Showing papers on "Free electron model published in 1974"
TL;DR: In this paper, the RPA is extended in the framework of linear response theory to allow for the treatment of a finite free electron gas and the dielectric function taking quantum size effects into account, is calculated and shown to be finite in the limit of small wavevectors.
Abstract: The RPA is extended in the framework of linear response theory to allow for the treatment of a finite free electron gas. The dielectric function taking quantum size effects into account, is calculated and shown to be finite in the limit of small wavevectors. The theory is applied to a simple free electron model for a small metal particle and analytical expressions are obtained for the electronic polarizability of a thin film and for the optical properties in the plasma resonance region.
86 citations
TL;DR: In this article, the electron-diffusion Seebeck coefficient of dilute alloys is investigated in a simple model in which free electrons are scattered by phonons or by substitutional impurities bound in the lattice.
Abstract: The electron-diffusion Seebeck coefficient of metals and dilute alloys is investigated in a simple model in which free electrons are scattered by phonons or by substitutional impurities bound in the lattice. Second-order corrections to the $T$ matrix for electron scattering involving intermediate virtual phonon states are found to be of small magnitude but to have a very strong energy dependence. They thus make a large contribution to the thermoelectric coefficients while leaving the conductivities essentially unaltered. The pronounced temperature dependence of these second-order contributions allows an interpretation of experimental results that relies less on the phonomenon of phonon drag then has previously been the case.
55 citations
TL;DR: In this article, the degree of coupling between free electron and nitrogen vibrational temperatures in weakly ionized nozzle expansions of shock-heated nitrogen has been determined, and the resultant data were analytically correlated by coupling chemical nonequilibrium with nitrogen vibrations.
Abstract: The degree of coupling between free electron and nitrogen vibrational temperatures in weakly ionized nozzle expansions of shock‐heated nitrogen has been determined. Free electron temperatures were measured with Langmuir probes while nitrogen vibrational temperatures were determined with a new instrument based on the electron beam technique. The resultant data were analytically correlated by coupling chemical nonequilibrium with nitrogen vibrational and free electron temperature nonequilibrium. It was found that a vibrational loss factor of 7 × 10−4 and an effective translational‐rotational loss factor of 4.26 × 10−4 best predicted the measured electron temperature distributions.
46 citations
TL;DR: The optical properties of gallium quench condensed onto substrates at 10K, 30K and 80K have been studied in this article, where it was found that films condensed at 10k had a spectrum which could be described extremely well by the Drude equations.
Abstract: The optical properties of gallium quench condensed onto substrates at 10K, 30K and 80K have been studied. It is found that films condensed at 10K had a spectrum which could be described extremely well by the Drude equations. At higher temperatures two different spectra were observed, which the authors believe belong to the orthorhombic alpha dn and the monoclinic beta phases of gallium.
37 citations
TL;DR: In this paper, the conductivities of n-type inversion layers in (100) surfaces of p-type silicon were measured extensively as functions of electron density in the inversion layer, the ambient temperature and the applied magnetic field.
31 citations
TL;DR: In this paper, the electron momentum distribution at low momenta (<2 atomic units) shows considerable deviation from the free electron gas plus free atom core model, in agreement with recent γ-ray Compton scattering measurements.
Abstract: X-ray Compton scattering measurements on single crystals of aluminium indicate that the electron momentum distribution at low momenta (<2 atomic units) shows considerable deviation from the free electron gas plus free atom core model, in agreement with recent γ-ray Compton scattering measurements. The experimental results show an excess of momentum above the Fermi surface. Better agreement is obtained with the model of Pandey and Lam which includes electron-electron correlation and core orthogonalization effects, but a small discrepancy remains. No evidence of crystalline anisotropy was found in the results obtained from crystals with [110] and [111] scattering vector orientations.
27 citations
TL;DR: In this article, the electronic structure of noble or transition metal based alloys with transitional impurities was calculated using an hybridized tight binding and nearly free electron (TB-NFE) model for the host.
