scispace - formally typeset
Search or ask a question

Showing papers on "Free electron model published in 1989"


Journal ArticleDOI
TL;DR: The electronic and optical properties of the ground state of the excitonic trions corresponding to an exciton bound to an electron or a hole are studied theoretically for 2D semiconductors in the whole range of the electron-to-hole effective mass ratio.

158 citations


Journal ArticleDOI
TL;DR: In this paper, the wave-vector and frequency-dependent energy loss function was used to calculate electron stopping powers and electron inelastic mean free paths in solids for energies between 1 eV and 10 keV above the Fermi energy.

126 citations


Journal ArticleDOI
TL;DR: The volume plasmon dispersion showed strong deviations not only from the random-phase approximation, but also from the predictions of the current theories for Fermi liquids, including short-range exchange and correlation, which are at variance with recently published enhancement of the band mass for the occupied states.
Abstract: To study the dynamical response of the valence-electron gas in nearly-free-electron metals, we carried out an electron-energy-loss investigation on Na, K, Rb, and Cs. On polycrystalline samples we measured the volume plasmon dispersion, which showed strong deviations not only from the random-phase approximation, but deviations as well from the predictions of the current theories for Fermi liquids, including short-range exchange and correlation. In addition, anomalous dispersion of the plasmon half-width was found. Both results may be traced back to exchange and correlation effects not properly treated by the current Fermi-liquid theories. Furthermore, we observed the excitation of intraband transitions in Na and Rb, the dispersion of which yields the effective band mass for unoccupied states. The results for Na are at variance with recently published enhancement of the band mass for the occupied states. To elucidate the influence of band structure, measurements were also performed on a single-crystalline Na film and we observed the so-called zone-boundary collective state in Na.

120 citations


Journal ArticleDOI
TL;DR: In optical experiments with laterally patterned GaAs quantum wells, the Fermi energy as well as subband spacings are obtained and the linear free-electron density is determined.
Abstract: In optical experiments with laterally patterned GaAs quantum wells we observe confinement of free carriers to motion in one dimension. Optical recombination of band-gap transitions shows that free electrons and holes are confined in spatially indirect type-II multiple quantum wires. Resonant-inelastic-light-scattering spectra show intersubband excitations of the one-dimensional electron gas. From the optical measurements we obtain the Fermi energy as well as subband spacings and determine the linear free-electron density

79 citations


Journal ArticleDOI
TL;DR: Luminescence at energy lower than the absorption edge has been investigated in crystals of GaSe, containing different degrees of lattice disorder, as a function of temperature, of photoexcitation intensity, and of excitation energy.
Abstract: Luminescence at energy lower than the absorption edge has been investigated in crystals of GaSe, containing different degrees of lattice disorder, as a function of temperature, of photoexcitation intensity, and of excitation energy. At low excitation intensity, the extrinsic luminescence is composed of broad overlapping bands that present a blue shift when the temperature increases. Their shape and intensity is strongly dependent on the laser excitation frequency and on the degree of lattice disorder. The results are discussed in terms of a model involving the recombination of shallow donors and free electrons with deep acceptors. These two recombination mechanisms and those involving free and bound excitons are found to be competitive. Their relative importance is strongly dependent on the concentration of structural defects, on the temperature, on the excitation intensity, and on the excitation frequency.

72 citations


Journal ArticleDOI
TL;DR: Inclusion of exchange and correlation effects in the dielectric matrix is shown to decrease the bandwidth relative to the random-phase-approximation result by a significant amount, and local-field effects are found to have little effect on the quasiparticle band structure of these simple metals.
Abstract: The quasiparticle excitation spectrum is calculated for the nearly-free-electron metals Li, Na, and Al by evaluation of the electron self-energy operator within the GW approximation and a generalized plasmon-pole model. The calculated quasiparticle energies for Na and Al are in excellent agreement with angle-resolved photoemission experiments. For Na in particular, the occupied-band width is significantly narrower than the free-electron value, as found in experiment. Inclusion of exchange and correlation effects in the dielectric matrix is shown to decrease the bandwidth relative to the random-phase-approximation result by a significant amount. Local-field effects, reflected in the off-diagonal elements of the dielectric matrix, are found to have little effect on the quasiparticle band structure of these simple metals.

