Quadrupole Research Articles

Revealing Mie Resonances with Enhanced and Suppressed Second‐Order Nonlinear Optical Responses in a Hexagonal‐Prism‐Like MoS2 Nanoparticle

AbstractTransition metal dichalcogenides (TMDC), such as molybdenum disulfide (MoS2), have attracted great interest owing to their excellent electronic and optical properties. Efficient second harmonic generation (SHG) has been successfully demonstrated in the MoS2 monolayer, in sharp contrast to the negligible SHG from the bulk material. Here, the nonlinear optical responses of hexagonal‐prism‐like MoS2 nanoparticles are investigated, which support Mie resonances in the near infrared spectral range. It is revealed that the Mie resonances of such a MoS2 nanoparticle can be clarified into two types, which exhibit enhanced and suppressed SHG. It is verified that the SHG from the MoS2 nanoparticle is strongly correlated with the electric field distribution at the optical resonance. For the electric quadrupole mode with an anti‐symmetric electric field distribution, the SHG is greatly suppressed. As a result, a nanohole appears in the emission pattern of the SHG from the MoS2 nanoparticle. In sharp contrast, the SHG from the electric dipole mode with a symmetric electric field distribution can be one order of magnitude stronger than that from a MoS2 monolayer. The findings open new horizons for manipulating the nonlinear optical responses of TMDC nanoparticles and pave the way for realizing photonic devices.

Directional characteristics of two gamelan gongs.

The distinctive geometry and structural characteristics of Balinese gamelan gongs lead to the instrument's unique sound and musical style. This work presents high-resolution directivity measurements of two types of gamelan gongs to quantify and better understand their acoustic behavior. The measured instruments' structural modes clearly impact their far-field directivity patterns, with the number of directional lobes corresponding to the associated structural mode shapes. Many of the lowest modes produce dipole-like radiation, with the dipole moment determined by the positions of the nodal and antinodal regions. Higher modes exhibit more complex patterns with multiple lobes often correlated with the location and number of antinodal regions on the gong's edge. Directivity indices correspond to dipole radiation at low frequencies and quadrupole radiation at intermediate and higher frequencies. Symmetry analysis confirms that the gong's rim significantly impacts the resultant directivity.

Robust and scalable rf spectroscopy in first-order magnetic sensitive states at second-long coherence time

Trapped-ion quantum sensors have become highly sensitive tools for the search of physics beyond the Standard Model. Recently, stringent tests of local Lorentz-invariance (LLI) have been conducted with precision spectroscopy in trapped ions (Pruttivarasin et al 2015 Nature 517 592–5, Megidish et al 2019 Phys. Rev. Lett. 122 123605, Sanner et al 2019 Nature 567 204–8, Dreissen et al 2022 Nat. Commun. 13 1–6) . We here elaborate on robust radio-frequency composite-pulse spectroscopy at second long coherence times in the magnetic sublevels of the long-lived state of a trapped 172Yb+ ion which is scalable to spatially extended multi-ion systems. We compare two Ramsey-type composite rf pulse sequences, a generalized spin-echo (GSE) sequence (Shaniv et al 2018 Phys. Rev. Lett. 120 103202) and a sequence based on universal rotations with 10 rephasing pulses (UR10) (Genov et al 2017 Phys. Rev. Lett. 118 133202) that decouple the energy levels from magnetic field noise, enabling robust and accurate spectroscopy. Both sequences are characterized theoretically and experimentally in the spin- electronic ground state of 172Yb+ and results show that the UR10 sequence is 38 (13) times more robust against pulse duration (frequency detuning) errors than the GSE sequence. We extend our simulations to the eight-level manifold of the state, which is highly sensitive to a possible violation of LLI, and show that the UR10 sequence can be used for high-fidelity Ramsey spectroscopy in noisy environments. The UR10 sequence is implemented experimentally in the manifold and a coherent signal of up to 2.5 s is reached. In (Dreissen et al 2022 Nat. Commun. 13 1–6) we have implemented this sequence and used it to perform the most stringent test of LLI in the electron–photon sector to date with a single Yb+ ion. Due to the high robustness of the UR10 sequence, it can be applied on larger ion crystals to improve tests of Lorentz symmetry further. We demonstrate that the sequence can also be used to extract the quadrupole moment of the meta-stable state, obtaining a value of which is in agreement with the value deduced from clock measurements (Lange et al 2020 Phys. Rev. Lett. 125 143201).

