Range Coulomb Interaction Research Articles

Rapidly rotating boson molecules with long- or short-range repulsion: An exact diagonalization study

The Hamiltonian for a small number $N\ensuremath{\leqslant}11$ of bosons in a rapidly rotating harmonic trap, interacting via a short range (contact potential) or a long range (Coulomb) interaction, is studied via an exact diagonalization in the lowest Landau level. Our analysis shows that, for both low and high fractional fillings, the bosons localize and form rotating boson molecules (RBMs) consisting of concentric polygonal rings. Focusing on systems with the number of trapped atoms sufficiently large to form multiring bosonic molecules, we find that, as a function of the rotational frequency and regardless of the type of repulsive interaction, the ground-state angular momenta grow in specific steps that coincide with the number of localized bosons on each concentric ring. Comparison of the conditional probability distributions (CPDs) for both interactions suggests that the degree of crystalline correlations appears to depend more on the fractional filling $\ensuremath{\nu}$ than on the range of the interaction. The RBMs behave as nonrigid rotors, i.e., the concentric rings rotate independently of each other. At filling fractions $\ensuremath{\nu}<1∕2$, we observe well developed crystallinity in the CPDs (two-point correlation functions). For larger filling fractions $\ensuremath{\nu}>1∕2$, observation of similar molecular patterns requires consideration of even higher-order correlation functions.

Coulomb Interactions and Nanoscale Electronic Inhomogeneities in Manganites

We study electronic inhomogeneities in manganites using simulations on a microscopic model with Coulomb interactions amongst two electronic fluids-one localized (polaronic), the other extended-and dopant ions. The long range Coulomb interactions frustrate phase separation induced by the large on site repulsion between the fluids. A single phase ensues which is inhomogeneous at a nanoscale, but homogeneous on mesoscales, with many features that agree with experiments. This, we argue, is the origin of nanoscale inhomogeneities in manganites, rather than phase competition or disorder effects.

Influence of Young-type interference on the forward-backward asymmetry in electron emission fromH2in collisions with80−MeVbare C ions

We use the forward-backward angular asymmetry in the electron emission cross sections in fast ion impact ionization of H2 as a probe of the inversion symmetric coherence in homonuclear diatomic molecules. The electron energy dependence of the asymmetry parameter for H2 exhibits oscillatory structure due to Young-type interference in contrast to atomic targets such as He. The asymmetry parameter technique provides a selfnormalized method to reveal the interference oscillation independent of theoretical models and complementary measurements on atomic H target. DOI: 10.1103/PhysRevA.74.060701 PACS numbers: 34.50.Fa, 34.50.Gb Angular distribution of various types of radiations particles and photons is known to be quite sensitive to various effects associated with different physical processes in atomic, nuclear, plasma physics and other branches of physics. In fast ion-atom ionization, the long range Coulomb interaction of the final state electrons with the target and the projectile ions influences the evolution of the electron wave function and thereby the angular distribution of electron emission. Such two-center effect is known to cause a large forward-backward asymmetry 1‐4 in the electron emission spectrum. The electron emission spectrum from the simplest diatomic molecule H2 manifests yet another important aspect of interference 5 in ion-atom ionization besides the wellknown mechanisms such as soft collision, two-center effect and binary encounter 1‐4,6‐8. Since the two indistinguishable H atoms in the H2 molecule may be considered as the coherent emission sources of phase coupled electrons in a large impact parameter collision, their contributions add coherently and an interference effect should be observed. Therefore, the electron emission from H2 may be viewed as a natural coherent system which is similar to Young’s double slit interference phenomenon 5. We demonstrate here that the additional mechanism of Young-type interference plays a major role in the angular asymmetry of electron double differential cross section DDCS and asymmetry parameter itself would be a sensitive test to study the interference for a diatomic molecular target. Following the initial theoretical studies on the interference effect in electron scattering 9 and photoionization 5, very recently the evidence of Young-type interference was found in the fast-ion collisions with H2 10‐12. Ideally one would have expected an oscillation in the DDCS spectrum due to interference. But a steep fall of the DDCS by about four or five orders of magnitude see below does not allow one to observe the oscillation directly. The oscillations, thereby, were observed in the DDCS ratios H2-to-2H which was explained due to the interference. However, the experiments using H are rare due to the experimental constraint and oscillations in the DDCS ratios were observed 4,12 in such experiment with H. Theoretical DDCS for atomic, or effective atomic H have also been employed 10,11 in the absence of an atomic H target. In such cases, the shapes of the oscillations are sensitive to the atomic parameters such as the effective atomic number Zeff which is model dependent. So far oscillations have not been observed based on the H2 DDCS data only. In this work we present a method based on the analysis of the asymmetry parameter which is independent of normalization procedures and permits therefore to observe the interference effect directly in the H2 data only. By eliminating the need for the data on atomic H is an important step forward in the study of this

