Dipolar Nature Research Articles

Inference of the cosmic rest-frame from supernovae Ia

We determine the proper motion of the Solar System from the Pantheon sample of type Ia supernovae (SNe). The posterior distribution of the Solar System proper velocity, its direction, and relevant cosmological parameters were obtained based on the observed distance moduli, heliocentric redshifts, and positions of SNe by means of a Markov chain Monte Carlo method. We accounted for the unknown peculiar motion of SNe by including their expected covariance from linear theory. We find that the Solar System moves with vo = 249 ± 51 km s−1 towards RA = 166 ± 16 deg, Dec = 10 ± 19 deg (J2000), (all at 68% C.L.). The direction of motion agrees with the direction of the dipole observed in the cosmic microwave background (CMB) (RA = 166 deg, Dec = −7 deg). The inferred velocity is 2.4σ lower than the value inferred from a purely kinematic interpretation of the CMB dipole (370 km s−1). Assuming a flat Λ cold dark matter model, we find no degeneracy of solar proper motion with other cosmological parameters. The dimensionless matter density, ΩM = 0.305 ± 0.022, is in excellent agreement with CMB measurements. We also find no degeneracy of the solar proper motion with the SN calibration nuisance parameter. Bulk flows might be able to explain why the solar motion appears to be slower than that of nearby SNe. We conclude that a larger sample of SNe, distributed over wide areas of the sky and a broad range in redshift, will allow an independent and robust test of the kinematic nature of the CMB dipole.

Interpretation of the magnetic anomalies over the Mid-Atlantic Ocean Ridge using Swarm-A satellite

The procedures and interpretation of the magnetic data measured over the Mid-Atlantic Ocean Ridge by Swarm-A satellite is discussed in this paper. The data processing procedure has four phases after the data format conversion. The first phase is the selecting data whose Kp index is lower than 1. Secondly, the main magnetic field should be subtracted from the measured data for example through the IGRF model. This step is followed by removing trend, related to the satellite trajectory. The final step is eliminating the dipole nature of the magnetic field via Reduction to the Pole (RTP). Nonetheless, the RTP process might cause misinterpretation over the large study area and lower latitudes. Therefore, the amplitude of the analytic signal (AS) is used as an alternative to the RTP. The qualitative interpretation of the magnetic anomaly is conducted via AS anomaly, bathymetry, heat flow and tectonic map. Quantitatively correlation coefficients of bathymetry and heat flow with respect to AS are interpreted.

Small mode volume topological photonic states in one-dimensional lattices with dipole-quadrupole interactions

We study the topological photonic states in one-dimensional lattices analog to the Su-Schrieffer-Heeger model beyond the dipole approximation. The electromagnetic resonances of the lattices supported by near-field interactions between the plasmonic nanoparticles are studied analytically with coupled dipole-quadrupole method. The topological phase transition in the bipartite lattices is determined by the change of Zak phase. Our results reveal the contribution of quadrupole moments to the near-field interactions and the band topology. It is found that the topological edge states in nontrivial lattices have both dipolar and quadrupolar nature. The quadrupolar edge states are not only orthogonal to the dipolar edge states, but also spatially localized at different sublattices. Furthermore, the quadrupolar topological edge states, which coexist at the same energy with the quadrupolar flat band have shorter localization length and hence smaller mode volume than the conventional dipolar edge states. The findings deepen our understanding in topological systems that involve higher-order multipoles, or in analogy to the wave functions in quantum systems with higher-orbital angular momentum, and may be useful in designing topological systems for confining light robustly and enhancing light-matter interactions.