55 citations



Journal ArticleDOI
TL;DR: A classical phase-space model of the hydrogen molecule is presented and applied to the study of the electron-capture and -ionization processes in collisions of fully stripped ions with H{sub 2} at intermediate impact energies and charge states from 1 to 10.
Abstract: A classical phase-space model of the hydrogen molecule is presented and applied to the study of the electron-capture and -ionization processes in collisions of fully stripped ions with ${\mathrm{H}}_{2}$ at intermediate impact energies and charge states from 1 to 10. The model is based on the independent-electron and the impact-parameter approximations. The electron--impinging-ion and electron--target-nuclei interactions are exactly taken into account. The interaction between the electrons is approximated by model potentials. The calculated total cross sections for production of free electrons and capture of one electron are in good agreement with different experimental data. The ratio between the capture cross sections from molecular and atomic hydrogen targets is also analyzed and compared with available empirical scalings. It is found that this ratio varies from a value less than 1 at low impact energy to 4 at higher energies. The reasons for these differences are discussed. A comparison is made between the capture cross sections for different orientations of the hydrogen molecule.

42 citations


Journal ArticleDOI
TL;DR: In this paper, the nature of the electronic eigenstates for an excess electron in pure water in the absence of solvent reorganization is investigated using solvent configurations generated from molecular dynamics simulation of liquid water at 283 K and a previously developed electron-water molecule pseudopotential.

41 citations


Journal ArticleDOI
TL;DR: In this paper, the results of a work function, LEED, and electron energy loss study of the adsorption of Li, Na, K, Rb, and Cs on Al(111) were reported.

39 citations


Journal ArticleDOI
TL;DR: No evidence of electron-impact ionization and ensuing avalanche formation is found up to the intrinsic damage threshold in NaCl and SiO2 under prebreakdown conditions.
Abstract: Free-electron absorption of 1064-nm photons is measured photoacoustically in NaCl and ${\mathrm{SiO}}_{2}$. The electrons are generated with a 266-nm pump pulse by two- or three-photon transitions. For a given pump pulse energy, the photoacoustic signal and the rise in lattice temperature are observed as a function of the energy of the 1064-nm pulse and found to be in agreement with the theory of free-carrier heating. Temperatures approaching the melting point are produced in these materials under prebreakdown conditions. No evidence of electron-impact ionization and ensuing avalanche formation is found up to the intrinsic damage threshold.

Book ChapterDOI
01 Jan 1989
TL;DR: A review of recent results that highlight applications of the light scattering method in studies of quasi-two-dimensional electron systems can be found in this paper, where the authors have shown that the method can be used to measure the excitations associated with the free electron motion in the plane as well as that of the restricted motion normal to the plane.
Abstract: We have presented a review of recent results that highlight applications of the light scattering method in studies of quasi-two-dimensional electron systems. We have seen that the method can be used to measure the excitations associated with the free electron motion in the plane as well as that of the restricted motion normal to the plane. These features, in conjunction with the very advantageous option to measure spectra of collective and single particle excitations, make light scattering a very versatile spectroscopic tool. With the use of optical multichannel detection, and taking advantage of large resonant enhancements, it is possible to carry out experiments at very low laser power densities. This creates the possibility to study remarkable low temperature many-body phenomena, like the fractional quantization of the Hall effect, that are at the frontier of condensed-matter physics. We expect important applications in the area of time-resolved spectroscopy, where the method could reveal dynamical behavior of hot electrons. There is increasing interest in systems where the electrons have one-dimensional behavior (quantum wires) and also in zero-dimensional systems (quantum dots). We expect that inelastic light scattering, especially with the new techniques of micro-Raman spectroscopy, will play a prominent role in the elucidation of the intriguing properties of these novel semiconductor microstructures.

