Long-range Coulomb Forces Research Articles

Inclusion of the long-range proton-proton Coulomb force in the three-nucleon scattering Faddeev calculations

Inclusion of the long-range proton-proton Coulomb force in the three-nucleon scattering Faddeev calculations

The electron affinity of rubidium: a state selective measurement

Negative ions, which are formed when an electron is attached to a neutral system, are unique quantum systems. The lack of a long-range Coulomb force causes the inter-electronic interactions to become relatively more important. As a consequence, the independent particle model, which adequately describes atomic structure under normal conditions, breaks down. The alkali negative ions, with a closed valence s-shell, are among the simplest anionic systems. Hence, they can favorably be used to benchmark atomic theory. In this work, we have determined the electron affinity of 85Rb by measuring the relative partial photodetachment cross section of the negative ion, leaving the residual atom in the 5p 2P3/2 excited state. Resonance ionization spectroscopy allows for state selectivity and the ability to measure the Wigner s-wave threshold onset of the photodetachment process. The electron affinity of 85Rb was determined to be 485.887(6) meV.

Thickness-dependent variations of atomic vibration, band-edge excitonic emission, and valleytronic response in layered Mo0.55W0.45S2 ternary compounds

Two-dimensional (2D) van der Waals transition metal dichalcogenides (TMDs) are highly attractive due to their novel phenomena and potential device applications, but most of the studies are focused on binary TMDs except a few reports on ternary TMDs. Here, we report thickness-dependent mono-to-multi-layer transition behaviors of mechanically-exfoliated ternary TMD Mo0.55W0.45S2. Dependences of Raman modes and their peak intervals on thickness (d) are divided into three regions (1.5 ≤ d ≤ 9.2, 9.2 < d ≤ 34, and > 34 nm), mostly resulting from the increase of van der Waals force and long-range Coulomb force in interlayer interactions at larger d. Photoluminescence (PL) peak and its intensity/full width at half maximum show similar three-region behaviors, which are associated with direct-to-indirect-bandgap transition as d increases. In particular, critical changes in the Raman scattering and PL occur at d = 9.2 nm (8–13 layers), meaning a 2D-to-3D transition. The effect of the valley polarization is observed up to d = 8.1 nm (7–11 layers), resulting from random mixing-induced suppression of the inversion symmetry in the multilayer. These results suggest that the critical layer number for the 2D-to-3D dimensional crossover in ternary Mo0.55W0.45S2 is considerably larger than in binary TMDs, thereby exhibiting the direct-bandgap nature in an extended range of layer number, more useful for their optoelectronic device applications.

High pressure phase boundaries of AgNbO3

The external pressure is one of the essential parameters for regulating the structure and energy conversion properties of antiferroelectric AgNbO3. For pure AgNbO3, however, there has been still a blank of its real lattice structure under the stress field. Here, high-pressure lattice structures and phase transitions of AgNbO3 have been explored by spectroscopic experiments and theoretical models. A successive phase transition process from Pbcm to C2221 to P21 has been observed at the pressure range of 0–30 GPa, associated with displacive-type characterized by soft-mode kinetics. Note that the paraelectric phase cannot be achieved under high-pressure at room temperature. Significantly, the competition of long-range Coulomb force, short-range interatomic interaction, and covalent interaction in AgNbO3 lattice were demonstrated under the stress field. The present work can provide fundamental guidelines to reveal the high-pressure phase transitions of AgNbO3, which will open up possibilities for the designing device with functional properties at extremes.

Coulomb distorted plane wave-Volkov ansatz for strong-field ionization

In the strong-field ionization of atomic and molecular systems, the photoelectron is exposed to the long-range Coulomb force which is neglected in the standard theories based on the strong-field approximation (SFA). We introduce an ansatz which takes into account the Coulomb effects and at the same time is as simple as the standard SFA. Our Coulomb distorted plane wave-Volkov approximation provides analytical expressions for the relevant matrix elements. We also present a generalization of this approximation taking into account first-order term of an expansion in the atomic potential. Similarly as in the standard improved SFA, this generalized approximation describes well the rescattering plateau and the cutoff observed in the photoelectron spectra. Our new approximation is illustrated with numerical examples of strong-field ionization of the hydrogen atom exposed to linearly and circularly polarized laser pulses. The spectra obtained are slightly flatten in comparison with the SFA spectra and this effect is stronger for shorter laser wavelengths.