Influence of atomistic physics on electro-osmotic flow: An analysis based on density functional theory

Molecular density profiles and charge distributions determined by density functional theory (DFT) are used in conjunction with the continuum Navier-Stokes equations to compute electro-osmotic flows in nanoscale channels. The ion species of the electrolyte are represented as centrally charged hard spheres, and the solvent is treated as a dense fluid of neutral hard spheres having a uniform dielectric constant. The model explicitly accounts for Lennard-Jones interactions among fluid and wall molecules, hard sphere repulsions, and short range electrical interactions, as well as long range Coulombic interactions. Only the last of these interactions is included in classical Poisson-Boltzmann (PB) modeling of the electric field. Although the proposed DFT approach is quite general, the sample calculations presented here are limited to symmetric monovalent electrolytes. For a prescribed surface charge, this DFT model predicts larger counterion concentrations near charged channel walls, relative to classical PB modeling, and hence smaller concentrations in the channel center. This shifting of counterions toward the walls reduces the effective thickness of the Debye layer and reduces electro-osmotic velocities as compared to classical PB modeling. Zeta potentials and fluid speeds computed by the DFT model are as much as two or three times smaller than corresponding PB results. This disparity generally increases with increasing electrolyte concentration, increasing surface charge density and decreasing channel width. The DFT results are found to be comparable to those obtained by molecular dynamics simulation, but require considerably less computing time.

QUANTUM 1/f EFFECT BASED ON QUANTUM INFORMATION THEORY

The Quantum Information Theory Approach (QIT) explains for the first time the apparent lack of unitarity caused by the entropy increase in the Quantum 1/f Effect (Q1/fE). This allows for a deeper understanding of the quantum 1/f effect, showing no resultant entropy increase and therefore no violation of unitarity in the quantum-mechanical dynamical evolution. This new interpretation involves the von Neumann Quantum Entropy, including the negative conditional entropy concept for quantum entangled states introduced by QIT. The Q1/fE was applied to many high-tech systems, in particular to ultra small electronic devices in nanotechnology. The present paper explains how the additional entropy implied by the observed 1/f noise arises in spite of the entropy-conserving evolution of the system. On this basis, a derivation of the conventional and coherent quantum 1/f effect is given. The latter is derived from a non-relativistic form of the branch-point propagator derived by excluding the long range Coulomb interaction from the interaction hamiltonian. The paper concludes with examples of practical applications in various devices and systems, allowing for a new characterization of high technology.

Dielectric Response of the Charge Ordered State in Quasi-One-Dimensional Organic Conductors

We present a survey of the recent experimental results which provide the evidence for the formation in quasi-one-dimensional (Q1D) conductors of a charge ordered (CO) state corresponding to an electronic 4 k F charge density wave. The main attention is paid to the study of the dielectric response of Q1D organic compounds of the family of (TMTTF) 2 X salts for which a divergence of the dielectric permittivity and of the relaxation time at the critical transition temperature into the CO state are found. Effects of pressure and deuteration on this transition and also the role of anions in the formation of the CO state are studied. On the basis of these results and existing theoretical approaches we suggest a phenomelogical explanation of the sequence of ground states developed in these compounds with decreasing temperature. The driven force for the formation of the CO state originates from strong electron correlation effects associated with long range Coulomb interactions. The stability of the CO state in (TMTTF) 2 X compounds is expected to be provided by a shift of anion chains as a whole. A short comparison between peculiarities in the dielectric response of the CO state formation in Q1D and recently found in Q2D compounds will be given.