Journal ArticleDOI
TL;DR: In this article, the dc-conductance of a ballistically behaving electron system of a finite width is quantised in units ofe2/h, independent of the length of the system, and can be observed experimentally by changing the Fermi energy, the geometrical width, and the magnetic field, alternatively.
Abstract: It is shown that the dc-conductance of a ballistically behaving electron system of a finite width is quantised in units ofe2/h. The quantisation is independent of the length of the system, and can be observed experimentally by changing the Fermi energy, the geometrical width, and the magnetic field, alternatively. Two novel quantum phenomena are predicted. In the presence of weak disorder there are anti-resonances which separate neighboring conductance plateaus. The ac-conductance shows oscillations which can be assigned to interference of free electron states.

Journal ArticleDOI
TL;DR: In this article, it was shown that the Fermi energy is proportional to the free electron concentration to the power 2/3, characteristics for degenerate electron statistics, and that tributyltin trifluoroacetate gives the best results with mobilities of the order of 5 × 10 -3 m 2 V -1 s -1 and carrier concentrations of about 2.5 × 10 26 m -3.

Journal ArticleDOI
TL;DR: The average degree of ionization for a dense plasma is calculated with the aid of a newly established atomic model based on the Thomas-Fermi (TF) method, corresponding to models of increasing sophistication for the ion-ion correlation function.
Abstract: The average degree of ionization for a dense plasma is calculated with the aid of a newly established atomic model based on the Thomas-Fermi (TF) method. This new model is characterized by the following features: (i) the bound electrons and free electrons are treated separately, (ii) a physically reasonable definition of the bound electrons is given, (iii) the system is described as a strongly coupled plasma of free electrons and TF ions, (iv) the source density in the Poisson equation is determined by the electron-ion and ion-ion correlation functions, and (v) the degree of ionization is calculated through the minimization of the total free energy. Results from the first and second approximations are presented, corresponding to models of increasing sophistication for the ion-ion correlation function. A comparison of these results with the results from earlier TF calculations and with the results from the Saha equation is also provided.

Journal ArticleDOI
TL;DR: The interstitial-electron model (IEM) for lattice dynamics in close-packed structures is proposed and test and the predicted phonon-dispersion relations are in excellent agreement with experiment for all branches in the high-symmetry directions.
Abstract: We propose and test the interstitial-electron model (IEM) for lattice dynamics in close-packed structures. The IEM model treats the valence electrons as classical lattice particles localized at interstitial tetrahedral positions, as suggested by the ab initio generalized-valence-bond cluster calculations of McAdon and Goddard. We apply the IEM to the fcc metals Ni, Pd, Pt, Ag, Au, and Cu using a simple six-parameter description (nearest-neighbor electron-electron, electron-ion, ion-ion terms, each with two parameters) to exactly fit lattice constants, elastic constants (C11,C12,C44), and the two lattice modes at the X point in the first Brillouin zone. The predicted phonon-dispersion relations are in excellent agreement with experiment for all branches in the high-symmetry [100], [110], and [111] directions. The explicit inclusion of valence electrons in the interparticle interactions implicitly includes what would be considered as many-body effects in the usual ion-ion scheme (e.g., C12≠C44). Such force fields should also be useful for describing nonperiodic systems (surfaces, clusters, and defects).

Journal ArticleDOI
TL;DR: In this paper, the dependence of free electron charging upon the gas, electric field, particle radius, and the charging parameter N 0 t has been measured, and a new high electron temperature continuum-regime field-diffusion charging model is presented which utilizes the Boltzmann relation as an approximate solution for the electron densities near the particle.

