Lattice Interaction Research Articles

Soft topological lattice wheels

We investigate the large deformation and extreme load-management capabilities of a soft topologically polarized kagome lattice mapped to a cylindrical domain through the problem of a lattice wheel rolling on an irregular surface. We test the surface–lattice interaction experimentally by subjecting a 3D-printed topological lattice wheel prototype to localized and distributed boundary loads. This investigation reveals a dichotomy in the force transfer between the two loading scenarios, whereby localized loads are absorbed with limited stress penetration into the bulk and small force transfer to the wheel axle, compared to distributed loads. Through numerical simulations, we compare the lattice wheel against a baseline solid wheel to highlight the unique stress management opportunities offered by the lattice configuration. These findings promote the design of rolling objects enabled by topological mechanics, in which a surplus of softness, activated by local asperities, can coexist with a globally stiff response to distributed loads that ensures satisfactory load-bearing capabilities.

Crystal structure, MEP/DFT/XRD, thione ⇔ thiol tautomerization, thermal, docking, and optical/TD-DFT studies of (E)-methyl 2-(1-phenylethylidene)-hydrazinecarbodithioate ligand

As small-molecule (E)-methyl 2-(1-phenylethylidene)hydrazinecarbodithioate has been prepared and characterized by X-ray single-crystal analysis. In order to elucidate the nature of the intermolecular interactions in the structural lattice, the Hirshfeld surface analysis (HSA) calculation was correlated to the XRD-packing result. Moreover, the XRD bond lengths and angles were compared to their DFT/B3LYP/6-311G(d,p) relative parameters. Considering the thione isomer as a kineticly favoured isomer, the single proton intra-migration from H-N to form S-H thionethiol tautomerization process was successfully computed via QST2 model. Additionally, Mulliken Atomic Charge (MAC), Natural Population Analysis (NPA), and Molecular Electrostatic Potential (MEP) analyses were carried out to confirm this process. The electron transfer and optical behavior of the ligand in DMSO have been exanimated with TD-DFT and HOMO/LUMO calculations. The thermal behavior of the compound was determined in an open room condition via TG/DTG. The two identified isomers of (E)-methyl 2-(1-phenylethylidene)-hydrazinecarbodithioate (thione and thiol forms) were docked against TcAChE (PDB:1EVE) revealed, conspicuous, different protein–drug structures, however, reflects identical docking scores (−7.2 Kcal/mol each), which is compared to the standard donepezil drug used in this study.

Stability of supercurrents in a superfluid phase of spin-1 bosons in an optical lattice

We study collective modes and superfluidity of spin-1 bosons with antiferromagnetic interactions in an optical lattice based on the time-dependent Ginzburg-Landau (TDGL) equation derived from the spin-1 Bose-Hubbard model. Specifically, we examine the stability of supercurrents in the polar phase in the vicinity of the Mott insulating phase with even filling factors. Solving the linearized TDGL equation, we obtain gapless spin-nematic modes and gapful spin-wave modes in the polar phase that arise due to the breaking of $S^2$ symmetry in spin space. Supercurrents exhibit dynamical instabilities induced by growing collective modes. In contrast to the second-order phase transition, the critical momentum of mass currents is finite at the phase boundary of the first-order superfluid-Mott insulator (SF-MI) phase transition. Furthermore, the critical momentum remains finite throughout the metastable SF phase and approaches zero towards the phase boundary, at which the metastable SF state disappears. We also study the stability of spin currents motivated by recent experiments for spinor gases. The critical momentum of spin currents is found to be zero, where a spin-nematic mode causes the dynamical instability. We investigate the origin of the zero critical momentum of spin currents and find it attributed to the fact that the polar state becomes energetically unstable even in the presence of an infinitesimal spin current. We discuss implications of the zero critical momentum of spin currents for the stability of the polar state.

