Effect Of Local-field Correction Research Articles

Drag resistivity in bilayer-graphene/GaAs coupled layer system with the effect of local field corrections

Drag resistivity mediated by Coulomb interaction is a transport phenomenon in a specially separated bilayer systems. The drag resistivity is numerically analysed for both the n- and p-type charge carriers between the bilayer-graphene and a GaAs layer, with an insulating barrier by using random phase approximation (RPA). The RPA method does not include exchange and correlation effects, which are included by assuming the local field correction (LFC) in effective interactions. Because of the LFC effects, the drag resistivity is found enhanced compared to the measured results of RPA. The present bilayer system shows a comparison between effect of electron–electron (e–e) repulsive and electron–hole (e–h) attractive interactions in Boltzmann regime for low temperature limit. Different masses of electrons and holes in GaAs layer are analysed, and drag resistivity is increased on increasing the effective mass of the charge carriers. The dependency of drag resistivity on temperature, concentration, interlayer separation, width of the drag layer and dielectric constant of barrier shows a consistent behaviour.

Study of coulomb drag with the effect of local field correction and dielectric medium

We present a numerical calculation for the drag resistivity of charge carriers interaction in coupled layer system separated by a barrier. Analytical expressions of non-linear susceptibility function and effective interlayer Coulomb interaction have been shown for non homogeneous dielectric environment at low temperature and low frequency regime. The system is studied within the model of random phase approximation (RPA) and taking into account the static local field correction (LFC). We employ Hubbard approximations (HA) and self consistent STLS approximations based LFC for obtaining the results, where LFC includes the exchange and correlation effects. Exchange and correlation effects enhanced the drag resistivity and the net screening. Another important quantity is the local form factors (LFF), which is the function of the bare inter- and intra-layer potential of the dielectric media. LFF for a multi-layer system is derived from the Poisson equation solution.

Coulomb drag study in graphene/GaAs bilayer system with the effect of local field correction and dielectric medium

The drag resistivity is measured numerically for electron-electron (e-e) and electron-hole (e-h) coupled layer system composed of single layer graphene and two-dimensional (2D) GaAs layer separated by a barrier. The system is studied within the model of random phase approximation (RPA) and taking into account the static local field correction (LFC) and layer thickness effects in the Ballistic/Boltzmann regime. We have shown analytical expressions of non-linear susceptibility function and effective interlayer Coulomb interaction for non homogeneous dielectric environment at low temperature, high density and large interlayer separation limit. Exchange and correlation effects enhanced the drag resistivity by considering the static local field correction. Width of the layer and interlayer distance dependent local form factors (LFF) are obtained from the solution of the Poisson equation for a multi-layer dielectric medium. The effects of LFC and LFF are the function of bare inter- and intra-layer potential, which enhances the drag resistivity compare to simply measured RPA results. Enhanced drag resistivity also measured for e-h bilayer system where the hole layer is considered for 2D GaAs (drag layer), cause of larger effective mass of hole compare to the electron. Similarly, e-e and e-h bilayer system measured the enhanced drag resistivity due to LFC effects.

Local field correction effect on inelastic Coulomb scattering lifetime of two-dimensional quasiparticles at low temperatures

We have investigated the effect of local field correction on the inelastic Coulomb scattering lifetime of high mobility quasiparticles in a quantum layer at low temperatures. By replacing temperature-dependent dynamic dielectric function for the zero-temperature one in calculations, we have considered our improved zero-temperature STLS local field correction for low temperatures in lifetime calculations and compared the results with those obtained from the RPA and Hubbard approximation. It has been found that the quasiparticle lifetime decreases by including the STLS local field factor in all temperatures, energies and layer thicknesses.

Effect of local field correction in screening dependence of superconducting state parameters for Be90Al10 and Be70Al30 metallic glasses

AbstractThe superconducting state parameters (SSP) viz. electron–phonon coupling strength (λ), Coulomb pseudopotential (μ*), transition temperature (Tc), isotope effect exponent (α) and interaction strength (N0V) for two metallic glasses, i.e. Be90Al10 and Be70Al30, have been investigated by extending the BCS–Eliasberg–McMillan formalism for the metallic glass superconductors incorporating the effect of local field correction in dielectric screening functions which in turn become prominent in determining superconducting state parameters of the metallic glasses under consideration. We have employed eleven forms of dielectric screening functions – viz. Hartree, RPA, Modified Hubbard, Overhauser, Geldart–Vosko, Animalu, King–Cutler, SCS, Vashistha–Singwi, Ichimaru–Utsumi, and Farid et al. – in conjunction with Ashcroft's potential to predict superconducting state parameters. It is observed that the values of SSP are quite sensitive to the form of dielectric screening functions. In conclusion the present computed values of SSP for the RPA form of dielectric screening are in good agreement with the experimental values and other theoretical results for both glassy materials, which confirms the validity of the proposed formalism. (© 2005 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Issues Concerning the Calculation of the Optical Response of Semiconductors