Pressure dependence of elastic properties of ZnX (X = Se,S and Te): Role of charge transfer

An effective interaction potential (EIOP) is developed to invoke the pressure induced phase transition from zinc blende (B3) to rocksalt (B1) structure and anharmonic properties in ZnX (X = Se, S, Te) semiconductors. The effective interaction potential incorporates the long range Coulomb interaction, van der Waals interaction and short-range repulsive interaction up to second neighbour ions within the Hafemeister and Flygare approach as well as the charge transfer effects caused by the electron-shell deformation of the overlapping ions. The van der Waals coefficients are computed by the Slater Kirkwood variation method as a first step. Later on, we evaluate volume collapse, second order and third order elastic constants with pressure pointing to the systematic trends in all compounds of zinc blende structure and their thermal properties such as force constant, Gruneisen parameter, compressibility, Debye temperature etc. The vast volume discontinuity in pressure-volume (PV) phase diagram identifies the structural phase transition from zinc blende (B3) to rock salt (B1) structure and is consistent with those revealed from earlier reports.

4KFCDW induced by long range Coulomb interactions

By method of dielectric spectroscopy we have obtained experimental data concerning the 4k F charge density wave (CDW) associated with the charge ordering (CO) state of Wigner type in (TMTTF) 2 X conductors. A divergence of the relaxation time was found at the critical transition temperature T CO into the CO state. Below T CO a low frequency shoulder appears in the frequency dependence of the imaginary part of the dielectric permittivity. Under a moderate pressure, the peak in the real part of the dielectric permittivity, corresponding to the transition into the CO state, shifts to low temperature and broadens. The substitution of hydrogen by deuterium in TMTTF molecules results in an increase of T CO (isotopic effect). The results obtained confirm the ferroelectric character of the CO state; they also favour long range Coulomb interactions as the main driven force for the formation of this state.

Ion Transport through Membrane-Spanning Nanopores Studied by Molecular Dynamics Simulations and Continuum Electrostatics Calculations

Narrow hydrophobic regions are a common feature of biological channels, with possible roles in ion-channel gating. We study the principles that govern ion transport through narrow hydrophobic membrane pores by molecular dynamics simulation of model membranes formed of hexagonally packed carbon nanotubes. We focus on the factors that determine the energetics of ion translocation through such nonpolar nanopores and compare the resulting free-energy barriers for pores with different diameters corresponding to the gating regions in closed and open forms of potassium channels. Our model system also allows us to compare the results from molecular dynamics simulations directly to continuum electrostatics calculations. Both simulations and continuum calculations show that subnanometer wide pores pose a huge free-energy barrier for ions, but a small increase in the pore diameter to ∼1 nm nearly eliminates that barrier. We also find that in those wider channels the ion mobility is comparable to that in the bulk phase. By calculating local electrostatic potentials, we show that the long range Coulomb interactions of ions are strongly screened in the wide water-filled channels. Whereas continuum calculations capture the overall energetics reasonably well, the local water structure, which is not accounted for in this model, leads to interesting effects such as the preference of hydrated ions to move along the pore wall rather than through the center of the pore.

A particle–particle particle-multigrid method for long-range interactions in molecular simulations

A fast method of order O ( N ) is proposed to calculate interaction energies and forces in molecular systems with open boundaries, exerted by long range Coulomb interactions. The method consists of a fast multigrid Poisson solver for the far field smooth part of the potential and a particle–particle based method for the near field contribution. Boundary conditions are calculated with a multipole expansion method. Test cases are performed for the performance of the method.

