Dipole Lattice Research Articles

A Frustrated Antipolar Phase Analogous to Classical Spin Liquids.

The study of magnetic frustration in classical spin systems is motivated by the prediction and discovery of classical spin liquid states. These uncommon magnetic phases are characterized by a massive degeneracy of their ground state implying a finite magnetic entropy at zero temperature. While the classical spin liquid state is originally predicted in the Ising triangular lattice antiferromagnet in 1950, this state has never been experimentally observed in any triangular magnets. The discovery of an electric analogue of classical spin liquids on a triangular lattice of uniaxial electric dipoles in EuAl12O19 is reported here. This new type of frustrated antipolar phase is characterized by a highly-degenerate state at low temperature implying an absence of long-range antiferroelectric order, despite short-range antipolar correlations. Its dynamics are governed by a thermally activated process, slowing down upon cooling toward a complete freezing at zerotemperature.

Multi-mode coupling in a H-shaped metamaterial structure in terahertz frequency

Mode coupling can not only effectively control the frequency, amplitude and linewidth of the transmission spectrum, but also improve the Q-factor of the spectrum. Herein, we propose a H-shaped metamaterial, in which the dipole mode, LC mode and lattice mode can be excited selectively, and each mode frequency can be independently tuned by changing the polarization of incident THz wave as well as the lattice constant of the metamaterial structure, thus allowing greater degrees of freedom to customize the polarization components of different properties in the system. Under different polarization directions, the strong coupling between the lattice mode and the inductance-capacitance (LC) mode as well as the lattice mode and the dipole mode is realized, which makes the transmission resonance Q-factor of the hybrid state increase to 8 times that of the single resonance state, and the obvious anti-crossing phenomenon is observed. In addition, the LC mode and the dipole mode can be excited simultaneously, and the coupling between these two modes successfully excites a bound states in the continuum with an infinite Q-factor.

Compression-induced crossovers for the ground state of classical dipole lattices on a Möbius strip.

We explore the ground-state properties of a lattice of classical dipoles spanned on the surface of a Möbius strip. The dipole equilibrium configurations depend significantly on the geometrical parameters of the Möbius strip, as well as on the lattice dimensions. As a result of the variable dipole spacing on the curved surface of the Möbius strip, the ground state can consist of multiple domains with different dipole orientations which are separated by domain-wall-like boundaries. We analyze in particular the dependence of the ground-state dipole configuration on the width of the Möbius strip and highlight two crossovers in the ground state that can be correspondingly tuned. A first crossover changes the dipole lattice from a phase which resists compression to a phase that favors it. The second crossover leads to an exchange of the topological properties of the two involved domains. We conclude with a brief summary and an outlook on more complex topologically intricate surfaces.

Ab initio generalized Langevin equation

We introduce a machine learning-based approach called ab initio generalized Langevin equation (AIGLE) to model the dynamics of slow collective variables (CVs) in materials and molecules. In this scheme, the parameters are learned from atomistic simulations based on ab initio quantum mechanical models. Force field, memory kernel, and noise generator are constructed in the context of the Mori-Zwanzig formalism, under the constraint of the fluctuation-dissipation theorem. Combined with deep potential molecular dynamics and electronic density functional theory, this approach opens the way to multiscale modeling in a variety of situations. Here, we demonstrate this capability with a study of two mesoscale processes in crystalline lead titanate, namely the field-driven dynamics of a planar ferroelectric domain wall, and the dynamics of an extensive lattice of coarse-grained electric dipoles. In the first case, AIGLE extends the reach of ab initio simulations to a regime of noise-driven motions not accessible to molecular dynamics. In the second case, AIGLE deals with an extensive set of CVs by adopting a local approximation for the memory kernel and retaining only short-range noise correlations. The scheme is computationally more efficient than molecular dynamics by several orders of magnitude and mimics the microscopic dynamics at low frequencies where it reproduces accurately the dominant far-infrared absorption frequency.

Ground states of one-dimensional dipolar lattice bosons at unit filling

Ground states of one-dimensional dipolar lattice bosons at unit filling

Geometry induced domain-walls of dipole lattices on curved structures

We investigate the ground state (GS) properties of rectangular dipole lattices on curved surfaces. The curved geometry can ‘distort’ the lattice and lead to dipole equilibrium configurations that strongly depend on the local geometry of the surface. We find that the system’s GS can exhibit domain-walls separating domains with different dipole configurations. Furthermore, we show how, regardless of the surface geometry, the domain-walls (DWs) locate along the lattice sites for which the (Euclidean) distances to nearest and next-nearest neighbors are equal. We analyze the response of the DWs to an external electric field and observe displacements and splittings thereof below and above a critical electric field, respectively. We further show that the DW acts as a boundary that traps low-energy excitations within a domain.