Journal ArticleDOI
TL;DR: A localized perturbation moving through a homogeneous electron gas with a constant velocity is studied and the time-dependent Schr\"odinger equation is solved by means of a Galileo transformation.
Abstract: A localized perturbation moving through a homogeneous electron gas with a constant velocity is studied. The time-dependent Schr\"odinger equation is solved by means of a Galileo transformation. The energy dissipation rate is expressed in terms of the transport cross section for arbitrary velocities, temperatures, and strength of the perturbation. Expressions for the electron density and the backflow pattern around the moving perturbation are given. Quantitative results are presented for a hard-sphere potential.

Journal ArticleDOI
TL;DR: In this paper, a novel concept for modulating far-infrared light is presented based on the "photon-plasmon, plasmon-photon" interaction with a thin layer of a free-electron gas in a n-doped semiconductor.
Abstract: A novel concept for modulating far‐infrared light is presented based on the ‘‘photon‐plasmon, plasmon‐photon’’ interaction with a thin layer of a free‐electron gas in a n‐doped semiconductor. For oblique incidence of p‐polarized light at the plasma frequency of the electrons, high‐reflection properties arise due to plasma resonance. The influence of all the constituent parameters (angle of incidence, electron mobility and density, thickness of the layer, etc.) on the reflectivity is discussed. The plasma frequency, and hence the reflectivity, can be modulated by changing the effective mass or the density of the electrons. This leads to a small, integrable, and fast modulable mirror, which can be used as a switching device (electrically or optically driven) or even as a way of frequency modulation.

Journal ArticleDOI
TL;DR: In this article, the growth of superradiant pulses in a helical-wiggler FEL was characterized using 1-D and 2-D numerical simulations, and the effects of detuning, energy spread, and axial current distribution on superradian pulses were analyzed.
Abstract: It has been suggested that slippage effects in a single-pass free electron laser can generate an output signal near the electron beam tail with a peak amplitude many times greater than the expected saturated value [1]. The growth of such “superradiant” pulses in a helical-wiggler FEL is characterized here using 1-D and 2-D numerical simulations. The 1-D calculations show the effects of detuning, energy spread, and the axial current distribution on superradiant pulses, while preliminary 2-D simulations illustrate the effects of betatron motion and the radial structure of the electron beam.

Journal ArticleDOI
TL;DR: In this article, the properties of ground states of an itinerant electron model (which can be regarded as the one-band, spinless Falicov-Kimball model) beyond the hole-particle symmetry point are studied.
Abstract: Properties of grounds states of an itinerant electron model (which can be regarded as the one-band, spinless Falicov-Kimball model) beyond the hole-particle symmetry point are studied. The underlying lattice is chosen to be a square lattice. Using exact and numerical arguments it is shown that when the density of band electrons is varied different sorts of periodic configurations of localized particles (f-electrons) minimize the energy. The one- particle densities of states of the band electrons corresponding to these configurations are presented. The system can be a metal or an insulator accordingly. Moreover, for some densities of band electrons a metal-insulator transition, driven by the unique parameter of the system, takes place. The importance of many-body effects is revealed.


Journal ArticleDOI
TL;DR: The model was used to interpret recently observed shifts in the K-shell photoabsorption-edge energy in shock-compressed aluminum and was further examined through comparisons with two average-atom, self-consistent-field calculations and an augmented-plane-wave calculation.
Abstract: A theoretical model for the calculation of the K-shell photoabsorption edge in a dense plasma is described. In the model, degeneracy and continuum lowering contributions due to free electrons and neighboring ions were treated as perturbations on the continuum and the bound state. These contributions were evaluated using first-principles solid-state methods. The model was used to interpret recently observed shifts in the K-shell photoabsorption-edge energy in shock-compressed aluminum. The validity of the model was further examined through comparisons with two average-atom, self-consistent-field calculations and an augmented-plane-wave calculation.