Probing the rest-frame of the Universe with the near-IR cosmic infrared background

ABSTRACT While the cosmic microwave background (CMB) dipole is largely assumed to be entirely kinematic, there is evidence that part of it is primordial. Such a possibility arises in models implying a tilt, interpreted as a dark flow, across the observable Universe. The kinematic nature of the entire CMB dipole can be probed using the dipole of cosmic backgrounds from galaxies after the last scattering. The near-infrared (near-IR) cosmic infrared background (CIB) spectral energy distribution leads to an amplified dipole compared with the CMB. The CIB dipole is affected by galaxy clustering, decreasing with fainter, more distant galaxies, and by Solar System emissions and Galactic dust, which dominate the net CIB cosmological dipole in the optical/near-IR. We propose a technique that enables an accurate measurement of the kinematic near-IR CIB dipole. The CIB, effectively the integrated galaxy light (IGL), would be reconstructed from resolved galaxies in forthcoming space-borne wide surveys covering four bands, 0.9–2.5 μm. The galaxies will be subselected from the identified magnitude range where the dipole component from galaxy clustering is below the expected kinematic dipole. Using this technique, the dipole can be measured in each of the bands at the statistical signal-to-noise ratio S/N ≳50–100 with the forthcoming Euclid and Roman surveys, isolating the CMB dipole’s kinematic nature.

Temperature-sensitive spin-wave nonreciprocity induced by interlayer dipolar coupling in ferromagnet/paramagnet and ferromagnet/superconductor hybrid systems

Spin-wave (SW) spectra have theoretically been studied in a thin film of a ferromagnet (FM) on a substrate from a paramagnet (PM) (an FM above the critical temperature) or from superconductor (SC). A spin wave propagating in the FM induces the dynamic magnetization and superconducting current in the underlying PM and SC, respectively, which affect the SW propagation by their magnetic fields. As a result of this interaction, the SW spectrum becomes nonreciprocal to depend on the sign of the SW wave vector q. We show that the nonreciprocal contribution to the SW spectra in FM/PM and FM/SC systems is given by the frequency shift of {\Delta}{\omega}(q)={\omega}(q)-{\omega}(-q)=a(T)({\tau}{\cdot}q) with {\tau}=(n{\times}M) being the toroidal magnetic moment, M the FM magnetization, n the unit vector normal to the FM/PM(SC) interface, and a(T) the temperature-dependent constant of a dipole nature, whose sign depends on the substrate type. As the {\Delta}{\omega}(T) dependence is strong at temperatures T close to the critical temperature Tc for the FM-PM or normal metal-SC transition, one gets a possibility to control the frequency SW nonreciprocity with temperature variation near Tc. The dipolar mechanism we propose for SW frequency nonreciprocity is promising for introducing this property of SW propagation into functional devices.

C2H5NO Isomers: From Acetamide to 1,2-Oxazetidine and Beyond.

This work documents the properties of a number of isomers of molecular formula C2H5NO from the most stable, acetamide, through 1,2-oxazetidine and including even higher energy species largely of a dipolar nature. Only two of the isomers have been detected in emissions from the interstellar medium (ISM); possible further candidates are identified, and the likelihood of their being detectable is considered. In general, hardly any of these compounds have been discussed in the existing chemical literature, so this work represents an important contribution extending the canon of chemical bonding which can contribute to machine learning, providing a more exacting test of AI applications. The presence in the ISM of acetamide, CH3C(O)NH2, is the subject of current debate with no clear and obvious paths to its formation; it is shown that a 1,3-[H]-transfer from (E,Z)-ethanimidic acid, CH3C(OH)=NH, is feasible in spite of an energy barrier of 130 kJ mol–1. It is speculated that imidic acid can itself be formed from abundant precursors, H2O and CH3C≡N, in an acid-induced, water addition, autocatalytic reaction on water–ice grains. H3CC≡NH3CC≡NH+ + H2OH3CC(O+H2)=NHH3CC(OH)=NH + H3O+

Theoretical exploration of 1,3-Indanedione as electron acceptor-cum-anchoring group for designing sensitizers towards DSSC applications