Electron-phonon interaction and phonon frequencies in two-dimensional doped semiconductors

Electron-phonon interaction and phonon frequencies of doped polar semiconductors are sensitive to long-range Coulomb forces and can be strongly affected by the screening effects of free carriers, the latter changing significantly when approaching the two-dimensional limit. We tackle this problem within a linear-response dielectric-matrix formalism, where the screening effects can be properly taken into account by generalized effective charge functions and the inverse scalar dielectric function, allowing for controlled approximations in relevant limits. We propose complementary computational methods to evaluate from first principles both effective charges---encompassing all multipolar components beyond dynamical dipoles and quadrupoles---and the static dielectric function of doped two-dimensional semiconductors and provide analytical expressions for the long-range part of the dynamical matrix and the electron-phonon interaction in the long-wavelength limit. As a representative example, we apply our approach to study the impact of doping in disproportionated graphene, showing that optical Fr\"ohlich and acoustic piezoelectric couplings, as well as the slope of optical longitudinal modes, are strongly reduced, with a potential impact on the electronic/intrinsic scattering rates and related transport properties.

Pressure-induced dynamically stable HeK2S under moderate conditions

It is accepted that helium as one of inert gases is hard to combine due to its stable closed shell electron configuration. With the maturity of first principles calculations, helides are not rare under high pressures, which fuels the enthusiasm for finding helium-based compounds at moderate conditions. Here, we performed a first principle exploration on the crystal structures and the corresponding electronic properties of HeK2S at 0–100 GPa. Two phases with Fm-3m and Cmma space groups are predicted, dynamically stable at ambient pressure and high pressure. As concerns the structures, K2S acts as a precompressor to stabilize the helium sublattice. Our work reveals that no chemical bond is formed when He atom insertion, which is stabilized by long-range Coulomb interaction force.

Electrospun membranes filtering 100nm particles from air flow by means of the van der Waals and Coulomb forces.

Nonwoven fibrous filter membranes are widely used in filtration because of their low cost. They are less effective in intercepting airborne particles of the order of 100nm, which is of the SARS-CoV-2 (COVID-19) virus's size. Many diseases, including COVID-19, predominantly spread by droplets released by breathing, coughing, sneezing, or medical procedures. It was shown that the smallest droplets can evaporate in air before settling, thus, making viruses airborne and easily penetrating even the best masks and filters. As a result, air-filtering membranes, which are capable of effective interception of ∼100nm nanoparticles are highly desirable. A traditional way to improve filtration efficiency by overlapping several layers of nonwoven fabrics increases the required pressure drop, and thus, should be avoided as much as possible. Here, we propose and demonstrate an innovative approach to enhance performance of filtration membranes based on (i) a dramatic reduction in the fiber size, and (ii) metal coating of the fibers. The first component of this approach allows one to incorporate a novel physical mechanism of filtration, the short-range van der Waals forces, whereas the second one adds the long-range electric Coulomb forces if the oncoming nanoparticles are pre-charged and the metal-plated membrane grounded. In the present work, the ∼100nm aluminum nanoparticles are filtered as a model of commensurate airborne single COVID-19 viruses, and Platinum is used as the sputter-coated material for the fiber coating. The resulting filtration efficiency enhanced by the electric Coulomb forces alone is increased by the factor of 1.77, while the filtration efficiency additionally facilitated by the van der Waals forces increased by the factor of 2.44. In comparison to the filter membranes with ∼500nm fibers without the electric forces involved, the van-der-Waals-electric filter membrane with fibers ∼90nm is 2.24 1.77=3.96 times more effective. The quality factor of a membrane which combines the van der Waals and Coulomb forces is 10.6 psi-1, which is almost three times that of a comparable membrane without the electric Coulomb force (with only van der Waals forces being used).

Coulomb, Yukawa, and Hooke’s Oscillations

Oscillations due to three different forces in three areas of physics: electrostatic, nuclear, and mechanics, are analyzed. The electrostatic long-range Coulomb force has a different character than the nucleonic short-range Yukawa force. Both are different from the linear Hooke’s force. The equation of motion of each case is solved applying a Computer Algebra System (CAS). It is shown that these oscillations have similarities and differences. Phase diagrams of all three cases are compared.

