Dynamical exchange corrections to the dielectric function in a two-dimensional electron gas

The effect of dynamical exchange interactions on the dielectric function of a two-dimensional electron gas is studied using a variational approach. Exchange effects are introduced via the local-field correction. The variationally obtained local-field factor is compared to the earlier perturbative result to first order in the electron-electron interaction.     

Macroscopic local-field effects on photoabsorption processes

The influence of the local-field effect on the photoabsorption cross sections of the atoms which are embedded in the macroscopic medium has been studied by a set of alternative expressions in detail. Some notes on the validity of some different local-field models used to study the photoabsorption cross sections of atoms in condensed matter have been given for the first time. Our results indicate that the local fields can have substantial and different influence on the photoabsorption cross section of atoms in condensed matter for different models. Clausius-Mossotti model and Onsager model have proved to be more reasonable to describe the local field in gas, liquid, or even some simple solid, while Glauber-Lewenstein model probably is wrong in these conditions except for the ideal gas. A procedure which can avoid the errors introduced by Kramers-Kronig transformation has been implemented in this work. This procedure can guarantee that the theoretical studies on the local field effects will not be influenced by the integral instability of the Kramers-Kronig transformation.     

Dynamical correlations in the one-dimensional electron gas with short-range interactions

We study the dynamical correlation effects in a one-dimensional Fermion gas with repulsive delta-function interaction within the quantum version of the self-consistent field approximation of Singwi, Tosi, Land, and Sj?lander [Phys. Rev. 176, 589 (1968)]. The dynamic correlation effects are described by a frequency dependent local-field correction . There is a corresponding local-field factor for the spin-density correlations. We investigate the structure factors, spin-dependent pair-correlation functions, the frequency dependences of and , and the plasmon dispersion relation within this formalism. We compare our results with other theoretical approaches, in particular the static version of the self-consistent field approximation to highlight the importance of dynamical correlations. Received 11 December 1998 and Received in final form 25 April 1999     

Lattice dynamics of molybdenum and tungsten

Summary The lattice dynamics of molybdenum and tungsten has been re-examined within the framework of the transition metal model potential by incorporating the local-field correction to the dynamical matrix for phonon dispersion relation. It is observed that the local-field correction can be represented by an attractive short-range potential which tends to cancel or ?screen? the Born-Mayer repulsion. The numerical calculations for molybdenum and tungsten show that the local-field correction plays a significant role and leads to a better agreement between the theoretically computed phonon dispersion curves and the experimental data.     

Correlation effects in the one-dimensional Bose gas

We discuss interaction effects for the one-dimensional Bose gas with a repulsive delta-function interaction potential. We use the random-phase approximation and a finite local-field correction. Analytical results are given for the local-field correction, the pair-correlation function and the ground-state energy. The groundstate energy is found to be in much better agreement with the exact result than the ground-state energy calculated within the Bogoliubov approximation, where local-field corrections are neglected.     

A dense collection of two-level atoms embedded in a dielectric medium in a ring cavity

The hysteresis behavior of a dense collection of two-level atoms embedded in a linear dielectric medium in an optical cavity is investigated theoretically in terms of a parametric formulation method under the thin-sample approximation. The relation of the output intensity to the input intensity is obtained in an explicit formula. The numerical results show that the hysteresis behavior and the cavity transmission are different from those in vacuum because of the local-field enhancement and the local cooperative decay effect. Received: 27 June 2000 / Revised version: 11 September 2000 / Published online: 10 January 2001     

Effects of local fields on spontaneous emission in dielectric media

The local-field renormalization of the spontaneous emission rate in a dielectric is explicitly obtained from a fully microscopic quantum-electrodynamical, many-body derivation of Langevin-Bloch operator equations for two-level atoms embedded in an absorptive and dispersive, linear dielectric host. We find that the dielectric local-field enhancement of the spontaneous emission rate is smaller than indicated by previous studies.     

Instability of layered quantum liquids: 5. Collective modes at low density

We calculate the plasmon dispersion of electron superlattices by taking into account many-body effects via the local-field correction. For small electron density we find a weak roton structure in the dispersion of optical plasmons. Landau damping is strongly enhanced by many-body effects, especially for acoustical plasmons. We compare with experimental results of high-T _c superconductors. Some experiments are suggested.     

Local-field enhancement of spontaneous decay in nanosystems: some estimations for dielectric particles

Enhancement of the spontaneous decay rate due to local-field effects is estimated for a luminous dipole inside a small dielectric particle. To do this, we make use of an idea on multiplicativity of the local-field factor. Elongated particles are shown to be promising in respect of the local-field enhancement of the spontaneous emission. Computations are carried out within the framework of modern theory of the spontaneous decay of excited atoms in absorbing media for both the virtual-cavity and real-cavity models. Particular emphasis is placed on dielectric/semiconductor particles in the vicinity of the optical phonon frequencies. PACS 32.80.-t; 33.50.-j; 78.55.-m; 78.67.-nThis revised version was published in October 2004 with a new Figure 5.     

Many-body dipole-induced dipole model for electrorheological fluids

Theoretical investigations on electrorheological (ER) fluids usually rely on computer simulations. An initial approach for these studies would be the point-dipole (PD) approximation, which is known to err considerably when the particles approach and finally touch each other due to many-body and multipolar interactions. Thus various works have attempted to go beyond the PD model. Being beyond the PD model, previous attempts have been restricted to either local-field effects only or multipolar effects only, but not both. For instance, we recently proposed a dipole-induced-dipole (DID) model which is shown to be both more accurate than the PD model and easy to use. This work is necessary because the many-body (local-field) effect is included to put forth the many-body DID model. The results show that the multipolar interactions can indeed be dominant over the dipole interaction, while the local-field effect may yield a correction.     