Abstract: The electronic structure is calculated, of noble or transition metal based alloys with transitional impurities, using an hybridized tight binding and nearly free electron (TB-NFE) model for the host. In this Hartree-Fock model for which parameters appear only in the host band structure, the author studies selfconsistently the screening of one isolated impurity and of two nth neighbouring impurities (n=1,...,4) in copper. The results are compared with those deduced in the Friedel-Anderson model from the asymptotic approximation: the charge oscillations and the spin polarizations on the nearest neighbours around an impurity cannot be rigorously obtained by the previous asymptotic approximation which does not take into account the selection rules required by the crystal symmetry.
24 citations
Journal Article•
01 Jan 1974-Science reports of the Research Institutes, Tohoku University. Ser. A, Physics, chemistry and metallurgy
TL;DR: In this article, the authors measured spin wave resonance for a series of fcc Fe-Ni alloys in order to study the exchange stiffness constant D, which is considered to be due to the inhomogeneous demagnetizing field of the sample.
Abstract: Spin wave resonance for a series of fcc Fe-Ni alloys has been measured in order to study the exchange stiffness constant D . In general the resonance field vs the square of the spin wave mode number ( n ) curve is linear for high values of n , whereas some amount of deviation from linearity occurs for low values of n . This is considered to be due to the inhomogeneous demagnetizing field of the sample. We can determine the value of D from the linear part of the curve, provided we have a sufficient number of observed modes. As a supplementary means, we have also made low temperature magnetization measurements from which the value of D was derived. Consistency between these two kinds of measurements is ascertained. The composition dependence of D is not quite coincident with that derived from the neutron small angle scattering experiments by Hatherly et al. The data are discussed both from the standpoint of localized electron model and collective electron model.
23 citations
TL;DR: In this article, a new emission line from ZnO was observed under strong uv-excitation at 42 K, which shifts to longer wavelengths with increasing excitation, and the experimental results were described by a model involving the recombination of a bound exciton which transferred part of its energy to a free electron.
17 citations
11 citations
TL;DR: In this article, a microwave photocreated cyclotron resonance signal is observed in p -type GaSb in the temperature range 1 −30 K. The problem of a surface effect on the measured peak position, reported for the first time is avoided by bulk carrier creation.
TL;DR: In this article, the authors measured the reflectivity spectrum of silver subfluoride, Ag 2 F, from 9,000 A (1.377 eV) to 3,000 AA (4.132 eV).
Abstract: Optical reflectivity spectrum of silver subfluoride, Ag 2 F, is measured from 9,000 A (1.377 eV) to 3,000 A (4.132 eV) at room temperature. The spectrum shows typical metallic features which are expected from Drude's classical free electron theory in metal; the reflectivity is fairly high and constant against wavelength in the long wavelengths region, while it decreases rapidly, almost to zero, at the specific wavelength which is known as “the UV window”. The optical constants are calculated from the reflectivity spectrum, and the real part of the complex dielectric constant is found to be zero at the photon energy of 2.572 eV (4,520 A); which is the plasma criterion of the free electron gas in the metal.
TL;DR: In this paper, a quasi-elastic electron scattering from 12 C in the range of four-momentum transfer 5 fm−2 ≦ q 2 ≦ fm −2 was measured and the momentum distribution of the bound state protons derived from this experiment showed a large tail of high momenta.
TL;DR: In this article, the Boltzmann equation for impurity and electron phonon scattering at the same time yields a deviation from Matthiessen's rule (MR) for the thermal conductivity of polyvalent metals with nonmagnetic impurities.
Abstract: Deviations from Matthiessen's rule (MR) for the thermal conductivity of polyvalent metals with nonmagnetic impurities are explained by two effects: (i) Even for a free electron model the energy dependence of the solution of the Boltzmann equation is not well approximated by the variational ansatz. Solving the Boltzmann equation for impurity and electron phonon scattering at the same time yields a deviation from MR, whose concentration and temperature dependence does not follow simple power laws. This effect is large enough to be measurable. (ii) The larger contribution is due to the angular dependence of the solution of the Boltzmann equation on a disconnected Fermi surface like that of Al where Umklapp scattering at the zone boundaries has to be taken into account. A simple theory based on a relaxation time approximation of the Boltzmann equation yields a rather large effect of the size found in experiments.
TL;DR: In this article, the phonon detectors were calibrated with an auxiliary second sound pulse in superfluid helium to verify that transverse heat pulses propagating in InSb suffer no attenuation from the free electrons.