Stress anisotropy induced by periodic boundary conditions

Finite size effects due to periodic boundary conditions are investigated using computer simulations in the canonical ensemble. We study liquids with densities corresponding to typical liquid coexistence densities, and temperatures between the triple and critical points. The components of the pressure tensor are computed in order to analyze the finite size effects arising from the size and geometry of the simulation box. Two different box geometries are considered: cubic and parallelepiped. As expected the pressure tensor is isotropic in cubic boxes, but it becomes anisotropic for small noncubic boxes. We argue this is the origin of the anomalous behavior observed recently in the computation of the surface tension of liquid-vapor interfaces. Otherwise, we find that the bulk pressure is sensitive to the box geometry when small simulation boxes are considered. These observations are general and independent of the model liquid considered. We report results for liquids interacting through short range forces, square well and Lennard-Jones, and also long range Coulombic interactions. The effect that small surface areas have on the surface tension is discussed, and some preliminary results at the liquid vapor-interface for the square well potential are given.

Formation of Strongly Coupled Plasmas from MultiComponent Ions in a Penning Trap

This report reviews the production of strongly-coupled, multi-component, non-neutral, highly-charged ion plasmas in a cryogenic Penning trap. A unique ion source–Penning trap system has been developed and used an Electron Beam Ion Trap-Source (EBIT-S), able to produce ions up to U92+, has been combined with a cold-bore Penning ion trap. The developed experimental techniques such as the ion production, extraction, bunching, multi-ion species trapping and storage (ions up to Th80+), detection, cooling, and imaging are presented. The produced mixed plasmas, consisting of several ion species [e.g. Be+, Xeq+ (charge q = 34 ... 44)], are cooled to a temperature of about 1 degree Kelvin and below. These low temperatures were obtained by applying a sypathetic cooling scheme, using laser cooled Be+ ions. The determination of the temperature and the density from the laser resonance width and the fluorescence imaging of the Be+ clouds respectively, yield a Coulomb coupling parameter for the xenon ion plasma of over 1000, large enough for crystallization. Crystallization can be achieved at these relatively high temperatures since the Coulomb coupling parameter scales with q2.Ion species with different mass to charge ratios centrifugally separate at low temperatures in the trap, and the plasma consists of concentric spheroidal shells of single component plasmas. But even in this case excellent thermal coupling between ion species takes place due to the long range Coulomb interactions. This is demonstrated by molecular dynamics simulations of the ion mixtures, which show ordered structures, indicating evidence for crystallization of the highly charged xenon ions.During the investigation of highly charged ion Coulomb crystallization in mixed strongly coupled plasmas, several enabling techniques were developed that are applicable to various areas of physics research Analogous thermodynamics (Coulomb matter) of white dwarf astrophysical plasmas can experimentally be investigated, high precision laser spectroscopy is made possible due to reduced Doppler broadening effects, cold ion sources can be developed and coherent quantum control experiments can be further explored.

X-ray spectrum of a pinned charge density wave

We calculate the X-ray diffraction spectrum produced by a pinned charge density wave (CDW). The signature of the presence of a CDW consists of two satellite peaks, asymmetric as a consequence of disorder. The shape and the intensity of these peaks are determined in the case of a collective weak pinning using the variational method. We predict divergent asymmetric peaks, revealing the presence of a Bragg glass phase. We deal also with the long range Coulomb interactions, concluding that both peak divergence and anisotropy are enhanced. Finally we discuss how to detect experimentally the Bragg glass phase in the view of the role played by the finite resolution of measurements.

Coherent approach to transport and noise in double-barrier resonant diodes

We implement a quantum approach which includes long range Coulomb interaction and investigate current voltage characteristics and shot noise in double-barrier resonant diodes. The theory applies to the region of low applied voltages up to the region of the current peak and considers the wide temperature range from zero to room temperature. The shape of the current voltage characteristic is well reproduced and we confirm that even in the presence of Coulomb interaction the shot noise can be suppressed with a Fano factor well below the value of 0.5. This feature can be an indication of coherent tunneling since the standard sequential tunneling predicts in general a Fano factor equal to or greater than the value 0.5. This giant suppression is a consequence of Pauli principle as well as long range Coulomb interaction. The theory generalizes previous findings and is compared with experiments.

