Self-consistent theory of screening in a two dimensional electron gas under strong magnetic field

The dielectric response of a two dimensional electron gas under a strong transverse magnetic field is obtained within a self-consistent procedure in which the broadening of Landau levels due to collisional damping from the impurities both determines and is determined by the static dielectric function of the system. The dielectric function is evaluated in random phase approximation with the impurity scattering treated in a self-consistent Born approximation. Explicit results are presented for the zero temperature, extreme quantum limit. It is found that this “no parameter” theory is in good qualitative agreement with experimental results for the broadening as extracted from magnetotransport data.     

Dielectric relaxation spectrum of water studied by the site—site generalized Langevin/modified mode-coupling theory

The dielectric relaxation spectrum of water is calculated from the site-site generalized Langevin/modified mode-coupling theory. The main part of the relaxation follows the Debye-type function, and a small deviation from the Debye relaxation is found on the high-frequency side. This tendency is consistent with recent experiments, although the absolute relaxation time does not agree with the experimental value quantitatively. The time development of the longitudinal polarization function resembles the dielectric part of the memory function, and we consider that this is because the dielectric friction dominates the collective reorientation of the dipole moment of water. We performed calculations with different dielectric constants using the reference interaction-site model integral equation, and found that the large gap between the time scales of the dielectric relaxation and the longitudinal polarization relaxation causes the Debye-type dielectric relaxation in our theory when the dielectric friction is dominant in the friction on the collective reorientation of the dipole moment. Namely, the longitudinal polarization relaxation is fast enough to be considered as a white noise to the dielectric relaxation process, so that the relaxation becomes a Markov process. The large gap between the two relaxation times originates from a large local field correction owing to the large dielectric constant of water. It is also suggested that the deviation from the Debye relaxation at the high-frequency side is the manifestation of the slow memory caused by the long-time part of the longitudinal polarization relaxation in the low-wavenumber region.     

Microscopic calculation of the constitutive relations

Homogenization theory is used to calculate the macroscopic dielectric constant from the quantum microscopic dielectric function in a periodic medium. The method can be used to calculate any macroscopic constitutive relation, but it is illustrated here for the case of electrodynamics of matter. The so-called cell problem of homogenization theory is solved and an explicit expression is given for the macroscopic dielectric constant in a form akin to the Clausius-Mossotti or Lorentz-Lorenz relation. The validity of this expression is checked by showing that the standard formula is recovered for cubic materials and that the average of the microscopic energy density is the macroscopic one. Finally, the general expression is applied to Bloch eigenstates.     

Lindhard dielectric function in the relaxation-time approximation and generalized linear response theory

Within a generalized linear response theory, an expression for the dielectric function is derived which allows to include the effect of collisions. Former attempts to include collisions into the Lindhard dielectric function by a relaxation time are discussed and systematic improvements are outlined.     

Analytical inversion of dielectric matrix of electron gas with one-dimensional inhomogeneity

In the framework of classical electrodynamics by analytical inversion of dielectric matrix simple expressions are derived for macroscopic dielectric function and function of energy losses. The electron density of systems under study is arbitrary function of one coordinate. Fourth scattering of incident electrons is treated. The theory is applicable to foils, surfaces and structures of one-dimensional periodicity. The model calculation is presented, where the importance of non-diagonal elements of dielectric matrix (local-field effects) is explicitly demonstrated.     

Van der Waals interactions in ionic and semiconductor solids

van der Waals (vdW) energy corrected density-functional theory [Phys. Rev. Lett. 102, 073005 (2009)] is applied to study the cohesive properties of ionic and semiconductor solids (C, Si, Ge, GaAs, NaCl, and MgO). The required polarizability and dispersion coefficients are calculated using the dielectric function obtained from time-dependent density-functional theory. Coefficients for "atoms in the solid" are then calculated from the Hirshfeld partitioning of the electron density. It is shown that the Clausius-Mossotti equation that relates the polarizability and the dielectric function is accurate even for covalently-bonded semiconductors. We find an overall improvement in the cohesive properties of Si, Ge, GaAs, NaCl, and MgO, when vdW interactions are included on top of the Perdew-Burke-Ernzerhof or Heyd-Scuseria-Ernzerhof functionals. The relevance of our findings for other solids is discussed.     

