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.     

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.     

Dynamical exchange effects in a two-dimensional many-polaron gas

We calculate the influence of dynamical exchange effects on the response properties and the static properties of a two-dimensional many-polaron gas. These effects are not manifested in the random-phase approximation which is widely used in the analysis of the many-polaron system. Here they are taken into account by using a dielectric function derived in the time-dependent Hartree-Fock formalism. At weak electron-phonon coupling, we find that dynamical exchange effects lead to substantial corrections to the random-phase approximation results for the ground state energy, the effective mass, and the optical conductivity of the polaron system. Furthermore, we show that the reduction of the spectral weight of the optical absorption spectrum at frequencies above the longitudinal optical phonon frequency, due to many-body effects, is overestimated by the random-phase approximation.Received: 24 December 2003, Published online: 9 April 2004PACS: 71.45.Gm Exchange, correlation, dielectric and magnetic response functions, plasmons - 71.10.Pm Fermions in reduced dimensions (anyons, composite fermions, Luttinger liquid, etc.) - 71.38.Fp Large or Fröhlich polarons     

Application of a dielectric function to the exchange energy and specific heat of a two-dimensional electron gas

A new theory based on a dielectric function and its sum rule is presented for the exchange energy and specific heat of a two-dimensional electron gas. The results are exact towards absolute zero.     

Screening effects in two-dimensional electron gas

The potential produced by a charged impurity at the interface of a highly doped GaAlAs and GaAs is calculated at a finite temperature. The electron gas formed at the interface is described as a two dimensional gas in which the impurity is assumed to be dipped. Temperature dependence of the impurity potential is calculated in the random phase approximation (R.P.A.) as well as in the modified temperature dependent Thomas-Fermi (M.T.T.F.) approximation which is defined to include temperature effects and to reduce to Thomas-Fermi result at zero temperature. The binding energy of the impurity for the ground state is calculated in R.P.A. and in M.T.T.F.. It is shown that at temperature T, much larger than the Fermi temperature, T_F, M.T.T.F. gives binding energies close to R.P.A. results.     

Many-body effects in spin-polarized two-dimensional electron gas

Many-body effects on the spin polarization are studied in an n channel inversion layer on Si (1 0 0) surface in a magnetic field parallel to the surface in random phase approximation. The spin polarization exhibits a discrete jump to a full polarization at the critical magnetic field in the low-density regime and the critical field is reduced considerably from that estimated by an extrapolation based on the zero-field susceptibility.     

Magnetic ratchet effects in a two-dimensional electron gas

The effect of the magnetic field on the generation of an electric current in a two-dimensional electronic ratchet is theoretically studied. Mechanisms of the formation of magnetically induced photocurrent are proposed for a structure with a two-dimensional electron gas (quantum well, graphene, or topological insulator) with a lateral asymmetric superlattice consisting of metallic strips on the external surface of the structure. The ratchet with the spatially oscillating magnetic field generated by the ferromagnetic lattice, as well as the nonmagnetic ratchet placed in the uniform magnetic field both classically weak and strong quantizing, is considered. It is established that the ratio of the amplitude of the magnetic oscillations of photocurrent to the ratchet photocurrent in zero field can exceed two orders of magnitude.     

The influence of the surface roughness on dielectric function of two-dimensional electron gas: a Lindhard model approach

Low field response function calculations have been performed on a two-dimensional electron gas with well-defined electron-surface roughness scattering. The Lindhard model was employed to compute the response function. In particular, detailed investigations were made on the system searching for an interplay between surface roughness with well-defined correlation function, (characterizes by asperity height and correlation length) spatial confinement and the dielectric function. We analyze to what extent the normal behavior and functionality of dielectric function of two-dimensional devices are modified by random scattering events caused by the contribution from the surface roughness. Results of the current work indicate that contribution of the surface roughness on scattering and absorption process could not be considered as an underestimating effect. We find, however, that functionality of the dielectric function seems to be quite independent of the particular roughness features.     