Effects of transverse electron dispersion on photo-emission spectra of quasi-one-dimensional systems

The random phase approximation (RPA) spectral function of the one-dimensional electron band with the three-dimensional long range Coulomb interaction shows a broad feature which is spread on the scale of the plasmon energy and vanishes at the chemical potential. The fact that there are no quasi-particle $\delta$-peaks is the direct consequence of the acoustic nature of the collective plasmon mode. This behaviour of the spectral function is in the qualitative agreement with the angle resolved photo-emission spectra of some Bechgaard salts. In the present work we consider the modifications in the spectral function due to finite transverse electron dispersion. The transverse bandwidth is responsible for the appearance of an optical gap in the long wavelength plasmon mode. The plasmon dispersion of such kind introduces the quasi-particle $\delta$-peak into the spectral function at the chemical potential. The cross-over from the Fermi liquid to the non-Fermi liquid regime by decreasing the transverse bandwidth takes place through the decrease of the quasi-particle weight as the optical gap in the long wavelength plasmon mode is closing.

Electronic interactions and excitons in conducting polymers

Conducting polymers can be considered as one-dimensional semiconductors with features of strongly correlated electronic systems. We can distinguish a large distance motion, governed by long range Coulomb interactions, and intra-molecular electronic correlations. We exploit the dielectric screening to go beyond the single chain picture and to compare excitons for polymers in solutions and in films. Our approach allows to connect such different questions as shallow singlet and deep triplet excitons in phenylenes, A g – B u exciton levels crossing in polyenes, common 1/ N energy dependencies in oligomers. For the fundamental edge structure we describe the suppression of DOS singularity by the long range Coulomb interactions in final state of e–h pair.

Giant suppression of shot noise as signature of coherent transport in double barrier resonant diodes

Shot noise suppression in double barrier resonant tunnelling diodes with a Fano factor well below the value of 0.5 is theoretically predicted. This giant suppression is found to be a signature of the coherent transport regime and can occur near zero temperature as a consequence of the Pauli principle or above about 77 K as a consequence of long range Coulomb interaction. These predictions are validated by experimental data.

Dense plasma effects on nuclear reaction rates.

Plasma density effects can cause an exponential change in charged particle nuclear reaction rates important in stellar evolution. Reaction rates in dense plasma, with emphasis on quantum aspects, are examined here using path integral Monte Carlo calculations. Quantum mechanics causes a reduction in the many body enhancement of the reaction rate compared to the value for a classical system. This can be attributed to the "quantum smearing" of the short range Coulomb interaction resulting in reduced repulsion between the reacting pair and surrounding particles. Electron screening and ion exchange effects are also examined, with screening reducing and exchange slightly increasing the many body enhancement.

Spin transresistivity—a probe of the opposite-spin correlations in an electron system

We investigate the spin drag effect in spin polarized transport beyond the random phase approximation by considering an effective scattering potential that incorporates self-consistently the effects of the short range Coulomb interaction through momentum dependent local field corrections. We find that the first order many-body correction to the spin transresistivity is determined by the local field factor for opposite-spin correlations.

Electron spin operation by electric fields: spin dynamics and spin injection

Spin–orbit interaction couples electron spins to electric fields and allows electrical monitoring of electron spins and electrical detection of spin dynamics. Competing mechanisms of spin–orbit interaction are compared, and optimal conditions for the electric operation of electrons spins in a quantum well by a gate voltage are established. Electric spin injection into semiconductors is discussed with a special emphasis on the injection into ballistic microstructures. Dramatic effect of a long range Coulomb interaction on transport phenomena in space-quantized low-dimensional conductors is discussed in conclusion.