Lattice Mie resonances and emissivity enhancement in mid-infrared iron pyrite metasurfaces.

High-refractive-index antennas with characteristic dimensions comparable to wavelength have a remarkable ability to support pronounces electric and magnetic dipole resonances. Furthermore, periodic arrangements of such resonant antennas result in narrow and strong lattice resonances facilitated by the lattice. We design iron pyrite antennas operating in the mid-infrared spectral range due to the material's low-energy bandgap and high refractive index. We utilize Kirchhoff's law, stating that emissivity and absorptance are equal to each other in equilibrium, and we apply it to improve the thermal properties of the iron pyrite metasurface. Through the excitation of collective resonances and manipulation of the antenna lattice's period, we demonstrate our capacity to control emissivity peaks. These peaks stem from the resonant excitation of electric and magnetic dipoles within proximity to the Rayleigh anomalies. In the lattice of truncated-cone antennas, we observe Rabi splitting of electric and magnetic dipole lattice resonances originating from the antennas' broken symmetry. We demonstrate that the truncated-cone antenna lattices support strong out-of-plane magnetic dipole lattice resonances at oblique incidence. We show that the truncated-cone antennas, as opposed to disks or cones, facilitate a particularly strong resonance and bound state in the continuum at the normal incidence. Our work demonstrates the effective manipulation of emissivity peaks in iron pyrite metasurfaces through controlled lattice resonances and antenna design, offering promising avenues for mid-infrared spectral engineering.

Collective States in Molecular Monolayers on 2D Materials.

Collective excited states form in organic two-dimensional layers through Coulomb coupling of the molecular transition dipole moments. They manifest as characteristic strong and narrow peaks in the excitation and emission spectra that are shifted to lower energies compared with the monomer transition. We study experimentally and theoretically how robust the collective states are against homogeneous and inhomogeneous broadening, as well as spatial disorder that occurs in real molecular monolayers. Using a microscopic model for a two-dimensional dipole lattice in real space, we calculate the properties of collective states and their extinction spectra. We find that the collective states persist even for 1-10% random variation in the molecular position and in the transition frequency, with a peak position and integrated intensity similar to those for the perfectly ordered system. We measured the optical response of a monolayer of the perylene derivative MePTCDI on two-dimensional materials. On the wide-band-gap insulator hexagonal boron nitride, it shows strong emission from the collective state with a line width that is dominated by the inhomogeneous broadening of the molecular state. When the semimetal graphene is used as a substrate, however, the luminescence is completely quenched. By combining optical absorption, luminescence, and multiwavelength Raman scattering, we verify that the MePTCDI molecules form very similar collective monolayer states on hexagonal boron nitride and graphene substrates, but on graphene the line width is dominated by nonradiative excitation transfer from the molecules to the substrate. Our study highlights the transition from the localized molecular state of the monomer to a delocalized collective state in the two-dimensional molecular lattice that is entirely based on Coulomb coupling between optically active excitations of the electrons and molecular vibrations. The excellent properties of organic monolayers make them promising candidates for components of soft-matter optoelectronic devices.

Rigidity of dipolar coupled H2O molecular network in external electric field

We have performed the first study of the effect of an external electric field on the quantum paraelectric state of the electric dipolar lattice of polar water molecules confined within nano-sized cages of beryl crystal lattice. The complex dielectric permittivity ε* = ε'+iε" of a water subsystem in hydrous beryl is measured at frequencies 1 Hz-1 MHz in the temperature interval 10–300 K both in zero and 7 kV/cm external field. For comparison, we measure dielectric response of conventional quantum paraelectric KTaO3. In KTaO3, the application of electric field of several kV/cm suppresses quantum fluctuations and leads to a shallow maximum of ε′(T) around 15 K that could indicate a diffuse phase transition. In hydrous beryl, however, a bias electric field of up to 7 kV/cm has no effect on the dielectric response of the water molecules network. This result is confirmed by Monte Carlo simulations. We attribute the enhanced rigidity of the water dipolar subsystem to the strong long-range dipole-dipole interaction between separate H2O molecules. The field that could affect the polarization state of the dipoles is estimated to be of the order of 100 kV/cm.