Microstrip dual band hybrid directional resonator antenna with volume reduction

This paper presents a novel design of a single-layer, horizontally polarized, dual-band, omni- and multi-directional hybrid dielectric resonator antenna (DRA) feeding through a 50 Ω coaxial connector. The proposed antenna consists of an FR4 substrate, a regular ground plane and a cross-shaped patch. The connector is placed at the middle point of the square ground plane. Above the microstrip patch, four similar solid dielectric resonator elements are placed diagonally. These DRA structures generate the TE111, hybrid HEM22δ modes and put up an ideal magnetic dipole and an electric quadrupole far-field radiation pattern. To verify the idea, an optimized antenna model is fabricated and tested. A reasonable agreement between the measured and simulated results is obtained. The measured impedance bandwidths of the TE111 and HEM22δ modes are 4.26 % (2.9–3.2 GHz) and 4.34 % (4.4–4.6 GHz), respectively. The proposed antenna has a stable omnidirectional radiation pattern at the first resonance frequency and a directional radiation pattern at the second resonance frequency and provides volume reduction.

Synchrotron emitting Komissarov torus around naked singularities

From a theoretical perspective, matter accretion processes around compact objects are highly relevant as they serve as a natural laboratory to test general relativity in the strong field regime. This enables us to validate fundamental concepts such as the no-hair theorem, the cosmic censorship hypothesis, and the existence of alternative solutions to Einstein’s equations that mimic the effects of black holes. In this study, we analyze the emission spectra of geometrically thick accretion disks, referred to as Polish doughnuts, around naked singularities described by the q-metric. To begin, we revisit the construction of equilibrium configurations of magnetized tori in this spacetime and evaluate the role of the deformation parameter over these configurations. Once we have systematically studied the disks in this spacetime, we use the OSIRIS code to perform a backward ray-tracing method, resulting in the first simulations of the intensity map and emission profiles of magnetized tori within this metric. Furthermore, we validate the effect of both the quadrupole moment and the angular momentum on observable quantities such as flux and intensity for optically thin and thick disks, since for values of q < 0, which correspond to objects with prolate deformation, and which in turn, are constructed with higher values of angular momentum, the emission spectrum exhibits higher intensity than that obtained for Schwarzschild’s spacetime. Hence, we find a first differential feature that distinguishes tori formed around naked singularities from those around static black holes.

Bound states in the continuum driven by multiple modes for high Q refractive index sensing in metasurfaces

Bound states in the continuum (BICs) have attracted much attention in the field of refractive index sensing. In this paper, we propose multi-mode symmetry-protected BICs (SP-BICs) and the Freidrich–Wintgen BIC (FW-BIC) in terahertz metasurfaces consisted of periodic open split ring resonators. Firstly, multi-mode SP-BICs are subject to the magnetic dipole, electric dipole (ED), and toroidal dipole (TD) modes. Moreover, we demonstrate the FW-BIC by strongly coupling the electric quadrupole and TD modes. For micron film sensing of the ED mode, simulation results show that the Q factor, the sensitivity of sensing (S), and the corresponding figure of merit can simultaneously reach 1561, 141 GHz/RIU, and 306, respectively. Our quasi-BICs have potential applications in micro-sensing.