Phase boundary of gas hydrates in single and mixed electrolyte solutions: Using a novel unified equation of state

The phase boundary of gas hydrates is key to flow assurance, energy recovery, and hydrate-based technologies. In this work, a new thermodynamic model has been proposed for calculating the phase boundary of gas hydrates based on a unified equation of state (EoS) for the non-hydrate phases and the van der Waals-Platteeuw (vdW-P) model for the hydrate phase. A modified Peng-Robinson EoS is employed to describe the interactions between water, gas, and uncharged ions, combining with a simplified explicit mean spherical approximation (MSA) term for the long-range Coulombic forces and the Born terms for the discharging-charging process of ions. A new set of reference properties have been applied and the Kihara parameters in the vdW-P model are optimized by fitting against the measured phase boundary data of hydrates formed in the pure water. The newly developed model has been validated with 734 measured phase boundary data points of pure CH4 and binary CH4-C2H6 and CH4-CO2 hydrates formed in single- and mixed-NaCl, KCl, MgCl2, and CaCl2 solutions as well as in the pure water. It is found that this model is capable of predicting the phase boundary of CH4 hydrates formed in the 1–1 electrolyte solutions (NaCl-KCl) with the average absolute relative deviation (AARD) of 3.7%. The AARD of CH4 hydrates formed in the 2–1 electrolyte solutions (MgCl2-CaCl2) is 4.2%, which is greater than that for the 1–1 electrolytes. This is acceptable given the fact that none of the ion-associated parameters have been optimized in this work. The calculated phase boundary of pure CH4 hydrate formed in mixed-electrolyte solutions deviates from the measured ones only by 2.8%. The AARD of the binary hydrates (CH4-CO2 and CH4-C2H6) formed in single- and mixed-electrolyte solutions is 3.5%. This model can also be reduced to calculate the hydrate phase boundary in pure water. The AARD of the CH4-CO2 hydrates formed in pure water is determined as 3.0%. The overall AARD of these 734 data points predicted by this newly developed model is 3.4%, which proves the capability of the newly developed model in predicting the phase boundary of hydrates in multi-component systems. It is also presented that this unified EoS is reliable to determine the gas solubility in aqueous phase with and without electrolytes.

Extreme near-field heat transfer between gold surfaces

Extreme near-field heat transfer between metallic surfaces is a subject of debate as the state-of-the-art theory and experiments are in disagreement on the energy carriers driving heat transport. In an effort to elucidate the physics of extreme near-field heat transfer between metallic surfaces, this paper presents a comprehensive model combining radiation, acoustic phonon, and electron transport across sub-10-nm vacuum gaps. The results obtained for gold surfaces show that in the absence of bias voltage, acoustic phonon transport is dominant for vacuum gaps smaller than $\ensuremath{\sim}2$ nm. The application of a bias voltage significantly affects the dominant energy carriers as it increases the phonon contribution mediated by the long-range Coulomb force and the electron contribution due to a reduced potential barrier. For a bias voltage of 0.6 V, acoustic phonon transport becomes dominant at a vacuum gap of 5 nm, whereas electron tunneling dominates at sub-nm vacuum gaps. The comparison of the theory against experimental data from the literature suggests that well-controlled measurements between metallic surfaces are needed to quantify the contributions of acoustic phonon and electron as a function of the bias voltage.

Magnetoplasmon resonance in two-dimensional fluctuating superconductors

We develop a theory of the magnetoplasmon resonance (MPR) in two-dimensional superconductors in the fluctuating regime, where the temperature is slightly above the critical temperature of the superconducting transition. In this regime, unpaired electrons and fluctuating Cooper pairs coexist in the system and interact with each other via long-range Coulomb forces, forming a Bose–Fermi mixture. The sample is considered to be under the influence of an external time-dependent electromagnetic field with a frequency in sub-terahertz range and a permanent magnetic field. It is shown that the MPR of the system is strongly modified in the presence of superconducting fluctuations in the vicinity of the superconducting transition. In particular, the fluctuating Cooper pairs dramatically change the broadening of the MPR, which is reflected in the optical response of the system.

Metastable piezoelectric group-IV monochalcogenide monolayers with a buckled honeycomb structure

Twelve two-dimensional group-IV monochalcogenide monolayers (SiS, SiSe, SiTe, GeS, GeSe, GeTe, SnS, SnSe, SnTe, PbS, PbSe, and PbTe) with a buckled honeycomb atomistic structure--belonging to symmetry group P3m1--and an out-of-plane intrinsic electric polarization are shown to be metastable by three independendent methods. First, we uncover a coordination-preserving structural transformation from the low-buckled honeycomb structure onto the lower-energy Pnm2$_1$ (or Pmmn for PbS, PbSe, and PbTe) phase to estimate {\em energy barriers} $E_B$ that must be overcome during such structural transformation. Using the curvature of the local minima and $E_B$ as inputs to Kramers escape formula, large escape times are found, implying the structural metastability of the buckled honeycomb phase (nevertheless, and with the exception of PbS and PbSe, these phases display escape times ranging from 700 years to multiple times the age of the universe, and can be considered "stable" for practical purposes only in that relative sense). The second demonstration is provided by phonon dispersion relations that include the effect of long-range Coulomb forces and display no negative vibrational modes. The third and final demonstration of structural metastability is furnished by room-temperature {\em ab initio} molecular dynamics for selected compounds. The magnitude of the electronic band gap evolves with chemical composition. Different from other binary two-dimensional compounds such as transition metal dichalcogenide monolayers and hexagonal boron nitride monolayers which only develop an in-plane piezoelectric response, the twelve group-IV monochalcogenide monolayers with a buckled honeycomb structure also display out-of-plane piezoelectric properties.