The present work highlights the DFT and TD-DFT calculations of a few organic sensitizers designed based on a new electron-acceptor, 1,3-indanedione, which is a well-known electron-acceptor for designing new electron donor–acceptor molecules. Nine organic sensitizers (GR1-9) have been designed based on a modified 1,3-indanedione electron-acceptor and conventional electron-donor moieties. Optimization studies reveal that all dyes have twisted configurations, and therefore, the aggregation on the TiO2 semiconductor is expected to be less. GR2 dye shows the smallest energy gap, 2.43 eV, as compared to others which indicates an effective electronic excitation and injection. The dyes’ energy levels are compatible with the conduction band of TiO2 and redox potentials of the redox couple. Thermodynamic parameters indicate that the GR1, GR2, and GR5 dyes regenerate at a faster rate as compared to the other dyes. Further, NBO calculations demonstrate the dipolar nature of the designed molecules. Electronic spectra of dyes were red-shifted by 18–29 nm in acetonitrile solvent, which shifts further towards red-region upon adsorbing on to titania. The absorption spectrum of the GR1@TiO2 system shows a remarkable shift, 92 nm, and extends to the NIR region. The electron density of LUMO and LUMO + 1 is majorly confined to TiO2 moiety upon binding, which indicates complete electron donation from dye to the TiO2. Overall, our studies reveal that the 1,3-indanedione skeleton has the potential to serve as an electron-acceptor in designing new organic sensitizers for DSSCs. Therefore by conjugating conventional electron-donors with the 1,3-indanedione electron-acceptor, a new class of organic sensitizers can perhaps be synthesized for DSSC applications.

Direct Observation of the Charge Transfer States from a Non-Fullerene Organic Solar Cell with a Small Driving Force.

For organic solar cells (OSCs), the charge generation mechanism and the recombination loss are heavily linked with charge transfer states (CTS). Measuring the energy of CTS (ECT) by the most widely used technique, however, has become challenging for the non-fullerene-based OSCs with a small driving force, resulting in difficulty in the understanding of OSC physics. Herein, we present a study of the PM6:Y6 bulk heterojunction. It is demonstrated that electro-absorption can not only reveal the dipolar nature of Y6 but also resolve the morphology-dependent absorption signal of CTS in the sub-bandgap region. The device with the optimum blending weight ratio shows an ECT of 1.27 eV, which is confirmed by independent measurements. Because of the charge transfer characteristics of Y6, the charge generation at PM6:Y6 interfaces occurs efficiently under a small but non-negligible driving force of 0.14 eV, and the total recombination loss is as low as 0.43 eV.

Thermally active nanoparticle clusters enslaved by engineered domain wall traps

The stable assembly of fluctuating nanoparticle clusters on a surface represents a technological challenge of widespread interest for both fundamental and applied research. Here we demonstrate a technique to stably confine in two dimensions clusters of interacting nanoparticles via size-tunable, virtual magnetic traps. We use cylindrical Bloch walls arranged to form a triangular lattice of ferromagnetic domains within an epitaxially grown ferrite garnet film. At each domain, the magnetic stray field generates an effective harmonic potential with a field tunable stiffness. The experiments are combined with theory to show that the magnetic confinement is effectively harmonic and pairwise interactions are of dipolar nature, leading to central, strictly repulsive forces. For clusters of magnetic nanoparticles, the stationary collective states arise from the competition between repulsion, confinement and the tendency to fill the central potential well. Using a numerical simulation model as a quantitative map between the experiments and theory we explore the field-induced crystallization process for larger clusters and unveil the existence of three different dynamical regimes. The present method provides a model platform for investigations of the collective phenomena emerging when strongly confined nanoparticle clusters are forced to move in an idealized, harmonic-like potential.

