Screening Radius Research Articles

The interaction between charged dust particles in a plasma

A solution to the Poisson-Boltzmann equation for a cloud of charges surrounding two charged dust particles, considered as Debye atoms forming a Debye molecule, is studied by numerical methods. It is demonstrated that attractive forces between the particles arise when two conditions are satisfied. First, the Debye screening radius, corresponding to the electron density at a half average spacing between particles, must be equal to approximately half of this distance. In this case, the attraction arises at a distance equal approximately to the average spacing between particles. Second, charges of one sign must be concentrated predominantly on the particles. Should the particles possess only a small fraction of charges of one sign, they will repulse at any distance. Estimates of the electrostatic pressure and surface tension in a gas of dust particles are obtained.

Coulomb glass in the restricted random phase approximation

A three-dimensional model of N/2 electrons localized on N randomly distributed donor sites of density n and with the acceptor charge uniformly smeared on these sites, − e/2 on each, has been considered in the restricted random phase approximation (RRPA) which uses the set of 3 N Fourier components of the local charge density as the independent collective variables. The energy e( T) per site and the density of one-site excitation energy (DOSE) g( ε) are shown to be, respectively, in excellent quantitative and in good qualitative agreement with the Monte Carlo simulation data in the whole temperature region 0.1< T<100, where these simulations were performed ( e 2 n 1/3/ k B being the temperature scale). The pair correlator for the one-site energies g( ε,± ε, r) is found to have the slow decoupling law ∼(±1/ r) for T≲1 and r⪢ r d ( r d , Debye screening radius). The status of the commonly accepted asymptotic g( ε)∼( ε− μ) d−1 ( d and μ being, respectively, the spatial dimension and the Fermi energy) is discussed. The “deduction” of this asymptotic is shown to be based on the strong and questionable conjecture about decoupling of correlations between one-site excitation energies in the vicinity of μ.

The interaction between charged dust particles calculated in Cassini coordinates

The Poisson-Boltzmann equation for two charged dust particles surrounded by a cloud of charged plasma was numerically solved using the Cassini coordinates. The force of the electric field acting on each particle was determined by integrating the field pressure over the particle surface. It is shown that the dust particles can exhibit attraction at distances on the order of the Debye screening radius and the average spacing between particles. The attraction drops sharply if the particle charge is significantly smaller than the charge of surrounding plasma species.

Potential of a dust grain in a nitrogen plasma with a condensed disperse phase at room and cryogenic temperatures

The first numerical study is presented of the self-consistent potential of a dust grain in a nitrogen plasma with a condensed disperse phase at room and cryogenic temperatures and at high gas pressures for which the electron and ion transport in the plasma can be described in the hydrodynamic approximation. It is shown that the potential of the dust grain is described with good accuracy by the Debye potential, in which case, however, the screening radius turns out to be larger than the electron Debye radius. The difference between the radii is especially large in a plasma with high ionization rates (about 1016–1018 cm−3 s−1) at room temperature. It is found that, in a certain range of the parameters of a nitrogen dusty plasma, the parameter describing the interaction between the grains exceeds the critical value above which one would expect the formation of plasma-dust structures such as Coulomb crystals. For a plasma at cryogenic temperature (T=77 K), this range is significantly wider.

Critical behavior of dilute electrolyte solutions

A theory of the critical behavior of a dilute ionic solution is constructed. An expression for the susceptibility in a wide temperature range is obtained. It is shown that ionic solutions belong to the universality class of the Ising model. The Ginzburg parameter of the ionic solutions decreases with the increase of the solvent concentration. In the general case, the critical exponent of susceptibility nonmonotonically depends on the temperature in the crossover region from the Ising-like to the mean-field behavior. In the vicinity of the transition point, the Debye-Huckel screening radius is proportional to the correlation length. As T→Tc, the screening radius tends to infinity and the screening disappears. The voltage between the two phases of the ionic solution is proportional to the order parameter and changes as |T/Tc−1|β in the vicinity of the phase transition point.

Universal and specific contributions in the density-like functionals: Application to transition metals

We present an approach for obtaining generating functionals for density-functional-like theory, which takes into account the structure of electronic levels near Fermi surface and density variations at distances exceeding the screening radius in metals. Materials-specific information is contained mainly in these structure-dependent terms, while other terms depend mainly on the local density. We used proposed method to study the electronic structure of ferromagnetic Fe and Ni and obtain reasonable agreement with previous local density calculations and experiment.

A correction factor to the screening radius for atomic interactions involving hydrogen and its application in direct recoil spectrometry

The screening function of the atomic interaction potential in low-energy ion scattering and recoiling was investigated for collisions involving hydrogen. Time-of-flight direct recoil spectrometry (TOF-DRS) and the M arlowe computer code were used to derive a correction factor, with explicit atomic-number dependence, to the screening radius specific to X–H interactions, where X represents any other atom. The improved screening radius was tested in the simulation of TOF spectra. The observed results displayed very good agreement with experimental data. The application of this correction factor in computer simulation studies of ion-surface interactions involving H should improve the exactness of the calculations and lead to more accurate differential interaction cross-sections.