DFT Calculations and Molecular Docking Studies on a Chromene Derivative

Chromenes and their derivatives have been considered as an important class of oxygen-containing heterocycles. There has been an increasing interest in the study of chromenes due to their biological activity. Herein, the structural, electronic, and vibrational properties of a chromene derivative, entitled 2‐amino‐5‐oxo‐4‐phenyl‐4,5‐dihydropyrano[3,2‐c]chromene‐3‐carbonitrile and abbreviated as Chrom-D, have been reported. The FT-IR, UV-vis, and 1H-NMR and 13C-NMR chemical shifts’ measurements were recorded. The molecular geometry and the vibrational frequencies are computed in the frame of density functional theory at the B3LYP/6-311++G(d,p) level of theory. The noncovalent interactions in the crystal lattice which are responsible to the 3D crystal structure of Chrom-D are investigated based on Hirshfeld surfaces and topological reduced density gradient (RDG) analysis. Molecular electrostatic potential surface, Mulliken charges, and Fukui functions are computed in order to find out the electrophilic and nucleophilic sites. The electronic properties of the title compound have been studied based on the TD-DFT calculations. Finally, Chrom-D has been evaluated as a multifunctional agent against Alzheimer’s disease (AD).

Synthesis and Characterization of a (-)-Epicatechin and Barbituric Acid Cocrystal: Single-Crystal X-ray Diffraction and Vibrational Spectroscopic Studies.

The paper presents the contribution of the cocrystallization method in the physicochemical modification of catechins that exhibit low oral bioavailability. This was done to obtain cocrystals for two naturally occurring polyphenolic diastereoisomers (+)-catechin and (−)-epicatechin with commonly used coformers. Due to distinct crystallization behavior, only the (−)-epicatechin cocrystal with barbituric acid in a 1:1 stoichiometry was obtained. The cocrystal of (−)-epicatechin (EC) with barbituric acid (BTA) was prepared by the slow solvent-evaporation technique. The structure and intermolecular interactions were determined by X-ray crystallographic techniques. The analysis of packing and interactions in the crystal lattice revealed that molecules in the target cocrystal were packed into tapes, formed by the O–H···O type contacts between the (−)-epicatechin and coformer molecules. The EC molecules interact with the carboxyl group in the BTA coformer mainly by −OH groups from the benzene ring A. The cocrystalline phase constituents were also investigated in terms of Hirshfeld surfaces. The application of Raman spectroscopy confirmed the involvement of the C=O group in the formation of hydrogen bonds between the (−)-epicatechin and barbituric acid molecules. Additionally, the solubility studies of pure EC and the EC-BTA cocrystal exhibited minor enhancement of EC solubility in the buffer solution, and pH measurements confirmed a stable level of solubility for EC and its cocrystal.

Spin-Twisted Optical Lattices: Tunable Flat Bands and Larkin-Ovchinnikov Superfluids.

Moiré superlattices in twisted bilayer graphene and transition-metal dichalcogenides have emerged as a powerful tool for engineering novel band structures and quantum phases of two-dimensional quantum materials. Here we investigate Moiré physics emerging from twisting two independent hexagonal optical lattices of atomic (pseudo-)spin states (instead of bilayers) that exhibit remarkably different physics from twisted bilayer graphene. We employ a momentum-space tight-binding calculation that includes all range real-space tunnelings and show that all twist angles θ≲6° can become magic and support gapped flat bands. Because of the greatly enhanced density of states near the flat bands, the system can be driven to superfluidity by weak attractive interaction. Strikingly, the superfluid phase corresponds to a Larkin-Ovchinnikov state with finite momentum pairing that results from the interplay between flat bands and interspin interactions in the unique single-layer spin-twisted lattice. Our work may pave the way for exploring novel quantum phases and twistronics in cold atomic systems.