Sea contribution to the charge radii and quadrupole moment of JP ½+, ³⁄₂+ baryons

Abstract An operator formalism is used on the wave function of baryons to compute their charge radii and quadrupole moments. The total anti-symmetric wave function in spin, color, and flavor space is framed for $J^P=\frac{1}{2}^+$ nucleons and $J^P=\frac{3}{2}^+$ hyperons. To understand the importance of the sea, a statistical model is used in conjugation with the detailed balance principle. Within the statistical approach, the importance of the sea with quarks and gluons are studied using the relevant probabilities that are associated with spin, flavor, and color space. The present work also focuses on individual contributions of valence and sea which contains terms of the scalar, vector, and tensor seas. The obtained results are in agreement with available theories and a few experimental outcomes. Our computed results may provide important information for upcoming experimental findings.

Density Functional Theory Calculations of Electronic Properties ,IR and UV-Vis Spectrum , Dipoles Moments ,and Atomic Charge Distribution of Mg 1-X Zn XFe2O4 Ferrite

Theoretical study using (Density Functional Theory) DFT method with B3LYP functional and the 3-21G(d,p) basis set had been implemented of calculating molecular structure properties of Magnesium – Zinc spinel ferrite having the chemical formula (Mg1-xZnxFe2O4). DFT had been used to optimize molecular structure, electronic state (HOMO-LUMO) , and electronic properties ( ionization potential, electronegativity, electron affinity, electrophilic, hardness, and softness) are calculated. Theoretical electronic IR spectrum were computed and plotted . UV-Vis spectrum calculated and plotted of this molecule. Dipole, Quadrupole, and Traceless Quadrupole moments were calculated. The Mullikan and Natural Bond Orbital (NBO) distribution of Mg1-xZnxFe2O4 compound are also computed by DFT. All these properties had been calculated using Gaussian09 program with Gauss view 5.08 program by using (Density Functional Theory) DFT method with 3-21G(d,p) basis set.

Electronic and structural behavior of graphene and azulphene nanoflakes under the influence of two-point charges

We have studied the behavior of graphene and azulphene nanoflakes in the presence of two-point charges. The carbon systems geometry was optimized using the DFT method without symmetry constraint. We studied the coronene (7-ring), two azulphene-coronenes (7-ring) with different symmetries, the superbenzene (19-ring), and three azulphene-superbenzenes (19-ring) with also different symmetries and different combinations of five, six, and seven-member rings exposed to an electric field due to two-point charges. In addition, the induced electric dipole and quadrupole were studied as a function of the charge point magnitude and signs.The Stark-lo-Surdo effect in HOMO, LUMO, and total energies was analyzed. The positive (negative) charges decrease (increase) the HOMO, LUMO, and total electronic energies. The contraction and expansion of molecular systems and the induced charge in the molecular plane due to two identical charges were studied. Due to two identical charges, the null net force does not deform the molecular systems out-off the xy-plane at z = 0. Instead, the deformation occurs in the xy-plane at z = 0, and the positive (negative) identical charges expand (contract) the molecular systems. These systems suffer concavation under the presence of the electric field due to two-point charges with opposite signs. The central ring is closer to the positive charge, while the hydrogen atoms belonging to the edges are closer to the negative charge for curved graphene models. The concavation of azulene-based systems is irregular and very intricate.This work aims to generically describe the influence of a pair of ions on the energetic and structural (electronic and geometric) components of two-dimensional carbon nanosystems with five, six, and seven-member rings. Our studies allow understanding of the general behavior to extrapolate to other bidimensional systems with different charge exposition like ions. Despite the complexity of the performance of the electric field due to point charges to systems with many electrons, we can obtain some general behaviors, although difficult to interpret in some cases.