Method for determining the stoichiometric composition of a mercury cadmium telluride solid solution from capacitance-voltage characteristics

A procedure is proposed for determining the stoichiometric composition of an intrinsic semiconductor Hg1−xCdxTe, relying upon the field effect in an electrolyte. An original comparative analysis of experimental capacitance-voltage characteristics and those calculated in terms of a quantum description of the space charge region provides the x value in the surface layer of the semiconductor at a depth comparable with the Debye screening radius. The determined stoichiometric compositions are presented for four Hg1−xCdxTe samples (x=0.205, 0.245, 0.290, and 0.330).

Effect of Screening on Thermonuclear Fusion in Stellar and Laboratory Plasmas

The fusion-enhancement factor due to screening in the solar plasma is calculated. We use the finite-temperature Green's function method, and a self-consistent mean field approximation. We reduce this to one-center problems, because in the collision of two fusing ions, the turning point where tunneling may occur lies far inside the screening radius. The numerical results given by this method indicate that screening may be slightly weaker than that obtained in the most recent previous calculations.

Electrical conductivity of fully ionized nonideal plasma with screened interaction between charges

The Boltzmann equation is solved, and the electrical conductivity of fully ionized nonideal plasma with screened interaction between particles is determined. For the screening radius, the interpolation relation between the Debye and average interparticle radii is used. The correlation of the Spitzer factor γE and Coulomb logarithm Λ with the nonideality parameter Γ is established. It is shown that different methods of elimination of distant collisions, based on the restriction of the transport scattering cross sections of charged particles and of their interaction potential, yield close values of the electrical conductivity of plasma

Negative electrostatic contribution to the bending rigidity of charged membranes and polyelectrolytes screened by multivalent counterions.

Bending rigidity of a charged membrane or polyelectrolyte screened by monovalent counterions is known to be enhanced by electrostatic effects. We show that in the case of screening by multivalent counterions the electrostatic effects reduce the bending rigidity. This inversion of the sign of the electrostatic contribution is related to the formation of two-dimensional strongly correlated liquids (SCL) of counterions at the charged surface due to strong lateral repulsion between them. When a membrane or a polyelectrolyte is bent, SCL is compressed on one side and stretched on the other so that thermodynamic properties of SCL contribute to the bending rigidity. Thermodynamic properties of SCL are similar to those of Wigner crystal and are anomalous in the sense that the pressure, compressibility and screening radius of SCL are negative. This brings about substantial negative correction to the bending rigidity. For the case of DNA this effect qualitatively agrees with experiment.

Hadron diffractive processes: the structure of soft pomeron and colour screening

On the basis of the experimental data on diffractive processes in πp, pp and p¯p collisions at intermediate, moderately high and high energies, we restore the scattering amplitude related to the t-channel exchange by vacuum quantum numbers by taking account of the diffractive s-channel rescatterings. At intermediate and moderately high energies, the t-channel exchange amplitude turns, with a good accuracy, into an effective pomeron which renders the results of the additive quark model. At superhigh energies the scattering amplitude provides a Froissart-type behaviour, with an asymptotic universality of cross sections such as σtot πp/σtot pp→ 1 at s→∞. The quark structure of hadrons being taken into account at the level of constituent quarks, the cross sections of pion and proton (antiproton) in the impact parameter space of quarks, σπ(r 1⊥, r 2⊥; s) and σp(r 1⊥, r 2⊥, r 3⊥; s), are found as functions of s. These cross sections implicate the phenomenon of colour screening: they tend to zero at |r i⊥−r k⊥|→ 0. The effective colour screening radius for pion (proton) is found for different s. The predictions for the diffractive cross sections at superhigh energies are presented.

On the Coulomb corrections to the total cross section of the interaction of the π+π− atom with ordinary atoms at high energy

The size of $\pi^+\pi^-$ atom in the low lying states is considerably smaller than the radius of atomic screening. Due to that we can neglect this screening calculating the contribution of multi-photon exchanges. We obtain the analytic formula for Coulomb corrections which works with a very good accuracy for the ground state of $\pi^+\pi^-$ atom.

On the effect of dislocation arrays on the superconducting transition temperature in HTSC

It is shown that arrays of edge dislocations with parallel Burgers vectors in the slip plane can lead to significant local changes in the transition temperature Tc of the deformed crystals of high-temperature superconductors. These changes are due to the redistribution of free charge carriers in the elastic strain fields of the ionic crystal lattice and a strong nonmonotonic dependence of Tc on the concentration of charge carriers if the characteristic length of dislocation arrays is much larger than the coherence length and screening radius.

Capture of carriers by screened charged centres and low-temperature shallow-impurity electric field breakdown in semiconductors

Free-carrier capture by a screened Coulomb potential in a semiconductor is considered. It is established that with decreasing screening radius the capture cross section decreases drastically, and it goes to zero when . On the basis of this result, a new mechanism of shallow-impurity electric field breakdown in semiconductors is suggested.

