the external forcing is set close to the intrinsic vortex spacing. We show that the new patterns arise as a dynamical process of imperfect bifurcation which is well described by a Ginzburg–Landau-like model. We explore the phase diagram of buoyancy strength and periodicity of external forcing to find the optimal experimental settings for which the vortex patterns best match that of the external forcing.

Compressive properties of cementitious composites reinforced by 3D printed PA 6 lattice

The lattice-reinforced cementitious composites prepared by placing 3D printed lattices in cementitious matrix has been proved to be effective in improving the bending mechanical properties of cement-based materials, such as improving ductility and brittleness. However, the compressive properties of 3D printed lattice-reinforced cementitious composites are still an open question. In this paper, the compressive properties of 3D printed polyamide 6 (PA6) lattice-reinforced cementitious composites with different structural forms were studies. Six kinds of lattices were fabricated by multi jet fusion (MJF) technique. The volumes of these lattices are identical to ensure that the volume enhancement ratio of the lattices in the cementitious composite specimen is the same. The plain cementitious matrix without lattice was set as the control group, and two nondestructive testing methods, AE and DIC, were used to compare the compressive properties between plain cementitious matrix and lattice-reinforced cementitious composites with different structural forms. The experimental results show that the 3D printed lattice can significantly improve the mechanical properties and failure modes of cement-based materials under uniaxial compression. In contrast, the six lattice forms used in this study can improve the maximum compressive bearing capacity and deformation capacity of the cement-based materials under uniaxial compression test, and reduce the damage of cement-based materials in the elastic deformation stage. This paper confirms that 3D printed lattices can improve the compressive properties of cement-based materials and provide a new method for improving the compressive strength of cement-based materials. At the same time, it provides new ideas for the development of ideal substitutes for steel bars in corrosive environments, energy conservation and emission reduction and the development of green buildings.

New physics effects on Λb→Λc*τν¯τ decays

We benefit from a recent lattice determination of the full set of vector, axial and tensor form factors for the ${\mathrm{\ensuremath{\Lambda}}}_{b}\ensuremath{\rightarrow}{\mathrm{\ensuremath{\Lambda}}}_{c}^{*}(2595)\ensuremath{\tau}{\overline{\ensuremath{\nu}}}_{\ensuremath{\tau}}$ and ${\mathrm{\ensuremath{\Lambda}}}_{c}^{*}(2625)\ensuremath{\tau}{\overline{\ensuremath{\nu}}}_{\ensuremath{\tau}}$ semileptonic decays to study the possible role of these two reactions in lepton flavor universality violation studies. Using an effective theory approach, we analyze different observables that can be accessed through the visible kinematics of the charged particles produced in the tau decay, for which we consider the ${\ensuremath{\pi}}^{\ensuremath{-}}{\ensuremath{\nu}}_{\ensuremath{\tau}},{\ensuremath{\rho}}^{\ensuremath{-}}{\ensuremath{\nu}}_{\ensuremath{\tau}}$ and ${\ensuremath{\mu}}^{\ensuremath{-}}{\overline{\ensuremath{\nu}}}_{\ensuremath{\mu}}{\ensuremath{\nu}}_{\ensuremath{\tau}}$ channels. We compare the results obtained in the Standard Model and other schemes containing new physics (NP) interactions, with either left-handed or right-handed neutrino operators. We find a discriminating power between models similar to the one of the ${\mathrm{\ensuremath{\Lambda}}}_{b}\ensuremath{\rightarrow}{\mathrm{\ensuremath{\Lambda}}}_{c}$ decay, although somewhat hindered in this case by the larger errors of the ${\mathrm{\ensuremath{\Lambda}}}_{b}\ensuremath{\rightarrow}{\mathrm{\ensuremath{\Lambda}}}_{c}^{*}$ lattice form factors. Notwithstanding this, the analysis of these reactions is already able to discriminate between some of the NP scenarios and its potentiality will certainly improve when more precise form factors are available.

An analytical approach of nonlinear buckling behavior of torsionally loaded auxetic core toroidal shell segments with graphene reinforced polymer coatings

The buckling and nonlinear postbuckling analysis of toroidal shell segments with auxetic-core layer and Graphene-reinforced polymer coatings under torsional loads is reported in the present research. The functionally graded Graphene-reinforced polymer coatings are considered with three distribution laws, and the auxetic cores are designed in the honeycomb lattice forms. An auxetic homogenization technique is applied to establish the stiffness terms of the auxetic core. The combination of nonlinear von Karman Donnell shell theory and the Stain and McElman approximate is applied to formulate the nonlinear equilibrium equations of shells with the shallow longitudinal curvature considering the two-parameter foundation model. The deflection of shells is assumed to be a three-term form corresponding to the pre-buckling, linear and nonlinear postbuckling behaviors, and the Galerkin method is employed for three terms of defection. The torsion-deflection and torsion-twist angle postbuckling behaviors can be obtained in explicit forms. The numerical examinations validate the large effects of honeycomb lattice auxetic core, the functionally graded Graphene-reinforced polymer coatings, the parameters of shell’s geometric and foundation on the nonlinear buckling behaviors of shells.