Dielectric properties of paper as a function of of moisture content at 9 GHz

This letter gives values of the complex dielectric constant of a good quality paper as a function of the moisture content at 9 GHz. The experimental results are interpreted using Weiner's theory for dielectric mixtures.     

电介质损耗理论

本文用全Wigner函数导出含有两个参数的跃迁几率分布函数,解释了Jonscher的电介质损耗经验公式,改进了Ngai电介质损耗理论。 关键词：     

Improving accuracy by subpixel smoothing in the finite-difference time domain

Finite-difference time-domain (FDTD) methods suffer from reduced accuracy when modeling discontinuous dielectric materials, due to the inhererent discretization (pixelization). We show that accuracy can be significantly improved by using a subpixel smoothing of the dielectric function, but only if the smoothing scheme is properly designed. We develop such a scheme based on a simple criterion taken from perturbation theory and compare it with other published FDTD smoothing methods. In addition to consistently achieving the smallest errors, our scheme is the only one that attains quadratic convergence with resolution for arbitrarily sloped interfaces. Finally, we discuss additional difficulties that arise for sharp dielectric corners.     

Towards a theory of molecular forces between deformed media

A macroscopic theory for the molecular or Casimir interaction of dielectric materials with arbitrarily shaped surfaces is developed. The interaction is generated by the quantum and thermal fluctuations of the electromagnetic field which depend on the dielectric function of the materials. Using a path integral approach for the electromagnetic gauge field, we derive an effective Gaussian action which can be used to compute the force between the objects. No assumptions about the independence of the shape and material dependent contributions to the interaction are made. In the limiting case of flat surfaces our approach yields a simple and compact derivation of the Lifshitz theory for molecular forces [Sov. Phys. JETP 2 (1956) 73]. For ideal metals with arbitrarily deformed surfaces the effective action can be calculated explicitly. For the general case of deformed dielectric materials the applicability of perturbation theory and numerical techniques to the evaluation of the force from the effective action is discussed.     

Cu、Zn掺杂对AlSb电子结构和光学性质影响

运用密度泛函平面波赝势方法和广义梯度近似,对替代式掺杂Cu和Zn的闪锌矿AlSb的超晶胞晶体结构、电子结构和光学性质进行了计算。分析了其电子态分布和结构的关系,给出了掺杂前后AlSb体系的复介电常数和复折射函数。结果表明,掺有Cu和Zn的AlSb晶体空穴密度增大,会明显提高材料的电导率;两种掺杂体系光学带隙均变窄;通过分析掺杂前后AlSb晶体的复介电常数和复折射函数,解释了体系的发光机制。     

氢离子在固体表面掠角散射与能量损失的数值模拟

利用介电响应理论和镜像反射模型对氢离子在固体表面掠角散射和能量损失进行了数值模拟．离子在表面散射时同时受到表面上原子的库仑排斥作用和表面电子气的动力学相互作用,后者是表面电子受运动的正离子扰动所产生,用线性介电响应理论来确定．在高速和低速情况下,分别采用仅与频率有关的局域介电函数和局域场修正介电函数来确定表面电子气产生的动力学相互作用力．计算结果与实验结果作了比较．发现入射速度很低时能量损失随入射角度变化不太明显,而当速度很高时能量损失随入射角度的变大而有所增加. 关键词：     

Extended Mermin‐like Dielectric Function for a Two‐Component Plasma

The Mermin dielectric function is extended by including energy conservation. Within the framework of the relaxation time ansatz, the Zubarev approach to linear response theory is used which allows to incorporate the exact Hamiltonian dynamics of the relevant degrees of freedom. Analytical expressions for the dielectric function in the entire (k, w)‐plane are given for a two‐component plasma.     