Journal ArticleDOI
TL;DR: In this paper, the authors investigated the two-carrier scattering mechanism in p-indium selenide by means of the temperature dependence of the Hall mobility and thermopower and determined the density of states effective mass in the valence band.
Abstract: Carrier scattering mechanisms in p-indium selenide are investigated by means of the temperature dependence of the Hall mobility (160–500 K) and thermopower (200–300 K). An anomalous behaviour of the Hall voltage, which changes sign below 215 K, is interpreted through the existence of planar aggregates of ionized shallow donor impurities that create potential wells behaving as deep donors and in which a low concentration of two-dimensional free electrons can exist. This fact is taken into account through equations for two-carrier Hall effect. Holes are found to be predominantly scattered by anA ′1 homopolar phonon with an energy of 27.8 meV. From thermopower results, the density of states effective mass in the valence band is determined,mdv*=(1.5±0.2)m0.

Journal ArticleDOI
TL;DR: In this paper, the authors measured the optical properties of free carriers in a-Si:H by pump and probe femtosecond spectroscopy and derived the upper bound for the mobility of free electrons approximately 100 meV above the mobility edge.
Abstract: We have measured the optical properties of free carriers in a-Si:H by pump and probe femtosecond spectroscopy. The Drude model is found to be applicable and the momentum scattering time that also enters in the expression for the mobility of the extended state carriers is of the order 0.6 femtosecond for electrons. The upper bound for the mobility of free electrons approximately 100 meV above the mobility edge is 6 cm 2 /V sec.

Journal ArticleDOI
TL;DR: It is concluded that transverse field profile modification due to space-charge waves may be significant in comparison to the optical guiding effect in Raman free-electron lasers.
Abstract: A comparative analysis of wave profile modification effects in Raman free-electron lasers is presented. The analysis is based on a 3D theoretical model that is valid in both Raman and Compton regimes. We study two companion effects, the optical guiding and the excitation of space-charge waves with transverse field components. Both effects are compared through exemplary parameters based on previous free-electron laser experiments. We conclude that transverse field profile modification due to space-charge waves may be significant in comparison to the optical guiding effect.

Journal ArticleDOI
TL;DR: In this article, the cross section for second harmonic scattering in the head-on collision of an intense laser beam with free electronics exhibits a marked forward-backward asymmetry, which is explained as an interference between the scattered fields produced by the linear and nonlinear components of the electron motion.

Journal ArticleDOI
TL;DR: In this article, the authors extended their previous theoretical treatment of the scattering of excitons by free electrons and holes in a two-dimensional semiconducting quantum well system to obtain the ionization cross section of the exciton in these structures.

Journal ArticleDOI
TL;DR: In this paper, it was shown that the single pass gain by stimulated bremsstrahlung of a lasing bunch in an envisioned two-beam wake-field cavity is sufficiently great to generate a coherent radiation in the soft X-ray region.

Journal ArticleDOI
TL;DR: In this paper, the Fermi level movement relative to the semiconductor band edges as a function of alkali metal coverage has been closely followed, and several criteria of metallicity are proposed.
Abstract: The interfaces of alkali metals (Cs and Rb) on GaAs and InP(110) surfaces prepared at 110 K low temperature have been studied using photoemission. At low temperature, multilayers of alkali metals with laminar growth can be obtained. The overlayer metallization is investigated by following the density of states near the Fermi cutoff, the free electron plasma loss, and the Fermi level movement at the semiconductor surfaces. Several criteria of metallicity are proposed. It is found that one monolayer of Cs or Rb is not metallic, and full metallicity is established at around two monolayers of coverage. The Fermi level movement relative to the semiconductor band edges as a function of alkali metal coverage has been closely followed. The semiconductor band bendings at low coverages are attributed to the surface‐donor states originating from alkali metal atom chemisorption. The Fermi level stabilization at these interfaces occurs when the overlayers become metallic. This pinning behavior is explained in terms of the metal‐induced gap states. The Fermi level pinning at the room temperature interfaces is also discussed and compared with the low‐temperature behavior.