Magnetoelectric effect in a single crystal of the frustrated spinel CoAl2O4

The magnetic ground state of $\mathrm{Co}{\mathrm{Al}}_{2}{\mathrm{O}}_{4}$ has been a controversial issue because the ratio of nearest- (${J}_{1}$) to next-nearest-neighbor (${J}_{2}$) exchange interactions in the diamond lattice is close to the boundary between a spiral spin liquid and a long-range ordered antiferromagnetic ground state. Recently, Ghara et al. reported a linear magnetoelectric effect in a polycrystalline $\mathrm{Co}{\mathrm{Al}}_{2}{\mathrm{O}}_{4}$ and attributed it to a long-range magnetic order. However, the magnetic ground state and the easy axis anisotropy remained unsolved. Here we propose the easy magnetic axis direction by comparing the results of magnetoelectric measurements in a high-quality single crystal with phenomenological calculations. From the value of polarization ratio $P||[1\text{\ensuremath{-}}10]$ measured under magnetic field applied along $H||[1\text{\ensuremath{-}}10]$ and $H||[001]$, we determined that the magnetic easy axis is along [111]. The single ion contribution of the magnetic ions located at the noncentrosymmetric environment is responsible for the magnetoelectric effect similar to that observed in other $A$-site magnetic spinel oxides, ${\mathrm{Co}}_{3}{\mathrm{O}}_{4}$, $\mathrm{Mn}{B}_{2}{\mathrm{O}}_{4}$ ($B=\mathrm{Al},\phantom{\rule{0.16em}{0ex}}\mathrm{Ga}$).

Harnessing oxygen vacancy in V2O5 as high performing aqueous zinc-ion battery cathode

Abstract Rechargeable aqueous zinc-ion batteries (ZIBs) have attracted considerable attention for large-scale energy storage systems due to their high energy density, low cost, and inherent safety. However, ZIBs suffer from limited cyclic stability with the use of the current cathode materials (such as V2O5) due to the strong electrostatic ion–lattice interactions with the diffusing divalent Zn2+, usually leading to a limited cyclic duration (

Magnetic interactions and the puzzling absence of any Raman mode in EuTiO3

AbstractPolycrystalline ceramic samples and a single crystal of EuTiO3 have been investigated by Raman spectroscopy in the temperature range 80–300 K. Although synchrotron x‐ray diffraction (XRD) data clearly indicated the cubic to tetragonal phase transition around 282 K, no mode from the symmetry allowed Raman active phonons was found in the tetragonal phase, contrary to the case of the homologous SrTiO3. In order to study the evolution of this unique characteristic, ceramics of EuxSr1‐xTiO3 (x = 0.03–1.0) characterized by synchrotron XRD for the structural phase transition have been also investigated by Raman spectroscopy, verifying the very strong influence on the Raman yield by Eu substitution. By applying an external magnetic field or alternatively hydrostatic pressure modes are activated in the Raman spectra. Temperature dependant XAS/XMCD measurements indicate the presence of magnetic interactions even close to room temperature in agreement with previous experimental results also showing the presence of small magnetic interactions deep inside the paramagnetic phase. A possible explanation for the puzzling absence of the Raman modes is proposed related to a strong spin–lattice interaction that drives the cubic to tetragonal structural phase transition and makes the Raman tensor antisymmetric. In this model, the external perturbation will induce a symmetric Raman tensor allowing modes to be present in the spectra.

Graphene on a hexagonal lattice substrate with on-site Hubbard interaction

We use the self-consistent mean field approach to study the dispersion relation of graphene on a substrate with hexagonal lattice structure, similar to that of graphene, taking into account on-site Hubbard interactions in the substrate sites. Different Hubbard interactions in the sublattices that constitute the substrate breaks the electron hole symmetry. The interaction between the substrate and the graphene sheet opens two gaps in the dispersion relation of graphene out of the Dirac K point. The position of the gaps depends on the ratio between the first neighbor interaction in graphene and the Hubbard on-site interaction in the substrate lattice.

Emergent Spin Dynamics Enabled by Lattice Interactions in a Bicomponent Artificial Spin Ice.

Artificial spin ice (ASI) networks are arrays of nanoscaled magnets that can serve both as models for frustration in atomic spin ice as well as for exploring new spin-wave-based strategies to transmit, process, and store information. Here, we exploit the intricate interplay of the magnetization dynamics of two dissimilar ferromagnetic metals arranged on complementary lattice sites in a square ASI to modulate the spin-wave properties effectively. We show that the interaction between the two sublattices results in unique spectra attributed to each sublattice, and we observe inter- and intralattice dynamics facilitated by the distinct magnetization properties of the two materials. The dynamic properties are systematically studied by angular-dependent broadband ferromagnetic resonance and confirmed by micromagnetic simulations. We show that combining materials with dissimilar magnetic properties enables the realization of a wide range of two-dimensional structures, potentially opening the door to new concepts in nanomagnonics.