Dipolar particles via photopolymerization of 1,6-hexanediol diacrylate miniemulsion template tailored with oppositely-charged polymerizable surfactants

A new technique was developed for producing dipolar colloidal particles via miniemulsification of 1,6-hexandiol diacrylate (HDDA), which was stabilized by a non-ionic surfactant, in presence of a UV initiator, and doped with different oppositely-charged polymerizable surfactants (surfmers). The surfmers were chosen of poor miscibility with water to ensure their existence at the interface between the phases while the charged moieties are exposed toward the aqueous phase. Thereafter, the miniemulsion was mixed with agarose medium, and gelation was accomplished instantly to arrest the oil drops while the charged surfmers are immobilized on their surfaces. The drops were exposed to DC-field for polarization of the charges whereas UV radiation was applied simultaneously to trigger polymerization. The well-known particle nucleation in miniemulsion systems as well as polarizability of the charged moieties of the surfmers under the effect of the field and complete conversion of UV-initiated polymerization allowed the formation of particles bearing strong dipole moment. Size and zeta potential measurements of particles confirmed the nanometric size, typical of miniemulsion technique, which was further confirmed by scanning electron microscopy (SEM). On the other hand, a net charge on the surface even in presence of both cationic and anionic surfmers, is an evidence of non-equal hemispheres of the particles under the alignment induced by the electric field. This is dependent on the molar ratio of the charged species and intensity of the electric field during polymerization. In addition, the high resistance of aqueous dispersions of the polarized particles to induced aggregation in presence of an electrolyte, compared to a weakly-polarized comparable system, approves strongly the dipolarity of the particles. Cross-polarized optical imaging of assemblies formed in presence of electrolytes indicated clusters around 30 µm in size with excellent birefringence. Nevertheless, that was not the case for the un/weakly-polarized particles, indicating the anisotropy of the particles that agrees with the expected dipolar nature. This was also supported by SEM images recorded after DC induced polarization, which showed ordered aggregates in response to the applied DC field on particles holding aligned opposite charges.

Comparison of closed-form solutions to experimental magnetic force between two cylindrical magnets

The force between permanent magnets implemented in many engineering devices remains an intriguing problem in basic physics. The variation of magnetic force with the distance x between a pair of magnets cannot usually be approximated as x-4 because of the dipole nature and geometry of magnets. In this work, the force between two identical cylindrical magnets is accurately described by a closed-form solution. The analytical model assumes that the magnets are uniformly magnetized along their length. The calculation, based on the magnetic field exerted by one magnet on the other along the direction of their orientation, shows a reduction in the magnetic force with the distance x and a dependence on the size parameters of magnets. To verify the equation, the experiment was set up by placing two cylindrical neodymium iron boron type magnets in a vertical tube. The repulsive force between the identical upper and lower magnets of 2.5 cm in diameter and 7.5 cm in length was measured from the weight on the top of the upper magnet. The resulting separation between the magnets was recorded as x. The forces measured at x=0.004-0.037 m differ from the values calculated using the analytic solution by -0.55 % to -13.60 %. The calculation also gives rise to a practical remnant magnetic field of 1.206 T. When x is much large than the equation of force is approximated as a simple form proportional to 1/x-4. The finding can be directly used in magnetic levitation as well as applied in calculating magnetic fields and forces in other systems incorporating permanent magnets.

Proposed rapid detection of nuclear spins with entanglement-enhanced sensors

Recently, there have been significant developments to detect nuclear spins with nitrogen vacancy (NV) centers in diamond. However, due to the nature of the short range dipole–dipole interaction, it takes a long time to detect distant nuclear spins with the NV centers. Here, we propose a rapid detection of nuclear spins with an entanglement between the NV centers. We show that the necessary time to detect the nuclear spins with the entanglement is several orders of magnitude shorter than that with separable NV centers. Our results pave the way for new applications in nanoscale nuclear magnetic resonance spectroscopy.

Self-Organization in Cold Atoms Mediated by Diffractive Coupling

This article discusses self-organization in cold atoms via light-mediated interactions induced by feedback from a single retro-reflecting mirror. Diffractive dephasing between the pump beam and the spontaneous sidebands selects the lattice period. Spontaneous breaking of the rotational and translational symmetry occur in the 2D plane transverse to the pump. We elucidate how diffractive ripples couple sites on the self-induced atomic lattice. The nonlinear phase shift of the atomic cloud imprinted onto the optical beam is the parameter determining coupling strength. The interaction can be tailored to operate either on external degrees of freedom leading to atomic crystallization for thermal atoms and supersolids for a quantum degenerate gas, or on internal degrees of freedom like populations of the excited state or Zeeman sublevels. Using the light polarization degrees of freedom on the Poincaré sphere (helicity and polarization direction), specific irreducible tensor components of the atomic Zeeman states can be coupled leading to spontaneous magnetic ordering of states of dipolar and quadrupolar nature. The requirements for critical interaction strength are compared for the different situations. Connections and extensions to longitudinally pumped cavities, counterpropagating beam schemes and the CARL instability are discussed.