Benchmarking calculations of excitation energies and transition properties with spectroscopic accuracy of highly charged ions used for the fusion plasma and astrophysical plasma

Atomic radiative data such as excitation energies, transition wavelengths, radiative rates, and level lifetimes with high precision are the essential parameters for the abundance analysis, simulation, and diagnostics in fusion and astrophysical plasmas. In this work, we mainly focus on reviewing our two projects performed in the past decade. One is about the ions with Z ≲ 30 that are generally of astrophysical interest, and the other one is about the highly charged krypton (Z = 36) and tungsten (Z = 74) ions that are relevant in research of magnetic confinement fusion. Two different and independent methods, namely, multiconfiguration Dirac–Hartree–Fock (MCDHF) and the relativistic many-body perturbation theory (RMBPT) are usually used in our studies. As a complement/extension to our previous works for highly charged tungsten ions with open M-shell and open N-shell, we also mainly focus on presenting and discussing our complete RMBPT and MCDHF calculations for the excitation energies, wavelengths, electric dipole (E1), magnetic dipole (M1), electric quadrupole (E2), and magnetic quadrupole (M2) transition properties, and level lifetimes for the lowest 148 levels belonging to the 3l 3 configurations in Al-like W61+. We also summarize the uncertainties of our systematical theoretical calculations, by cross-checking/validating our datasets from our RMBPT and MCDHF calculations, and by detailed comparisons with available accurate observations and other theoretical calculations. The data are openly available in Science Data Bank at https://doi.org/10.57760/sciencedb.10569.

Fully relativistic many-body perturbation energies, transition properties, and lifetimes of lithium-like iron Fe XXIV

Employing the advanced relativistic configuration interaction (RCI) combined with the many-body perturbation theory (RMBPT) method, we report energies and lifetime values for the lowest 35 energy levels from the (1s2)nl configurations (where the principal quantum number n = 2–6 and the angular quantum number l = 0,…,n–1) of lithium-like iron Fe XXIV, as well as complete data on the transition wavelengths, radiative rates, absorption oscillator strengths, and line strengths between the levels. Both the allowed (E1) and forbidden (magnetic dipole M1, magnetic quadrupole M2, and electric quadrupole E2) ones are reported. Through detailed comparisons with previous results, we assess the overall accuracies of present RMBPT results to be likely the most precise ones to date. Configuration interaction effects are found to be very important for the energies and radiative properties for the ion. The present RMBPT results are valuable for spectral line identification, plasma modeling, and diagnosing.

The spectroscopic quadrupole moment of the [formula omitted] state of 12C: A benchmark of theoretical models

The spectroscopic quadrupole moment of the first 2+ state of 12C has been measured employing the Coulomb-excitation re-orientation technique. Our result of Qs(21+)=+9.3−3.8+3.5efm2 suggests a larger oblate deformation than previously reported. Combining this with the consistently re-analyzed adopted value, we present the most precise value to date of Qs(21+)=+9.5(18)efm2, which is consistent with a geometrical rotor description. This simple outcome is compared to state-of-the-art shell-model, mean-field, ab initio calculations, cluster-based and geometrical-like theories, which show varying degrees of emergent quadrupole collectivity.

Polarizable atomic multipole-based force field for cholesterol

Cholesterol is one of the essential component of lipid in membrane. We present a polarizable atomic multipole force field (FF) for the molecular dynamic simulation of cholesterol. The FF building process follows the computational framework as the atomic multipole optimized energetics for biomolecular applications (AMOEBA) model. In this framework, the electronics parameters, including atomic monopole moments, dipole moments, and quadrupole moments calculated from ab initio calculations in the gas phase, are applied to represent the charge distribution. Furthermore, the many-body polarization is modeled by following the same pattern of distributed atomic polarizabilities. Then, the bilayers composed of two typical phospholipid molecules, 1,2-dimyristoyl-sn-glycero-3-phosphocholine (DMPC), and 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine (POPC), in a range of different cholesterol concentrations are built and implemented by molecular dynamics (MD) simulations based on the proposed polarizable FF. The simulation results are statistically analyzed to validate the feasibility of the proposed FF. The structural properties of the bilayers are calculated to compare with the related experimental values. The MD values show the same trend of experimental values changes. Communicated by Ramaswamy H. Sarma

A new mixed formalism based on SU(1,1) transition Hamiltonian in the investigation of deformed states and transition rates of 124Te