Quantum Thermal Transport through Extremely Cold Dielectric Chains

In the framework of Green＇s function theory out of equilibrium, a Landauer-Buttiker （LB） formula for thermal conductance is derived. A simplified model for describing extremely cold dielectric chains is proposed for the first time. Further we apply the present LB formula for studying thermal conductance at low-lying modes, emerging in dielectric atom chains. We find that quantum thermal conductance undergoes an anomalous transition due to new quasiparticle excitations, resulting from nonlinear atom-atom interactions. This theoretical prediction is in excellent agreement with a high-accuracy measurement to thermal conductance quantum.     

Dielectric function of the QCD vacuum

It is shown that the inverse of the ghost form factor in the Hamilton approach to Yang-Mills theory in Coulomb gauge can be interpreted as the color dielectric function of the QCD vacuum. Furthermore, the horizon condition to the ghost form factor implies that in the infrared the QCD vacuum is a perfect color diaelectric medium and therefore a dual superconductor. The dielectric function is explicitly calculated within a previously developed variational approach, using a specific ansatz for the vacuum wave functional.     

Dielectric function and plasma resonances of small metal particles

Using the simple model of electrons in a box, a dielectric function is derived which should be appropriate for small metal particles. This dielectric function is used to examine quantum size effects in the optical absorption spectra. For very small particles of uniform size and shape, the plasma resonance absorption should shift and broaden and should show fine structure corresponding to transitions between discrete conduction band energy levels. The size dependence of the shift and broadening was measured and found to be in quantitative agreement with theory.     

Dielectric critical behaviour at a metal-insulator transition under lattice compression

We study dielectric critical behaviour around a continuous metal-insulator transition in crystalline Cesium Iodide induced by changing the lattice parameter. The ab initio calculations of band structure and various quantities related to the dielectric response are performed in the transition region, within the local density approximation of the density functional theory. These calculations allow us to establish the power-law singularities of various quantities on two sides of the transition. The exponents obtained here are mean-field like due to the approximation in which interactions and disorder are treated. The critical behaviour is discussed by applying the scaling principle to the wavevector and frequency dependent dielectric function. We further investigate the effect of dielectric anomalies on optical properties by calculating the reflectance around transition region taking the ionic contribution to the dielectric function also into account. We find that the reflectance as a function of frequency shows very different kind of behaviour on both sides of the metal-insulator transition.     

Electronic Energy Loss and Straggling of Protons in Metals

By making use of the linear-response dielectric theory and local electron density approximation, we calculate the electronic stopping cross section and energy straggling. of protons in metals. The correlation and exchange interaction of electron gas in metals is taken into consideration by introducing a local-field-correction function.in the dielectric function. The theoretical results are compared with experimental and empirical data, as well as with other previous theoretical results.     

Millimeter-wave scattering from neutral and charged water droplets

We investigated 94 GHz millimeter-wave (MMW) scattering from neutral and charged water mist produced in the laboratory with an ultrasonic atomizer. Diffusion charging of the mist was accomplished with a negative ion generator (NIG). We observed increased forward- and backscattering of MMW from charged mist, as compared to MMW scattering from an uncharged mist. In order to interpret the experimental results, we developed a model based on classical electrodynamics theory of scattering from a dielectric sphere with diffusion-deposited mobile surface charge. In this approach, scattering and extinction cross-sections are calculated for a charged Rayleigh particle with effective dielectric constant consisting of the volume dielectric function of the neutral sphere and surface dielectric function due to the oscillation of the surface charge in the presence of applied electric field. For small droplets with radius smaller than 100 nm, this model predicts increased MMW scattering from charged mist, which is qualitatively consistent with the experimental observations. The objective of this work is to develop indirect remote sensing of radioactive gases via their charging action on atmospheric humid air.     

Second-order theory of the dielectric response function of the electron gas

Using the Green function formalism an expression for the dielectric response function (or density-density function) is derived which is of second order with respect to the Coulomb interaction and applies for arbitrary wave vector and frequency. The employed procedure is somehow lengthy but quite clear from the mathematical point of view. Decoupling methods for Green functions are not used. The theory contains the well-known expressions of the HFA, RPA and the first-order local field theory. In addition to this all four-particle processes (two electrons and two holes) are taken into account and represented in a closed formula, which is the four-particle analog to the Lindhard function. As a first application the plasmon damping is investigated.