Reliable rectifiers and photovoltaic converters for high levels of ionizing irradiation

Nonlinear charge carrier transport has been investigated for the metal-intrinsic semiconductor-metal (M-i-M) and heterojunction of two intrinsic semiconductor (i-i) structures. It is shown that if the film thickness is of the order of the Debye screening radius, the current—voltage characteristics of these structures become comparable to those observed for the usual junctions at the base of doped semiconductors. The possibility of solid-state electronic devices at the base of M-i-M and i-i thin film structures is demonstrated. For intrinsic semiconductors, using semiconductors of the In 2Te 3 type, which cannot be effectively doped, but possess extremely high radiation stability, permits one to create a family of electronic devices for application under conditions of very high levels of ionizing irradiation.

Dielectric relaxation with dipolar screening

The phenomenon of dipolar screening does not appear to have received any attention in the past and yet we are showing that it is capable of explaining some forms of dielectric response to which no other evident explanation exists. A theory of dipolar screening is presented and it is shown that relatively "dense" systems give complete screening so that neighbouring dipoles do not "see" one another, while in more dilute systems many dipoles fall within a screening radius R/sub s/ of any one dipole. The energetically favoured configuration is for dipoles within R/sub s/ to adopt antiparallel orientations and the entire system "seizes up" in an "antiferroelectric domain" thereby reducing the number of dipoles which can be re-oriented at finite frequencies.

The Thomas–Fermi Type Screening of the Crystal Field Multipole Moments

Using a nonintegral expansion method of screened potentials about a displaced center (bya) the intrinsic crystal-field terms generated by the point charge, dipole, and quadrupole moments of a ligand have been quantitatively estimated. The calculation has been performed within the Thomas–Fermi model for the screening radius 1/λ ≥a/3. In contrast to an almost total attenuation of the monopole component (of no contribution to the crystal-field splitting) the screening efficiency for higher crystal-field terms regularly drops. The screening factor for the fourth-order terms does not exceed 0.5 and that for the sixth-order, 0.3. In the case of the second-order crystal-field terms a particular situation is observed. Their screening factor for the point-charge potential reaches 0.6 for λa= 3 but contributions generated by the dipole and quadrupole components are several times enhanced. This fact may explain some interpretation difficulties occurring often in the case of the second-order parameters and concerning both their magnitude and sign.

Anderson localization in quantum high magnetic field

1. I N T R O D U C T I O N New interest to investigations of transverse and longitudinal diffusion in quantum high magnetic field H is connected with a progress in understanding of these phenomena, achieved recently. In contrast to tile first theoretical calculations for conductivity tensor components many inodem authors are trying to take into account a quasi one-dimensional character of electron dynamic, that leads to the Anderson localization (AL) of electrons in the random potential of chaotically distributed charged impurities in ultra-quantum limit (UQL). In 1978 Abrikosov and Ryzlddn tried to summarize diagrams of higher order in the perturbation theory, but they succeeded only in the case of short range impurity potential, that really did not lead to AL [1]. Therefore their result practically coincide with previous received from kinetic equation. For the most interesting case of charged impurities, that have a long range Coulomb potential, they had to use only a scaling hypothesis. Murzin [2] and Poliakov [3] following Dreizin and Dykhne [4] had taken into account tile correlation in scattering acts on charged impurities because of and probability of an electron returns to the same crystal regions. Later Murzin combined this idea with conception of AL. In his model AL could be destroyed by a transverse displacement of these localized states because of electric drifting in magnetic and electric fields crossed to each other [5]. Within the framework of the oneelectron model in the case of a classical screening (CS) he received the following behaviors of dependencies for longitudinal and transverse components of conductivity tensor: o,, QcH -6 and o~, ocH s~. In our previous paper [6] we had taken into account, that the opposite case of quantum screening (QS) occupied a significant part of the UQL region. For QS case, where a wave length of Fermi electrons XF became more, than a radius of screening r,. our calculations gave quite different dependencies: r ocH 2 and oxx ocH ~ Their comparison with the experimental data for n-htSb had shown that for a such material it was impossible to observe CS and QS regions separatly, because an extent of the UQL region was limited by magnetic freeze out effect, that is really a ease of metal-dielectric or the Mort transition (MT).

Self-organization of precipitates during Ostwald ripening

Spontaneous pattern formation of precipitates is analysed using the diffusion interaction between precipitates. A theoretical model for studying the instability of the Ostwald ripening process in a material near the critical radius of precipitates is proposed and results of computer simulations of Ostwald ripening of a finite ensemble of precipitates are presented. It is shown that, in contrast to homogeneous systems, in this case the Ostwald ripening process can lead to a spatial structure of the precipitates due to the diffusion interaction and self-organisation process in space. The wavelength structure is obtained depending on initial conditions (the density and the initial critical radius of precipitates). It is proportional to the screening radius of the precipitates.