The existence of deformed states in nuclei such as 124Te leads to a change of the theoretical attitude to optimize the description of energy levels and electric quadrupole transition by using additional symmetries. The purpose of this contribution is to provide a detailed description of the energy gaps that appear in this nucleus using different mixing formalisms. To achieve this and also compare the accuracy of different formalisms, the transitional Hamiltonian in the affine SU(1,1) algebra was extended by adding the O(6)-Casimir operator. Also, the interacting boson model-2 is used to get theoretical predictions for the energy spectra and quadrupole transition rates of both regular and deformed states. Predictions of U(5) symmetry for the considered energy levels in 124Te nucleus show good agreement with experimental counterparts, except at 31+, 61+, and 62+ states where we tried to describe these levels by moving towards O(6) algebra. In this condition and using of both symmetries in the framework of mixing formalism, theoretical predictions for these deformed levels improved obviously, and transition probabilities were described in detail with high accuracy, too. Also, the IBM-2 suggests exact results for all regular states and intruder ones, and there are some suggestions about the advantages of each formalism in the description of energy levels and quadrupole transition rates of such nuclei.

Dual Control of Enhanced Quasi-Bound States in the Continuum Emission from Resonant c-Si Metasurfaces.

Optical bound states in the continuum (BICs) offer strong interactions with quantum emitters and have been extensively studied for manipulating spontaneous emission, lasing, and polariton Bose-Einstein condensation. However, the out-coupling efficiency of quasi-BIC emission, crucial for practical light-emitting devices, has received less attention. Here, we report an adaptable approach for enhancing quasi-BIC emission from a resonant monocrystalline silicon (c-Si) metasurface through lattice and multipolar engineering. We identify dual-BICs originating from electric quadrupoles (EQ) and out-of-plane magnetic dipoles, with EQ quasi-BICs exhibiting concentrated near-fields near the c-Si nanodisks. The enhanced fractional radiative local density of states of EQ quasi-BICs overlaps spatially with the emitters, promoting efficient out-coupling. Furthermore, coupling the EQ quasi-BICs with Rayleigh anomalies enhances directional emission intensity, and we observe inherent opposite topological charges in the multipolarly controlled dual-BICs. These findings provide valuable insights for developing efficient nanophotonic devices based on quasi-BICs.

The Structure of Terbium in the Ferromagnetic State.

Metals typically crystallize in highly symmetric structures due to their nondirectional and nonsaturated metallic bonds. Here, we report that terbium metal in its ferromagnetic state adopts an unusual low-symmetry orthorhombic structure with a Cmcm space group. A similar structure has been previously observed only in a few actinide metals with bonding 5f electrons at ambient pressure, such as uranium, neptunium, and plutonium, but with different nearest coordination numbers and bond-length variations. The Tb atom occupies the 4c site (0, ∼0.1661, 1/4), building up -[Tb-Tb]- layers stacking along the b-axis. Our first-principles many-body calculations of the crystal field splitting in the correlated Tb 4f-shell demonstrate that the Cmcm structure for ferromagnetic terbium is stabilized by magneto-elastic forces due to a secondary order of quadrupolar moments in the ferromagnetic state. These findings are significant for further understanding of the nature of terbium, including its electron structure, energy bands, phonons, and magnetism.

Toroidal electric dipole enabled chiral surface lattice resonances in stereo propeller metasurfaces

Surface lattice resonances (SLRs) are the coherent collective interactions between periodically arranged nanoparticles, which are generally considered to be formed by the resonant electric dipole, magnetic dipole, or electric quadrupole moments of a single nanoparticle coupled with the Rayleigh anomaly (RA). Here we reveal the first observation of the chiral SLRs that are formed by the coupling of the chiral toroidal electric dipole (TED) moment and RA mode through the theoretical design and experimental fabrication of a nano-kirigami based propeller metasurface. By engineering the rotational symmetry of the propeller, e.g., from C2 (C3) symmetry to C4 symmetry, we find that the electric dipole (electric quadrupolar) chiral SLRs have evolved into the TED associated chiral SLRs. Furthermore, it is found that the excitation amplitude of the TED moment can be tailored by controlling the stereo twisted height of the propeller and the spin of the incident light. Finally, the chiral TED moment enhanced circular dichroism is verified in the near-infrared wavelength region. Our study provides an effective yet simple scheme to manipulate the TED-dependent chiral SLRs, paving the way toward exploring the unconventional physical properties of TED and advanced chiroptical physics.