We consider a number of issues crucial to the realistic calculation of the linear and nonlinear optical response of semiconductor surfaces, including problems related to unphysical, apparent divergences in the calculations, the strong sensitivity of the calculated response to wave function symmetry, the effect of local field corrections in supercell calculations, and new nonlinear optical phenomena related to coherent control.

Quantum theory of multiwave mixing with a local field correction

In this paper, we calculate the four coefficients for the quantum theory of multiwave mixing including a local-field correction resulting from dipole-dipole interactions. We make contact with the semiclassical calculations of probe absorption and four-wave-mixing coupling coefficients, and illustrate the effects of local field corrections on resonance-fluorescence and coupled-mode-fluorescence spectra. The method uses the hybrid quantum-Langevin-equation master-equation approach of An and Sargent.

Chain model of electrorheology

We develop a chain model of an electrorheological fluid in steady and oscillatory shear. This model is based on a balance of hydrodynamic and electrostatic forces and focuses on the mechanical stability of chains. With this model we compute the shape and orientation of an unconfined dipolar chain in steady shear as a function of the shear rate and electric field, and show that this leads to the expected shear-thinning viscosity. We then demonstrate that chains confined by electrodes are unstable in some Mason number regimes. The chain model is extended to the case of oscillatory shear by including a kinetic equation for the aggregation and fragmentation of chains. The resultant chain dynamics is found to be strongly nonlinear, as is the rheology. Finally, we consider the effect of local field corrections and long range interactions on the bare dipolar interaction force and derive a self-consistent pair interaction force that demonstrates that the maximum orientation of a chain in shear depends strongly on the dielectric contrast.

Laser Instabilities and Chaos in Inhomogeneously Broadened Dense Media

Abstract We study numerically the effects of local-field corrections originating from near dipole—dipole interactions on the dynamics of a single mode, inhomogeneously broadened laser. Our analysis is based on a set of generalized Maxwell–Bloch equations in which the inhomogeneous nature of gain broadening is accounted for by introducing two new dynamical variables and a single parameter that governs the extent of inhomogeneous broadening. Our results show that local-field effects occurring in a dense gain medium reduce the range of continuous wave operation and lead to instabilities and chaos at much lower pumping levels.

Collective modes in a quasi-one-dimensional, two-component electron liquid

Under favorable conditions, a new collective mode besides the usual plasmons may exist in degenerate electron-hole liquids. We calculate the dispersion and damping of this new mode (called the acoustic plasmon mode) in a quasi-one-dimensional, two-component electron liquid. We carry out our calculations first within the random-phase approximation, then include the effects of local-field corrections using a Hubbard-like approximation. The latter decreases the acoustic plasmon dispersion.

The Effect of Local Field Corrections on the Electrical Resistivity of Liquid Metals

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Effects of the dynamic Lorentz shift on four-wave parametric interactions in a strongly driven two-level system.

We calculate the effect of the local-field correction (LFC) on the local response at ${\mathrm{\ensuremath{\omega}}}_{\mathit{s}}$ and 2${\mathrm{\ensuremath{\omega}}}_{\mathit{p}}$-${\mathrm{\ensuremath{\omega}}}_{\mathit{s}}$ of a medium consisting of two-level systems when subject to a pump of arbitrary intensity at ${\mathrm{\ensuremath{\omega}}}_{\mathit{p}}$ and a weak probe at ${\mathrm{\ensuremath{\omega}}}_{\mathit{s}}$. The pump is considered strong if its reduced intensity I=${\mathrm{\ensuremath{\omega}}}_{\mathit{R}}^{2}$/${\ensuremath{\gamma}}_{1}$${\ensuremath{\gamma}}_{2}$ is large compared to unity. Here ${\mathrm{\ensuremath{\omega}}}_{\mathit{R}}$ is the Rabi frequency and ${\ensuremath{\gamma}}_{1}$ and ${\ensuremath{\gamma}}_{2}$ are the longitudinal and transverse relaxation rates. In the weak pump case the LFC manifests itself as a fixed or static frequency shift. When the pump is strong, the response is independent of the LFC. At intermediate pump intensities the effect of LFC is dependent on the intensity of the pump. Both line-shift and line-shape distortions are present. The LFC thus gives rise to a shift in the resonance response that varies according to the intensity and frequency of the applied radiation. We call this effect the dynamic Lorentz shift.