Quantum Criticality and Universal Behavior in Molecular Dipolar Lattices of Endofullerenes

Fullerene cages allow the confinement of single molecules and the construction of molecular assemblies whose properties strongly differ from those of free species. In this work, we employ the density-matrix renormalization group method to show that chains of fullerenes filled with polar molecules (LiF, HF, and H2O) can form dipole-ordered quantum phases. In symmetry broken environments, these ordered phases are ferroelectric, a property that makes them promising candidates for quantum devices. We demonstrate that for a given guest molecule, the occurrence of these quantum phases can be enforced or influenced either by changing the effective electric dipole moment or by isotopic substitution. In the ordered phase, all systems under consideration are characterized by universal behavior that depends only on the ratio of the effective electric dipole and of the rotational constant. A phase diagram is derived, and further molecules are proposed as candidates for dipole-ordered endofullerene chains.

Preparation of Li2S-AlI3-LiI Composite Solid Electrolyte and Its Application in All-Solid-State Li-S Battery

Novel (80Li2S − 20AlI3)·yLiI composite solid electrolytes (y = 5, 10, 15) were prepared by mechannochemical synthesis. XRD results showed that the pattern of 80Li2S − 20AlI3 was similar to that of AlI3, which means that Li2S was dissolved in AlI3 matrix during preparation. This structure was still maintained after LiI addition. The current measured at constant applied DC voltage indicated that (80Li2S − 20AlI3)·yLiI composites are intrinsically pure Li-ion conductors. The ionic conductivity at 25 °C of y = 10 was about 2.3 × 10−4 Scm−1, which was about three times higher than that of y = 0. The conductivity of y = 10 increased 20 times to 2.2 × 10−3 Scm−1 at 70 °C. These values were highest among those observed from Li2S-based materials. It was revealed that Li-ion moves in 80Li2S − 20AlI3 by a hoping mechanism, while the lattice dipoles are the origin of Li-ion movement in (80Li2S − 20AlI3)·yLiI. The polarization measurements using Liǀ90 (80Li2S − 20AlI3)·10LiI ǀLi and LiǀLi6PS5Clǀ90 (80Li2S − 20AlI3)·10LiIǀLi6PS5ClǀLi cells proved that 90 (80Li2S − 20AlI3)·10LiI reacts with Li metal, but it is relatively stable at a low voltage. Sample y = 10 was also employed as a solid electrolyte in the positive electrode of a solid-state Li-S battery to study its stability in the voltage range of the positive electrode. CuS and Li4.4Si were the electrode-active materials. The cell was cycled in CC-CV mode at 1.0 mA cm−2 (CC) with a cut-off voltage of 1.0–2.3 V. The cell delivered a stable capacity of about 400 mAh g−1CuS after 40 cycles.

Polarization behavior in a compositionally graded relaxor–ferroelectric crystal visualized by angle-resolved polarized Raman mapping

Explaining the properties and functions of materials in terms of their atomic arrangements and inhomogeneous structures is a fundamental challenge for the development of ferroelectric oxides. Dielectric response, a fundamental property of matter, can be explained by long-wavelength polar lattice vibrations and dipole relaxations capable of responding to electrical bias; therefore spectroscopic methods, such as Raman spectroscopy, can be used to investigate its origin. Herein, we used angle-resolved polarized Raman mapping to investigate how phase boundaries and giant dielectric responses are related in a relaxor-Pb(Mg1/3Nb2/3)O3–ferroelectric-PbTiO3 (PMN-xPT) solid-solution system using a compositionally graded crystal, with gradual changes in polarization direction visualized by Raman mapping. The variation of the width of quasielastic light scattering with position reveals the following: The huge dielectric response observed in PMN-xPT is ascribable to the slowing down of a relaxation related to mesoscopic ferroelectric domains near the phase boundary, which is characteristic of relaxor–ferroelectric solid-solution systems and differentiates them from other ferroelectrics.