Hierarchical clinoptilolite zeolite-template carbon for highly selective separation of CO2 and CH4

BackgroundSeparating CO2 from natural gas before it is released into the atmosphere is a significant challenge in the present times due to its greenhouse effect. MethodsIn this study, a series of zeolite-template carbons (ZTCs) had been synthesized from acetylene as a carbon source using clinoptilolite as a template, through hydrofluoric acid etching and potassium hydroxide (KOH) activation processes. Significant findingsThe deposition of carbon on the zeolite-template was confirmed with different characterization techniques and their CO2 adsorption capacity and selectively toward methane (CH4) was evaluated at 25 °C, over a 1‒10 bar pressure range. The CO2/CH4 selectivity of the adsorbents was optimized with various synthesis parameters including chemical vapor deposition (CVD) reaction time, acetylene flow rate as well as activation temperature and KOH to carbon (KOH:C) mixing ratio. According to the findings, medium SBET (334.06 m2 g‒1), high Vtot (0.71 cm3 g‒1), high Vmeso (0.68 cm3 g‒1) and a large Dave (8.55 nm) of the ZTC-120–12.5–800–3 adsorbent (CVD reaction time of 120 min and acetylene flow rate of 12.5 cc min−1 as well as activation temperature of 800 °C and KOH:C ratio of 3:1) results in the highest CO2 capacity of 4.81 mmol g‒1 at 25 °C and 10 bar. Moreover, regarding the optimization goal of this study, the highest CO2/CH4 separation at 25 °C and 10 bar is the result of a long CVD reaction time (180 min), a high KOH:C ratio (4:1), a low acetylene flow rate (50 cc min‒1), and a low activation temperature (700 °C). In this regard, ZTC-180–50–700–4 showed the highest CO2/CH4 (15:85) selectivity of 13.35 with a high SBET (549.31 m2 g‒1), Vtot (0.718 cm3 g‒1), Vmicro/meso (15.6014), Vmeso (0.6211 cm3 g‒1) and a medium Dave (5.22 nm). The amine-functionalization of this sample increases the quadrupole moment between CO2 and nitrogen groups, and not only was the F-ZTC-180–50–700–4 sample's CO2 adsorption capacity increased by nearly 41% (4.11 mmol g‒1) compared to the ZTC-180–50–700–4 (2.91 mmol g‒1), but it also showed 58% higher CO2/CH4 selectivity (21.12). Based on the selectivity results of the functionalized ZTCs, their potential use in the separation of CO2 over CH4 at high pressures is demonstrated.

A Metamaterial Inspired Low-Scattering Electric Quadrupole Antenna

A Metamaterial Inspired Low-Scattering Electric Quadrupole Antenna

Multipole expansion of gravitational waves: memory effects and Bondi aspects

In our previous work, we proposed an algorithm to transform the metric of an isolated matter source in the multipolar post-Minkowskian approximation in harmonic (de Donder) gauge to the Newman-Unti gauge. We then applied this algorithm at linear order and for specific quadratic interactions known as quadratic tail terms. In the present work, we extend this analysis to quadratic interactions associated with the coupling of two mass quadrupole moments, including both instantaneous and hereditary terms. Our main result is the derivation of the metric in Newman-Unti and Bondi gauges with complete quadrupole-quadrupole interactions. We rederive the displacement memory effect and provide expressions for all Bondi aspects and dressed Bondi aspects relevant to the study of leading and subleading memory effects. Then we obtain the Newman-Penrose charges, the BMS charges as well as the second and third order celestial charges defined from the known second order and novel third order dressed Bondi aspects for mass monopole-quadrupole and quadrupole-quadrupole interactions.