Effect of local-field correction on a strongly pumped resonance.

We present a general formalism that incorporates local-field corrections into Bloch's equations and use it to calculate the strong-field susceptibility of a pressure-broadened gas consisting of two-level atoms. The major effect is to introduce a dynamic Lorentz shift that varies throughout the resonance line shape. We also calculate the susceptibility associated with a weak field (probe) in the presence of a strong field (pump) when the pump and probe are at the same frequency. Here the effect is to introduce both a variable shift and a greater distortion of the line shape.

Optical properties of monolayer NbS2 suspensions

We present a theory for the anisotropic optical and magnetic properties of monolayer NbS2 platelets suspended in water and oriented in a magnetic field. We compare experimental data obtained by Liu and Frindt and calculated properties using a dielectric function obtained from a Drude–Lorentz fit to reflectivity data for the bulk material. The anisotropic magnetic susceptibility of the material allows a separate study of the extinction coefficients of light with polarizations perpendicular and parallel to the flake plane. We estimate the contributions from scattering and absorption using the fitted dielectric constant; and we find that for monolayer flakes, absorption should be the dominant mechanism. We also estimate the effects of local-field corrections on absorption and scattering to be small. A puzzling feature is that the experimental ratio of the optical anisotropy for the extinction coefficients fails to satisfy a predicted 2:1 ratio suggested by symmetry considerations.

Oscillator models for multiphoton optical bistability and phase conjugacy

Nonlinear oscillator models are constructed to treat the bistability in situations involving elementary excitations in solids. Such models are shown to be useful not only in describing single photon but also multiphoton bistability. The resulting bistability both with and without cavity is considered. The two-photon excitonic bistability in CuCl is in detail. The effect of local field corrections can also be incorporated, in a simple manner, in such models.

The effect of local field corrections on the general band motion

The question of local field corrections to a general band motion of electrons involving both intraband and interband transitions is investigated. It is shown that when interband transitions is considered, local field type corrections will appear in the usual Boltzmann transport equation.

The effect of local-field correction on the transport properties of crystals

The question of local-field correction to the electrical transport is studied in more detail; namely, for the hopping limit and the band limit. In the hopping limit, if the hopping takes place between crystallographically equivalent sites, the short-range and Lorentz contributions to the dipolar potentials cancel in taking the intersite energy difference, and the electric field appearing in the hopping conductivity is just the macroscopic field. However if the hopping takes place between crystallographically inequivalent sites the short-range contributions to the dipolar potentials at the two sites do not cancel although the Lorentz contributions do. This leads to local-field-type corrections. The resulting corrections are found to be negligible at low fields but considerable at higher fields. Similar results are found for the Hall mobility of the small-polaron and AC impurity hopping conduction. In the band limit, it is shown that when the motion occurs in one band the net electric field appearing in the transport equation is just the macroscopic field unmodified by the local-field corrections.

Role of matrix elements in the theoretical determination of generalized susceptibilities in metals

The role of matrix elements in the calculation of the generalized susceptibilities $\ensuremath{\chi}(\stackrel{\ensuremath{\rightarrow}}{\mathrm{q}})$ of metals is discussed using the results of an augmented-plane-wave energy-band calculation for the eigenvalues and eigenfunctions of Sc metal. The inclusion of the oscillator strength matrix elements is found to significantly alter the structure obtained for $\ensuremath{\chi}(\stackrel{\ensuremath{\rightarrow}}{\mathrm{q}})$ in the constant-matrix-element approximation. The effect of local-field corrections on the phonon anomaly in Sc and the observed magnetic ordering of dilute rare-earth Sc alloys are described; in the latter case, a crude estimate of this effect is found to restore a (broad) peak in $\ensuremath{\chi}(\stackrel{\ensuremath{\rightarrow}}{\mathrm{q}})$ at $\stackrel{\ensuremath{\rightarrow}}{\mathrm{q}}\ensuremath{\approx}[0,0,0.5(\frac{\ensuremath{\pi}}{c})]$, in good agreement with experiment.