Polarization dependent beaming properties of a plasmonic lattice laser

We study beaming properties of laser light produced by a plasmonic lattice overlaid with organic fluorescent molecules. The crossover from spontaneous emission regime to stimulated emission regime is observed in response to increasing pump fluence. This transition is accompanied by a strong reduction of beam divergence and emission linewidth due to increased degree of spatial and temporal coherence, respectively. The feedback for the lasing signal is shown to be mainly one-dimensional due to the dipolar nature of the surface lattice resonance. Consequently, the beaming properties along x and y directions are drastically different. From the measurements, we obtain the M 2 value along both principal directions of the square lattice as a function of the pump fluence. Our work provides the first detailed analysis of the beam quality in plasmonic lattice lasers and reveals the underlying physical origin of the observed strong polarization dependent asymmetry of the lasing signal.

Activating and modulating ferroelectric and optical properties in La/Nd co-doped SrTiO3 ceramics

Defect-dipole and defect-clusters provide a novel paradigm to realize unprecedented dielectric behavior along with ultralow dielectric loss, in any ordinary dielectric material. In the present work, with the help of the La/Nd co-doped SrTiO3 (STO) system, it has been shown that the type, nature, and localization of these defect dipoles and clusters play a significant role in controlling the dielectric behavior. Polycrystalline ceramic samples of La0.1Sr0.9−xNdxTiO3 (x = 0.05, 0.07, 0.09, 0.11) are synthesized by mechanical alloying followed by high temperature solid-state reaction techniques. Investigations of structural and microstructural properties are carried out by using the X-ray diffraction technique and scanning electron microscopy, respectively. The dielectric and electrical parameters are studied in a frequency ranging from 1 kHz to 1 MHz and the temperature ranging from 30 °C to 450 °C. The results demonstrate that all the synthesized samples exhibit single-phase perovskite structure with Pm3̅m space group. Though STO displays quantum paraelectric behavior, intriguingly, all the La/Nd doped STO samples exhibit ferroelectric behavior with the dielectric maximum increasing with the increase in the doping concentration. The superior dielectric behavior in the doped samples is ascribed to the suppression of grain boundary conductivity due to the formation of a double Schottky barrier (due to VSr′′/Vo••) and enhancement of grain conductivity due to localized transport involving defect dipoles/clusters within the grain. Interestingly, the presence of VSr′′andVo•• has been supported by the photoluminescence analysis. Nevertheless, La/Nd doping results in a systematic reduction in the band gap.

Transport Modeling of Locally Photogenerated Excitons in Halide Perovskites.

Excitons have fundamental impacts on optoelectronic properties of semiconductors. Halide perovskites, with long carrier lifetimes and ionic crystal structures, may support highly mobile excitons because the dipolar nature of excitons suppresses phonon scattering. Inspired by recent experimental progress, we perform device modeling to rigorously analyze exciton formation and transport in methylammonium lead triiodide under local photoexcitation by using a finite element method. Mobile excitons, coexisting with free carriers, can dominate photocurrent generation at low temperatures. The simulation results are in excellent agreement with the experimentally observed strong temperature and gate dependence of carrier diffusion. This work signifies that efficient exciton transport can substantially influence charge transport in the family of perovskite materials.