Tunneling conductance of long-range Coulomb interacting Luttinger liquid

The theoretical model of the short-range interacting Luttinger liquid predicts a power-law scaling of the density of states and the momentum distribution function around the Fermi surface, which can be readily tested through tunneling experiments. However, some physical systems have long-range interaction, most notably the Coulomb interaction, leading to significantly different behaviors from the short-range interacting system. In this paper, we revisit the tunneling theory for the one-dimensional electrons interacting via the long-range Coulomb force. We show that even though in a small dynamic range of temperature and bias voltage, the tunneling conductance may appear to have a power-law decay similar to short-range interacting systems, the effective exponent is scale-dependent and slowly increases with decreasing energy. This factor may lead to the sample-to-sample variation in the measured tunneling exponents. We also discuss the crossover to a free Fermi gas at high energy and the effect of the finite size. Our work demonstrates that experimental tunneling measurements in one-dimensional electron systems should be interpreted with great caution when the system is a Coulomb Luttinger liquid.

Survey of nuclear pasta in the intermediate-density regime: Structure functions for neutrino scattering

Background: Nuclear pasta matter, emerging due to the competition between the long-range Coulomb force and the short-range strong force, is believed to be present in astrophysical scenarios, such as neutron stars and core-collapse supernovae. Its structure can have a high impact, e.g., on neutrino transport or the tidal deformability of neutron stars.Purpose: We investigate the impact of nuclear pasta on neutrino interactions and compare the results to uniform matter.Method: We calculate the elastic and inelastic static structure factors for nuclear pasta matter, using density functional theory (DFT), which contain the main nuclear input for neutrino scattering.Results: Each pasta structure leaves a unique imprint in the elastic structure factor and it is largely enhanced. The inelastic structure factors are very similar for all configurations.Conclusion: Nuclear pasta has a noticeable impact on neutrino neutral-current scattering opacities. While for inelastic reactions the cross section is reduced, the elastic coherent scattering increases dramatically. The effect can be of importance for the cooling of neutron stars as well as for core-collapse supernova models.

Interplay between collective modes in hybrid electron-gas–superconductor structures

We study hybridization of collective plasmon and Carlson-Goldman-Artemenko-Volkov modes in a hybrid system, consisting of a two-dimensional layers of electron gas in the normal state and superconductor, coupled by long-range Coulomb forces. The interaction between these collective modes is not possible in a regular single-layer two-dimensional system since they exist in non-overlapping domains of dimensionless parameter $\omega\tau$, where $\omega$ is the external electromagnetic field frequency and $\tau$ is electron scattering time. Thus, in a single-layer structure, these modes are mutually exclusive. However, the coupling may become possible in a hybrid system consisting of two separated in space materials with different properties, in particular, the electron scattering time. We investigate the electromagnetic power absorption by the hybrid system and reveal the conditions necessary for the hybridization of collective modes.

One-dimensional few-electron effective Wigner crystal in quantum and classical regimes

A system of confined charged electrons interacting via the long-range Coulomb force can form a Wigner crystal due to their mutual repulsion. This happens when the potential energy of the system dominates over its kinetic energy, i.e., at low temperatures for a classical system and at low densities for a quantum one. At $T=0$, the system is governed by quantum mechanics, and hence, the spatial density peaks associated with crystalline charge localization are sharpened for a lower average density. Conversely, in the classical limit of high temperatures, the crystalline spatial density peaks are suppressed (recovered) at a lower (higher) average density. In this paper, we study those two limits separately using an exact diagonalization of small one-dimensional (1D) systems containing few ($<10$) electrons and propose an approximate method to connect them into a unified effective phase diagram for Wigner few-electron crystallization. The result is a qualitative quantum-classical crossover phase diagram of an effective 1D Wigner crystal. We show that the spatial density peaks associated with the quasi-crystallization should be experimentally observable in a few-electron 1D system. We find that the effective crystalline structure slowly disappears with both the crossover average density and crossover temperature for crystallization decreasing with increasing particle number, consistent with the absence of any true long-range 1D order. In fact, one peculiar aspect of the effective finite-size nature of 1D Wigner crystallization we find is that even a short-range interaction would lead to a finite-size 1D crystal, except that the crystalline order vanishes much faster with increasing system size in the short-range interacting system compared with the long-range interacting one.