TL;DR: In this paper, the magnetic susceptibility of the noninteracting electron gas has been studied on the basis of free electrons and the tight-binding model, with application to the properties of organic conducting materials.
Abstract: The magnetic susceptibility of the noninteracting electron gas has been studied on the basis of free electrons and the tight‐binding model, with application to the properties of organic conducting materials. Theoretical curves of susceptibility versus temperature are presented. The gradual transition from low temperature Pauli paramagnetism to the high temperature Curie law region is shown. In the transition region, the one‐dimensional systems show a peak in the susceptibility of the order of 110% of the low temperature limit. The magnetic susceptibility of the compound BDP(TCNQ)2 is interpreted in terms of a one‐dimensional tight‐binding model with an energy bandwidth of 0.07 eV.
TL;DR: In this article, a new scheme of radiative transitions for the copper-induced 1.35 eV emission band (it includes electron transitions from shallow donors to acceptors located below the neutral copper atom levels) is proposed.
Abstract: The copper-induced 1.35 eV emission band in p-GaAs with predominantly neutral copper atoms exhibits a marked decrease of intensity as the temperature is increased. These results cannot be satisfactorily explained by the previous model for the 1.35 eV emission band as arising from the free electron radiative transitions to neutral copper atoms. To explain consistently the observed results a new scheme of radiative transitions for the copper-induced 1.35 eV emission band (it includes electron transitions from shallow donors to acceptors located below the neutral copper atom levels) is proposed.
[Russian Text Ignored].
TL;DR: In this article, it is shown that there are always thin localized regions close to the electrode walls, where the free electrons are not in thermal equilibrium with the rest of the gas, even when the working fluid is such an effective absorber of electron energy as CO 2 or coal combustion products.
Abstract: Localized regions close to the electrode walls of open-cycle MHD generators have high enough current density so that the free electrons are not in thermal equilibrium with the rest of the gas, even when the working fluid is such an effective absorber of electron energy as CO 2 or coal combustion products. The over-all electrical performance of open-cycle MHD generators depends critically on the presence and behavior of such thin nonequilibrium regions adjacent to the electrodes. These effects are demonstrated and analyzed by means of previously developed numerical modeling techniques. PEN-CYCLE magnetohydrodynamic (MHD) generators are customarily viewed as devices in which the electrons are in thermal equilibrium with the heavy components of the gas. Accordingly, the term "equilibrium generators" is often used when referring to such generators. The present paper examines whether electron equilibrium is indeed achieved throughout the geometry of such generators. It is shown that there are always thin localized regions close to the electrode walls, where the electrons are not in thermal equilibrium with the gas, even when the working gas is an extremely effective absorber of electron energy, such as coal combustion products; the term "equilibrium generator" can be applied with validity only to the core of the flow, where there are no current concentrations; at the electrode "hot spots," where the current concentrates and the gas temperature may be considerably lower than in the core of the flow, the electron temperature elevation in such generators can reach several hundred degrees Kelvin. The effect of these localized nonequilibrium regions on the electrical performance of opencycle, combustion-gas-driven, MHD generator channels is assessed in this paper by the numerical modeling methods described in Ref. 1. Before we present the results of the detailed numerical modeling, however, it is useful to give a simple estimate of the elevation of the electron temperature Te above the characteristic temperature of the gas T in collision-dominated plasmas, and to define a characteristic parameter, / that can be used for order-ofmagnitude estimates. For this purpose, we shall employ the electron energy equation in the simplified form of an algebraic balance between the local Joule dissipation in the gas E' • J and the rate of energy transfer between the free electrons and the heavy particles Re(2) = %knevtdefi(Te- T}. This results, in the first approximation,2 in the simple expression (Te- T)/T = (y/3)/(l -K J2Af w2 jCAcff
TL;DR: In this article, a comparison of electron temperature and density made with Langmuir probes are compared to those made by Thomson scattering is made over a range of electron density (0.3−1.6) and temperature (1−2 eV).
Abstract: Measurements of electron temperature and density made with Langmuir probes are compared to those made by Thomson scattering. The comparison is made over a range of electron density [(0.3−1.6)×1015 cm−3] and temperature (1–2 eV). The two diagnostic techniques agree to within 20% in the case of the electron temperature and to within 10% in the case of the electron density.