Spectroscopic Signature of Spin–Charge–Lattice Coupling in CuB2O4

CuB2O4 has attracted considerable attention because of its unique chemical and physical properties and potential practical applications. In this paper, we investigated the optical properties of CuB2O4 single crystals through spectroscopic ellipsometry and Raman scattering spectroscopy. The optical absorption spectrum at room temperature revealed a direct band gap at approximately 3.88 ± 0.01 eV and two bands near 4.49 and 5.90 eV. The observed bands were related to charge transfer of electrons from the 2p states of the oxygen ions to the 3d states of the copper ions. The band gap exhibited unusual redshift with a decrease in temperature. Upon cooling across 21 K, which is the canted antiferromagnetic ordering temperature, the band gap, peak energy, and normalized intensity of charge-transfer bands presented anomalies. Furthermore, 38 phonon modes were identified in the room-temperature Raman scattering spectrum of CuB2O4. The phonon modes at approximately 335, 393, 403, 445, 473, 598, 706, 787, and 900 cm–1 exhibited softening below 21 K. The spin–phonon coupling constants were estimated to be 0.02–0.03 cm–1. These findings highlight a complex nature of spin–charge–lattice interactions in CuB2O4.

Influence of Dynamic Disorder and Charge–Lattice Interactions on Optoelectronic Properties of Halide Perovskites

The origins of many unique properties of halide perovskite semiconductors can be traced to charge–lattice interactions that lead to large polaron formation combined with their unusual electronic st...

Carrier transport and electron–lattice interactions of nonlinear optical crystals CdGeP2, ZnGeP2, and CdSiP2

Terahertz time-domain spectroscopy is employed to investigate temperature-dependent properties of bulk chalcopyrite crystals ( C d G e P 2 , Z n G e P 2 , and C d S i P 2 ). The complex spectra provide refraction and absorption as a function of temperature, from which electron–phonon coupling and average phonon energies are extracted and linked to the mechanics of the A- and B-site cations. AC conductivity spectra provide carrier densities and electron scattering times, the temperature dependence of which are associated with unintentional shallow dopants. Temperature dependence of the scattering time is converted into carrier mobility and modeled with microscopic transport mechanisms such as polar optical phonon, acoustic phonons, deformation potential, ionized impurity, and dislocation scattering. Hence, analysis links the terahertz optical and electronic properties to relate microscopic carrier transport and carrier–lattice interactions.

Effect of Polaron formation in conduction and dielectric behavior in La0.7Sr0.25K0.05MnO3 oxide

The purpose of this paper is to analyze the dielectric properties of La0.7Sr0.25K0.05MnO3 (LSKM) using impedance spectroscopy over the frequency range of 100 Hz to 1 MHz at different temperatures from 260 to 380 K. In fact, the dielectric analyses of the sample showed two relaxation processes at different relaxation times related to the effect of microstructural inhomogeneities and the contribution of grain and gain boundaries. However, Ac conductivity behavior reveals a metal–semiconductor phase transition at a specific temperature TM-S = 260 K and showed an important impact of the electron–lattice interaction in polaron formation. Also, the conductivity curve is analyzed by Johnscher’s universal power law and the variation of the exponent ‘n’ with temperature suggests the domination of small polaron hopping (SPH) model governed by an activation energy Ea = 0.12 eV. Further investigations using modulus formalism proved the presence of electrical relaxation, which is in good agreement with impedance results. The dielectric poly-dispersive behavior is related to the conduction process and the large value of the dielectric constant $$\varepsilon^{\prime\prime}(\omega )$$ in the order of 106 is correlated to the Maxwell–Wagner relaxation.