A class of periodic lattices for tuning elastic instabilities

With in mind microstructures exhibiting unconventional macroscopic mechanical behaviors, characterized by overall auxetic responses and strain localization due to local elastic instabilities, in this work we conceived a simple two-dimensional non-chiral architecture in the form of a periodic lattice, whose drawing is decided by varying the thickness ratios of the cells’ walls and in turn their slenderness. Inspired by nature, which often uses supposedly naive geometries that conceal complex functions, and focusing the attention on two limit geometrical configurations of main interest, we show how these non-chiral settings, as a function of the prescribed boundary conditions, might lead to symmetry breaking associated to a variety of non-trivial deformation modes, which in some cases also retrace and generalize chiral as well as auxetic responses already observed in literature in simpler microstructures. Interestingly, for both the above mentioned limit cases, we were able to idealize the mechanical response of the system through geometrically nonlinear beam-based models, in this way obtaining helpful analytical solutions and explicit formulas to estimate the tangent effective stiffness of the lattice as well as the critical load at the onset of instability. The post-buckling was instead analyzed and discussed in detail through parametric numerical finite element simulations and ad hoc laboratory experiments, performed by faithfully realizing 3D printed prototypes, constructed via additive manufacturing technologies and made of rubber-like material, to follow extreme deformation patterns, including multi-stable states, localization and compaction with possible self-contact/touching of the elements. At the end, we exploited the obtained closed-form solutions and some associated inequalities to derive the transition from the discrete lattice to its continuum limit, which – together with the multiple equilibrium bifurcation points exhibited by the proposed microstructure – could be used to broaden the spectrum of metamaterial geometries designed to exhibit complex tunable properties.

Anisotropic magnon damping by zero-temperature quantum fluctuations in ferromagnetic CrGeTe3

Spin and lattice are two fundamental degrees of freedom in a solid, and their fluctuations about the equilibrium values in a magnetic ordered crystalline lattice form quasiparticles termed magnons (spin waves) and phonons (lattice waves), respectively. In most materials with strong spin-lattice coupling (SLC), the interaction of spin and lattice induces energy gaps in the spin wave dispersion at the nominal intersections of magnon and phonon modes. Here we use neutron scattering to show that in the two-dimensional (2D) van der Waals honeycomb lattice ferromagnetic CrGeTe3, spin waves propagating within the 2D plane exhibit an anomalous dispersion, damping, and breakdown of quasiparticle conservation, while magnons along the c axis behave as expected for a local moment ferromagnet. These results indicate the presence of dynamical SLC arising from the zero-temperature quantum fluctuations in CrGeTe3, suggesting that the observed in-plane spin waves are mixed spin and lattice quasiparticles fundamentally different from pure magnons and phonons.

Change the state of 2D nanofilms under the substrate influence

2D films deformations under action of ferroelectric substrate by computer modeling method are performed in article. The film has a square lattice. We use harmonic law for the energy of interatomic interaction. The substrate effect on the film is simulated by the 2D Frenkel-Kontorova potential. The orientation of the film and the substrate do not match. Different cases for periods of film and substrate are considered. The Monte Carlo method is used for computer modeling. If the period of the film and the substrate coincide, the film atoms are placed at the minimum points of the substrate. The film on the substrate has a square crystal lattice. If the period of the substrate is less than the period of the film, the continuous film is converted into a film 2D nanoparticles. The substrate potential amplitude affects the filling of the space between particles. If the period of the substrate is longer than the period of the film, a superstructure in the form of a periodic lattice with an increased particle concentration is formed in the film. The distribution of atoms in the superstructure is determined by the substrate potential amplitude of the substrate potential.

Key features of a swarm assemlby algorythm for autonomous unmanned aerial vehicles (UAVs) in absence of GNSS and stable radio communication

In this paper we describe application of the method of physical processes simulating to build a swarm of drones. We show that this method provides the construction of a swarm of drones in the form of a crystal lattice with specified parameters. We found those additional conditions that make it possible to assemble a swarm of disparate drones. We have proposed an algorithm that allows assembling a swarm with minimal costs using a simple measuring complex. Key words UAV, self-organization, physical processes simulating, crystal lattice, swarm robotics, sensors for UAV.

Use of two relative depths of the soil apparent electrical conductivity to define experimental blocks with spatial regression models

Aim of study: Our main objective was to take advantage of the ECa information that the EM38-MK2 sensor records simultaneously at two relative depths for modeling using spatial regression and the subsequent blocking of the conductivity estimate values, incorporating elevation. Area of study: A 23.1-ha field located in the municipality of Puerto López (Meta, Colombia). Material and methods: A series of georeferenced data (15438) was collected from the EM38-MK2 sensor, through which the ECa was obtained at two depths, a spatial aggregation was performed using a grid of 40 m ´ 40 m (167 grid cells), to provide data in Lattice form, the centroid of the cells was determined as the new representative spatial coordinates, to adjust a Spatial Autoregression Model (SAC), and then define the blocks from the predictions of the adjusted model. Main results: The adjusted model has a comparative purpose with the usual proposals for delimiting management zones separately, so it was convenient to incorporate in the model a 3D weighting matrix relating the two relative depths recorded by the EM38MK2 sensor. By mapping the surface layer with the predictions of the SAC model, two distinguishable blocks were delimited in its ECa and management zone analyst (MZA), which can be suitable for experimentation or agricultural management. Research highlights: These results can be adopted to define the shape and dimension of the blocks in the context of experimental design so that with adequate blocking, the effect of spatial dependence associated with the physicochemical properties of soils related to ECa can be mitigated or suppressed.