HgMnTe磁性二维电子气自旋-轨道和交换相互作用研究

通过分析不同温度下HgMnTe磁性二维电子气Shubnikov-de Hass（SdH）振荡的拍频现象，研究了量子阱中电子自旋 轨道相互作用和spd交换相互作用.结果表明：（1）在零磁场下，电子的自旋 轨道相互作用导致电子发生零场自旋分裂；（2）在弱磁场下，电子的自旋-轨道相互作用占主导地位，并受Landau分裂和Zeeman分裂的影响，电子的自旋分裂随磁场增加而减小；（3）在高磁场下，电子的spd交换相互作用达到饱和，电子的自旋分裂主要表现为Zeeman分裂.实验证明了当电子的Zeeman分裂能量与零场 关键词： 磁性二维电子气 Zeeman分裂 Rashba自旋分裂     

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.     

Gigantic exchange enhancement of spin g-factor for two-dimensional electron gas in GaAs

Gigantic, oscillatory values of the spin g-factor for two-dimensional electron gas in GaAs have been measured, using the Shubnikov-deHaas effect in GaAs - Al_0.3Ga_0.7As heterojunctions. The effect has been attributed to the exchange interaction and compared with the theory of Ando and Uemura. The observed g-factor enhancement is, together with the fractional quantum Hall effect, the strongest evidence for the decisive role of many-body interactions in the 2D electron gas.     

Dynamical response properties of a two-dimensional electron gas in a weak periodic magnetic modulation

Calculating the dynamical dielectric response function for a two-dimensional electron gas (2D EG) under a perpendicular magnetic field and subjected to an additional weak unidirectional periodic magnetic field within the random-phase approximation (RPA), we find that not only is the response function broadened in the presence of the magnetic modulation, but it is also found to contain a series of subsingularities at the band edges which are attributed to the magnetic modulation induced broadening of the energy spectrum.     

Damping effects and the metal-insulator transition in a two-dimensional electron gas

The damping of single-particle degrees of freedom in strongly correlated two-dimensional Fermi systems is analyzed. Suppression of the scattering amplitude due to the damping effects is shown to play a key role in preserving the validity of the Landau-Migdal quasiparticle picture in a region of a phase transition associated with the divergence of the quasiparticle effective mass. The results of the analysis are applied to elucidate the behavior of the conductivity σ(T) of the two-dimensional dilute electron gas in the density region where it undergoes a metal-insulator transition.     

Wigner function of a two-dimensional electron gas in a magnetic field

The Wigner function of a two-dimensional electron gas in an arbitrary magnetic field perpendicular to the plane in which the electrons are confined is constructed rigorously. The function is useful in taking various statistical averages and illuminates the roles played by the hyperbolic functions of the field which appear in the expressions of the susceptibility and other physical quantities.     

Magneto-excitations in the rotating two-dimensional electron gas

Summary The effects of a rigid rotation on the two-dimensional electron gas are studied. For very large wavelengths the lower branch of magneto-excitations has the dispersion relationE_(k)≈[ℏΓ (ℏΓ+ve ²|k|)]^1/2 , wherev is the filling factor and Γ the angular speed of rotation. The result holds independently of the presence of a solid phase (Wigner lattice) on the gas.

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Riassunto Si studiano gli effetti di una rotazione rigida su un gas di elettroni bidimensionale. Per lunghezze d'onda molto ampie, il ramo piú basso delle eccitazioni magnetiche ha la relazione di dispersioneE_(k)≈[ℏΓ (ℏΓ+ve ²|k|)]^1/2 dovev è il fattore di riempimento e Γ la velocità angolare di rotazione. Il risultato vale indipendentemente dalla presenza di una fase solida (reticolo di Wigner) nel gas.

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Резюме Исследуется влияние жесткого вращения на двумерный электронный газ. Для очень больших длин волн низшая ветвь магнитных возбуждений имеет дисперсионное соотношениеE_(k)≈[ℏΓ (ℏΓ+ve ²|k|)]^1/2, гдеv-фактор заполнения и Γ-угловая скорость врашения. Полученный результат оказывается справедлив в присутствии твердой фазы (решетка Вигнера).

     

Longitudinal dielectric behavior of a harmonically bound two-dimensional electron gas in a uniform magnetic field

We have employed random-phase approximation to determine the inverse dielectric function for a harmonically confined two-dimensional electron gas in a magnetic field. We examine the plasmon dispersion relation and show the results for the variation of plasmon frequency with the magnetic field strength and confinement energy.