Ultrafast carrier and spin dynamics in GaMnAs across the Curie temperature

The carrier and spin dynamics of the diluted ferromagnetic semiconductor GaMnAs are crucial to understanding its ferromagnetic nature, especially near the Curie temperature (TC). Herein, transient differential reflectivity measurements and the temporal evolution of Kerr rotation are shown using ultrafast optical spectroscopy at various temperatures. The energy and angular momentum transfer routes after femtosecond laser pumping are revealed. The hole dynamics consist of two processes: a fast process that arises from carrier recombination and a slow process caused by carrier–lattice interactions. The spin dynamics are determined from the spin–orbital coupling and spin–lattice interactions in the ferromagnetic and paramagnetic phases, respectively. Critical phenomena are observed from the competition between the hole-mediated ferromagnetic orders and thermal perturbations near TC. These experimental results provide deep insights into the ultrafast decay behavior in GaMnAs, which is regarded as one of the most promising spintronic materials.

Superatomic Signature and Reactivity of Silver Clusters with Oxygen: Double Magic Ag 17 – with Geometric and Electronic Shell Closure

Understanding the stability and reactivity of silver clusters toward oxygen provides insights to design new materials of coinage metals with atomic precision. Herein, we report a systematic study o...

Moiré versus Mott: Incommensuration and Interaction in One-Dimensional Bichromatic Lattices.

Inspired by the rich physics of twisted 2D bilayer moiré systems, we study Coulomb interacting systems subjected to two overlapping finite 1D lattice potentials of unequal periods through exact numerical diagonalization. Unmatching underlying lattice periods lead to a 1D bichromatic "moiré" superlattice with a large unit cell and consequently a strongly flattened band, exponentially enhancing the effective dimensionless electron-electron interaction strength and manifesting clear signatures of enhanced Mott gaps at discrete fillings. An important nonperturbative finding is a remarkable fine-tuning effect of the precise lattice commensuration, where slight variations in the relative lattice periods may lead to a suppression of the correlated insulating phase, in qualitative agreement with the observed fragility of the correlated insulating phase in twisted bilayer graphene. Our predictions, which should be directly verifiable in bichromatic optical lattices, establish that the competition between interaction and incommensuration is a key element of the physics of moiré superlattices.

Torque equilibrium spin wave theory of Raman scattering in an anisotropic triangular lattice antiferromagnet with Dzyaloshinskii-Moriya interaction

We apply torque equilibrium spin wave theory (TESWT) to investigate an anisotropic XXZ antiferromagnetic model with Dzyaloshinskii-Moriya interaction in a triangular lattice. Considering the quasiparticle vacuum as our reference, we provide an accurate analysis of the noncollinear ground state of a frustrated triangular lattice magnet using the TESWT formalism. We elucidate the effects of quantum fluctuations on the ordering wave vector based on model system parameters. We study the single-magnon dispersion, the two-magnon continuum using the spectral function, and the Raman spectrum of bimagnon and trimagnon excitations. We present our results for the $HH,\phantom{\rule{0.28em}{0ex}}VV$, and the $HV$ polarization Raman geometry dependence of the bimagnon and trimagnon excitation spectra where $H\phantom{\rule{0.28em}{0ex}}(V)$ represents horizontal (vertical) polarization. Our calculations show that both the $HH$ and the $HV$ polarization spectra can be used to determine the degree of anisotropy of our system. We calculate the Raman spectra of ${\mathrm{Ba}}_{3}{\mathrm{CoSb}}_{2}{\mathrm{O}}_{9}$ and ${\mathrm{Cs}}_{2}{\mathrm{CuCl}}_{4}$.

Polarized and unpolarized phases of spin-orbit-coupled Bose-Einstein condensates in optical lattice

We investigate the phase transition of the Bose-Einstein condensates with equal-weight Rashba and Dresselhaus spin-orbit coupling trapped in one-dimensional optical lattice. Based on the variational and two-mode approximation, the critical condition for phase transition between polarized and unpolarized Bloch wave phase is obtained analytically for the first time, which explicitly reveals rich competitive relationship among spin-orbit coupling, optical lattice and atomic interactions in determining the phase transition of the system. It is shown that the change of the energy minima and the phase transition point by the optical lattice depends on the atomic interactions and spin-orbit coupling. Our results provide a theoretical evidence for deep understanding of the competition mechanism between the optical lattice and spin-orbit coupling for the ground state phase transition of spin-orbit-coupled Bose-Einstein condensates in optical lattice.