Large Optical Modulation of Dielectric Huygens’ Metasurface Absorber (Advanced Optical Materials 10/2023)

Mie-type optical resonators are applicable to all-optical modulation. In article number 2300102, Hao-Yu Cheng, Kung-Hsuan Lin, Kuo-Ping Chen, and co-workers demonstrate both theoretically and experimentally that modulation depth is enhanced by two orders of magnitude in Huygens' metasurface absorber where electric dipole lattice resonance matches the magnetic dipole resonance. Within picosecond scale delay after ultrafast photoexcitation and a few square micrometer spatial confinement, over 100% photothermal modulation depth is experimentally achieved in Huygens' metasurface absorber based on amorphous silicon.

Modular development of deep potential for complex solid solutions

The multicomponent oxide solid solution is a versatile platform to tune the delicate balance between competing spin, charge, orbital, and lattice degrees of freedom for materials design and discovery. The development of compositionally complex oxides with superior functional properties has been largely empirical and serendipitous, in part due to the exceedingly complex chemistry and structure of solid solutions that span a range of length scales. The usage of classical molecular dynamics (MD), a powerful statistical method, in computer-aided materials design has not yet reached the same level of sophistication as that in computer-aided drug design because of the limited availability and accuracy of classical force fields for solids. Here, we introduce the strategy of ``modular development of deep potential'' (ModDP) that enables a systematic development and improvement of deep-neural-network-based model potential, termed as deep potential, for complex solid solutions with minimum human intervention. The converged training database associated with an end-member material is treated as an independent module and is reused to train the deep potential of solid solutions via a concurrent learning procedure. We apply ModDP to obtain classical force fields of two technologically important solid solutions, ${\mathrm{Pb}}_{x}{\mathrm{Sr}}_{1\ensuremath{-}x}{\mathrm{TiO}}_{3}$ and ${\mathrm{Hf}}_{x}{\mathrm{Zr}}_{1\ensuremath{-}x}{\mathrm{O}}_{2}$. For both materials' systems, a single model potential is capable of predicting various properties of solid solutions including temperature-driven and composition-driven phase transitions over a wide range of compositions. In particular, the deep potential of ${\mathrm{Pb}}_{x}{\mathrm{Sr}}_{1\ensuremath{-}x}{\mathrm{TiO}}_{3}$ reproduces a few known topological textures such as polar vortex lattice and electric dipole waves in ${\mathrm{PbTiO}}_{3}/{\mathrm{SrTiO}}_{3}$ superlattices, paving the way for MD investigations on the dynamics of topological structures in response to external stimuli. MD simulations of ${\mathrm{Hf}}_{x}{\mathrm{Zr}}_{1\ensuremath{-}x}{\mathrm{O}}_{2}$ reveal a substantial impact of composition variation on both the phase transition temperature and the nature of the high-temperature nonpolar phase.

Large Optical Modulation of Dielectric Huygens’ Metasurface Absorber

AbstractHigh‐index nanostructures are found to exhibit large nonlinearity of spectral responses under photoexcitation, which is applicable to all‐optical modulation. The nonlinearity stems from Mie‐type resonance shift due to photoinduced variation of refractive index. Here, amorphous silicon‐based Huygens’ metasurface absorber and ultrafast excitation are used to demonstrate two orders of magnitude enhancement of modulation depth, both theoretically and experimentally, when electric dipole lattice resonance matches the magnetic dipole resonance. Within a few square micrometer spatial confinement and picosecond scale delay, over 100% photothermal modulation depth is experimentally achieved at matched resonance condition. This concept is not limited to photothermal modulation in the amorphous silicon but is applicable to dielectric materials with various mechanisms to achieve modulation of refractive index. This work opens the avenue toward all‐optical information processing via optimized modulation by careful spatiotemporal and spectral control over a metasurface.

Magnetic solitons due to interfacial chiral interactions

We study solitons in a zig-zag lattice of magnetic dipoles. The lattice comprises two sublattices of parallel chains with magnetic dipoles at their vertices. Due to orthogonal easy planes of rotation for dipoles belonging to different sublattices, the total dipolar energy of this system is separable into a sum of symmetric and chiral long-ranged interactions between the magnets where the last takes the form of Dzyaloshinskii–Moriya (DM) coupling. For a specific range of values of the offset between sublattices, the dipoles realize an equilibrium magnetic state in the lattice plane, consisting of one chain settled in an antiferromagnetic (AF) parallel configuration and the other in a collinear ferromagnetic fashion. If the offset grows beyond this value, the internal DM field stabilizes two Bloch domain walls at the edges of the AF chain. The dynamics of these solitons is studied by deriving the long-wavelength lagrangian density for the easy axis antiferromagnet. We find that the chiral couplings between sublattices give rise to an effective magnetic field that stabilizes the solitons in the antiferromagnet. When the chains displace respect to each other, an emergent Lorentz force accelerates the domain walls along the lattice.