Silver-island films probed by hyper-Rayleigh scattering and atomic force microscopy

Incoherent second-harmonic generation, or hyper-Rayleigh scattering (HRS), and atomic force microscopy (AFM) are proposed as a combined probe of nonlinear optical and structural properties of silver-island films. HRS and linear (Rayleigh) scattering indicatrices are measured. The correlation function, deduced from the HRS indicatrices and characterising spatial fluctuations of the total polarisation at second-harmonic frequency, has a length scale significantly larger than that of the correlation functions that are obtained from the AFM data and characterise spatial fluctuations of quadratic optical susceptibilities of the dipole and quadrupole types. This difference is interpreted as indicating that the HRS indicatrix shape is determined by the long-range fluctuations of the local-field factors. Received: 16 October 2001 / Revised version: 16 April 2002 / Published online: 6 June 2002     

强耦合简并电子气中离子阻止本领和能量离散的数值计算

利用局域场修正的介电函数,研究了注入离子在强耦合简并电子气中的阻止本领和能量离散。数值结果表明在低速和高r_s值情况下,局域场修正使得阻止本领和能量离散明显地增加。     

Inclusion of the exchange-correlation effects in Ab initio methods for calculating the plasmon dispersion and line width in metals

A self-consistent analog of the Hubbard local-field factor accounting for a real band structure of the metal under investigation is proposed for the calculation of the exchange-correlation corrections to the randomphase approximation. The plasmon energy and the plasmon line width for potassium are calculated as a function of the wave vector. The calculations are performed within the random-phase approximation and with corrections for the local field. It is shown that the results of the calculations are in good agreement with the experimental data. This indicates that, first, the corrections to the random-phase approximation should be taken into account for metals with a low electron density and, second, the local-field factor approximation is an appropriate approach.     

Instability of layered quantum liquids: 4. Intraplane and interplane correlations

We calculate the local-field correctionsG(q, q _z) f electron superlattices with interlayer distanced in order to describe many-body effects. A generalized Hubbard expression for the local-field correction is derived. The sum-rule version of the self-consistent approach for the local-field correction is developed and used to discuss the effects of exchange and correlation. The RPA-parameterr _s and the ratiod/a ^* determine the many-body effects.a ^* is the effective Bohr radius. The stability region for the Fermi liquid behavior of the layered electron gas is discussed: (i) forda ^* the critical RPA-parameterr _sc1 is determined by exchange andintraplane correlation effects, (ii) forda ^* withr _sc1 correlation effects are small and the instability point is mainly determined by exchange effects, (iii) forda ^* withr _sc<1 exchange andinterplane correlation effects are both important for the instability point. Our results are important for high-T _c superconductors, organic superconductors and semiconductor superlattices.     

The quantum yield of a metallic nanoantenna

The local-field factor and quantum yield of a metallic nanoantenna are studied to identify its enhancement of an emitter’s emission within the feed gap. For simplicity, a two-dimensional model, an Au nanoantenna with an emitter at the center, is studied. The electromagnetic field is solved by a set of surface integral equations. An incident plane wave irradiating the nanoantenna is modeled to simulate the excitation of the emitter by illuminating light, and the local-field factor is used to evaluate the amplification of the electric field in the feed gap of the metallic nanoantenna. Once the emitter becomes excited, a model of an electric dipole interacting with the nanoantenna is used for calculating the radiative and nonradiative powers to obtain the quantum yield of the excited emitter in the presence of the nanoantenna. The numerical results of quantum yield indicate that an Au nanoantenna acts as a low-pass filter for the emission of the emitter. Moreover, the smaller the feed gap, the larger the local-field factor but the less the quantum yield. PACS 78.67.-n; 33.80.-b; 33.50.-j; 42.30.-d; 42.50.Hz; 81.07.Pr     

Quasi-particle properties in a quasi-two-dimensional electron liquid

We consider the quasi-particle properties such as the effective mass and spin susceptibility of quasi-two-dimensional electron systems. The finite quantum well width effects are incorporated into the local-field factors that describe the charge and spin correlations. We employ the Fermi-hypernetted chain formalism in conjunction with fluctuation-dissipation theorem to obtain the local-field factors. Our results are in good agreement with recent experiments.      

稠密共振介质中近偶极-偶极相互作用的局域场效应

 为研究存在由近偶极-偶极相互作用诱导的局域场效应时超短强激光脉冲与稠密共振介质相互作用的特性,采用光与物质相互作用的半经典理论,建立了稠密二能级体系中考虑原子间近偶极-偶极相互作用的修正光学Bloch方程,并用四阶Runge-Kutta法数值求解了该方程。研究结果表明:局域场效应对稠密二能级体系中Bloch矢量的瞬态相干过程和稳态性质都具有强烈的调制作用。并由此提出了调控稳态粒子数布居的两种方案。     

Effective electron-electron interactions and magnetic phase transition in a two-dimensional electron liquid

We investigate the spin-dependent effective electron-electron interactions in a uniform system of two-dimensional electrons to understand the spontaneous magnetization expected to occur at very low density. For this purpose, we adopt the Kukkonen-Overhauser form for the effective interactions which are built by accurately determined local-field factors describing the charge and spin fluctuations. The critical behavior of the effective interaction for parallel spin electrons allows us to quantitatively locate the transition to the ferromagnetic state at r_s≈27. When the finite width effects are approximately taken into account the transition occurs at r_s≈30 in agreement with recent quantum Monte Carlo calculations.