Survey of nuclear pasta in the intermediate-density regime: Shapes and energies

Background: Nuclear pasta, emerging due to the competition between the long-range Coulomb force and the short-range strong force, is believed to be present in astrophysical scenarios, such as neutron stars and core-collapse supernovae. Its structure can have a high impact e.g. on neutrino transport or the tidal deformability of neutron stars. Purpose: We study several possible pasta configurations, all of them minimal surface configurations, which are expected to appear in the mid-density regime of nuclear pasta, i.e. around 40% of the nuclear saturation density. In particular we are interested in the energy spectrum for different pasta configurations considered. Method: Employing the density functional theory (DFT) approach, we calculate the binding energy of the different configurations for three values of the proton content XP = 1/10, 1/3 and 1/2, by optimizing their periodic length. We study finite temperature effects and the impact of electron screening. Results: Nuclear pasta lowers the energy significantly compared to uniform matter, especially for $X_P \geq 1/3$. However, the different configurations have very similar binding energies. For large proton content, $X_P \geq 1/3$, the pasta configurations are very stable, for lower proton content temperatures of a few MeV are enough for the transition to uniform matter. Electron screening has a small influence on the binding energy of nuclear pasta, but increases its periodic length. Conclusion: Nuclear pasta in the mid-density regime lowers the energy of the matter for all proton fractions under study. It can survive even large temperatures of several MeV. Since various configurations have very similar energy, it is to expected that many configurations can coexist simultaneously already at small temperatures.

High pressure structural phase transition and elastic properties of ZnSexTe1−x semiconducting compounds

This paper discusses the high pressure-dependent crystal structure phase transformation and elastic behavior of ZnSe[Formula: see text]Te[Formula: see text] (x = 0.0, 0.2, 0.55, 0.81, 0.93 and 1.0) by speculating effective interionic interaction potential (EIoIP), that contains long-range type Coulomb force, short-range overlap repulsion of the Hafemeister and Flygare types and the van der Waals (vdW) interaction. The assessed values of structural phase transition pressure and the considerable volume discontinuity associated with the pressure–volume phase diagram support the structural phase transformation from zinc blende (B3) type to rock-salt (B1) type crystal structure. The equation of state curves (relationship between V(p)/V(0) and pressure in the pressure–volume phase diagram) for both the zinc blende (B3) and rock-salt (B1) structures is in reasonably good agreement with that of experimental observations. Moreover, systematic variations of the second-order elastic constants (SOEC) with pressure have been found to follow systematic trends showed by the other systems with B3 type to B1 type pressure-dependent structural phase transition.

Electrification in granular gases leads to constrained fractal growth

The empirical observation of aggregation of dielectric particles under the influence of electrostatic forces lies at the origin of the theory of electricity. The growth of clusters formed of small grains underpins a range of phenomena from the early stages of planetesimal formation to aerosols. However, the collective effects of Coulomb forces on the nonequilibrium dynamics and aggregation process in a granular gas – a model representative of the above physical processes – have so far evaded theoretical scrutiny. Here, we establish a hydrodynamic description of aggregating granular gases that exchange charges upon collisions and interact via the long-ranged Coulomb forces. We analytically derive the governing equations for the evolution of granular temperature, charge variance, and number density for homogeneous and quasi-monodisperse aggregation. We find that, once the aggregates are formed, the granular temperature of the cluster population, the charge variance of the cluster population and the number density of the cluster population evolve in such a way that their non-dimensional combination obeys a physical constraint of nearly constant dimensionless ratio of characteristic electrostatic to kinetic energy. This constraint on the collective evolution of charged clusters is confirmed both by our theory and our detailed molecular dynamics simulations. The inhomogeneous aggregation of monomers and clusters in their mutual electrostatic field proceeds in a fractal manner. Our theoretical framework is extendable to more precise charge exchange mechanisms, a current focus of extensive experimentation. Furthermore, it illustrates the collective role of long-ranged interactions in dissipative gases and can lead to novel designing principles in particulate systems.