Intrinsic chiral field as vector potential of the magnetic current in the zig-zag lattice of magnetic dipoles

Chiral magnetic insulators manifest novel phases of matter where the sense of rotation of the magnetization is associated with exotic transport phenomena. Effective control of such phases and their dynamical evolution points to the search and study of chiral fields like the Dzyaloshinskii–Moriya interaction. Here we combine experiments, numerics, and theory to study a zig-zag dipolar lattice as a model of an interface between magnetic in-plane layers with a perpendicular magnetization. The zig-zag lattice comprises two parallel sublattices of dipoles with perpendicular easy plane of rotation. The dipolar energy of the system is exactly separable into a sum of symmetric and antisymmetric long-range exchange interactions between dipoles, where the antisymmetric coupling generates a nonlocal Dzyaloshinskii–Moriya field which stabilizes winding textures with the form of chiral solitons. The Dzyaloshinskii–Moriya interaction acts as a vector potential or gauge field of the magnetic current and gives rise to emergent magnetic and electric fields that allow the manifestation of the magnetoelectric effect in the system.

Influence of flight mode on loads from turbulent air

This paper investigated the influence of altitude and flight speed on the loads arising on the elastic wing of a turbojet aircraft of conventional layout, which falls into turbulent conditions. The aircraft structure is modeled by elastic beams with appropriate weight and stiffness distribution. Performed a modal analysis of the aircraft design and examined the influence of the number of calculated tones own oscillations on the loading of an aircraft wing. Aerodynamic forces and moments are determined by the dipole lattice and constant pressure method (DLM/CPM). Non-stationary characteristics are also taken into account, as required by certification specification. Determining the effect of flight speed showed the need to consider both the minimum and maximum speeds, because at minimum speed the end zone of the wing is loaded more, and at the cruise speed ‒ the root section. When analyzing the effect of flight altitude on the load, determined that the maximum values of transverse force and bending moment occur when flying at minimum altitude, and the torque on the wing reaches the maximum value at altitudes with the maximum Mach number. Separately highlighted loads of aircraft wing at horizontal balanced flight. Also showed that the speed of flight, namely the Mach number, significantly affects the torque that occurs on the wing.

Staggered quantum phases of dipolar bosons at finite temperatures

The extended Bose-Hubbard model with correlated tunneling exhibits staggered superfluid and supersolid quantum phases. We study finite-temperature phase transitions of quantum phases of dipolar bosons in a two-dimensional optical lattice using Gutzwiller mean-field and quantum Monte Carlo approaches. When nearest-neighbor repulsion is comparable to the on-site interaction, we find that the two topologically distinct superfluids are separated by a normal-fluid phase, while at stronger off-site interactions, density-modulated insulating quantum phases appear. We estimate the critical temperature of the staggered-superfluid to normal-fluid transition and show that this transition is of the Kosterlitz-Thouless type. Finally, we elucidate the coexistence of staggered quantum phases in the presence of an external trapping potential. Our study paves the way to observe novel staggered quantum phases in dipolar optical lattice experiments.

Theoretical insights into the Peierls plasticity in SrTiO3 ceramics via dislocation remodelling

An in-depth understanding of the dislocations motion process in non-metallic materials becomes increasingly important, stimulated by the recent emergence of ceramics and semiconductors with unexpected room temperature dislocation-mediated plasticity. In this work, local misfit energy is put forward to accurately derive the Peierls stress and model the dislocation process in SrTiO3 ceramics instead of the generalized stacking fault (GSF) approach, which considers the in-plane freedom degrees of the atoms near the shear plane and describes the breaking and re-bonding processes of the complex chemical bonds. Particularly, we discover an abnormal shear-dependence of local misfit energy, which originates from the re-bonding process of the Ti-O bonds and the reversal of lattice dipoles. In addition, this approach predicts that oxygen vacancies in the SrTiO3 can facilitate the nucleation and activation of dislocations with improvement of fracture toughness, owing to the reduction of average misfit energy and Peierls stress due to the disappearance of lattice dipole reversal. This work provides undiscovered insights into the dislocation process in non-metallic materials, which may bring implications to tune the plasticity and explore unknown ductile compositions.