Excitons in Bilayer MoS_{2} Displaying a Colossal Electric Field Splitting and Tunable Magnetic Response.

van der Waals heterostructures composed of transition metal dichalcogenide monolayers (TMDCs) are characterized by their truly rich excitonic properties which are determined by their structural, geometric, and electronic properties: In contrast to pure monolayers, electrons and holes can be hosted in different materials, resulting in highly tunable dipolar many-particle complexes. However, for genuine spatially indirect excitons, the dipolar nature is usually accompanied by a notable quenching of the exciton oscillator strength. Via electric and magnetic field dependent measurements, we demonstrate that a slightly biased pristine bilayer MoS_{2} hosts strongly dipolar excitons, which preserve a strong oscillator strength. We scrutinize their giant dipole moment, and shed further light on their orbital and valley physics via bias-dependent magnetic field measurements.

Mechanism of chain formation under shearing forces in magneto-rheological fluids

The present article focuses on the basic physics of structure formation chain formation and chain dynamics that make variation in viscoelastic properties of magnetorheological (MR) fluids. The formation and deformation of chain like structures in MR fluids at room temperature has been studied under the application of shearing force and externally applied magnetic field. The morphological investigation of MR fluid particles has been studied using SEM. A rheomicroscopy set-up was used to record the in-situ videos under magnetic field’s influence and a sequence of images were taken whose analysis has been performed using ImageJ. The plot of chain length versus shear rate at constant magnetic fields reveals the competitive nature of dipole–dipole interactions and shear forces acting simultaneously.

A novel Mn4+-activated layered oxide-fluoride perovskite-type KNaMoO2F4 red phosphor for wide gamut warm white light-emitting diode backlights.

Mn4+-activated oxide-fluoride phosphors are attractive for application in a wide range of solid-state lighting devices because of their distinct red emission at about 630 nm and the abundant storage of Mn ions. However, the zero-phonon line (ZPL) of Mn4+ ions is too weak to be detected in most host materials due to the magnetic dipole nature. In this article, we introduce a co-precipitation method for synthesizing a Mn4+-doped oxyfluoride perovskite KNaMoO2F4 phosphor containing [MoO2F4]2- building units. The electron paramagnetic resonance (EPR) spectra are consistent with the presence of a MnF62- species at g = 1.991. The KNaMoO2F4:0.01Mn4+ phosphor exhibits strong absorption under blue light and an internal quantum yield (IQE) of 65.8%. Attributed to the distorted octahedral environment of the Mn4+ ions, visible ZPL emission was detected at 625 nm. Based on theoretical calculations, the Mn4+ ions in the KNaMoO2F4 host exist in a strong crystal field with a high Dq/B value of ∼3.86. A series of photoluminescence-dependent low-temperature spectra indicates that the Mn4+ emissive state experiences weak electron-phonon interactions upon calculating the Huang-Rhys factor. Benefiting from the ZPL, a warm white-light-emitting diode is achieved using YAG:Ce3+ and KNaMoO2F4:Mn4+ as color converters, in which the color rendering index was Ra = 83.5 and CCT = 4490 K.

Switching resonance character within merocyanine stacks and its impact on excited-state dynamics

Summary In this study, the optical properties and excited-state dynamics of the unique self-assembled donor-acceptor (DA) merocyanine dye stacks from dimer up to octamer, prepared via dipole-dipole interactions, are reported in terms of coherent exciton dynamics and formation of an excimer-like state. Our findings are based on the steady-state absorption/emission, time-resolved fluorescence, and transient absorption (anisotropy) measurements, including wavepacket analysis and quantum mechanical calculations. Coherent exciton of torsional motions-restricted dye stacks rapidly localizes into the weakly emissive excimer-like state, by shortening the inter-moiety distance and changing the bond-length alternation pattern. The inner merocyanine moiety, having two neighboring units, has a reversed resonance character (non-polar (N) Z) in the ground state. This difference has led to two conclusions: (1) tetramers and octamers exhibit different features of excimer-like state than the dimer, and (2) octamers exhibit slower localization dynamics due to the enhanced homogeneity (six inner-moieties) compared with tetramers (two inner moieties).