TL;DR: In this article, the free-to-bound peak energy of CdS was investigated in terms of free-carrier screening, which reduced the binding energy of the acceptor.
Abstract: The luminescence spectrum of CdS consists of a number of sharp lines from 2.43 eV to the band edge at 2.58 eV and a number of broad bands below 2.43 eV. The highest energy broad band is due to a free electron recombining with a hole bound at a shallow acceptor (free to bound). The dependence of the free to bound peak of energy on temperature and excitation intensity is investigated in the interval 4.2–80 K. Increasing the excitation intensity results in a shift to higher energy. This is interpreted in terms of free carrier screening which reduces the binding energy of the acceptor. An energy shift due to the recombination of hot electrons is also considered. An often neglected donor–acceptor interaction term is discussed and found to be significant for an accurate measurement of the acceptor binding energy. Experimental observations suggest that screening of excitons due to free carriers is ineffective.
01 Jan 1974
TL;DR: In this article, an exact closed-form solution of a model for excitons in degenerate semiconductors is presented, where the optical absorption and luminescence spectra reduce to the Coulomb exciton absorption and lumininescence in the limit of vanishing free conduction electron density.
Abstract: An exact closed-form solution of a model for excitons in degenerate semiconductors is presented. The optical absorption and luminescence spectra reduce to the Coulomb exciton absorption and luminescence (for both bound and continuum excitons) in the limit of vanishing free conduction electron density. In the high density limit, the free electron absorption and emission spectra are obtained. As the free conduction electron density decreases from infinite density, resonance-like structures appear and emerge from the continuum, forming bound exciton states. These continuum resonances should be observable in the absorption and emission spectra of degenerate semiconductors. As the model semiconductor becomes decreasingly degenerate, the optical spectra change continuously, with no evidence of an abrupt phase transition. The relation of this model to theories of x-ray spectra, Mott transitions, and enhanced interband transitions in free-electron metals is discussed.
TL;DR: In this paper, a free electron model was used to derive the relevant source terms in the nonlinear polarization of the SHG from centro-symmetric crystals, and the results of SHG were presented from alkali metal covered surfaces of Ge, Cu and Ag.
Abstract: Optical second harmonic generation (SHG) from centro-symmetric crystals is restricted to the surface. A free electron model is used to derive the relevant source terms in the nonlinear polarization. Results of SHG from alkali metal covered surfaces of Ge, Cu and Ag are presented. A mono-layer of Na on Ge caused a tenfold increase in SHG. Drastic variations in SHG with Na deposition on Cu surfaces are attributed to the shifting of surface electronic states relative to the Fermi level.
TL;DR: In this paper, a generalized Boltzmann equation was derived for a system of free electrons, interacting with both phonons and imperfections, and the mobility of the free electrons was analyzed for monovalent metals.
TL;DR: In this article, the effect of varying the magnitude of the electron-atom cross section on nonequilibrium shock-wave structure was analyzed for argon-like gas at 1 cm-Hg and 300°K.
Abstract: The exact value of the electron-atom collisional ionization cross section for argon is not accurately known. The purpose of the present research is to determine numerically the effect of varying the magnitude of the electron-atom cross section on nonequilibrium shock-wave structure. Mach 18 shock waves propagating into an argon-like gas at 1 cm-Hg and 300°K have been analyzed. Thermal, ionizational, and excitational non-equilibrium are considered in the relaxation region behind the shock wave. Electrons in the relaxation region are formed by a two-step collisional process, wherein the atom is first excited and then it is ionized. The precursor is formed by ground and excited state continuum radiation and line radiation which is emitted, but not reabsorbed, in the region behind the shock wave. When the electron-atom ionization cross section is varied from 1·86 × 10−4 to 1·86 × 10−2 cm2/erg, the results show that (1) it influences the coupling between the precursor and relaxation region through the radiative source functions, (2) it does not influence the distance necessary to attain equilibrium behind the shock wave, (3) it inversely influences the magnitude of the precursor ionization, and excitation, and (4) it inversely influences both the free electron and excited state population in the relaxation layer.
TL;DR: In this article, the surface-plasmon properties of two disordered binary alloy systems, Al-Ag and Al-Au, were studied using their surface-pulses.
TL;DR: In this article, the energy spectrum and the angular correlation distributions for the reaction 12 C(e, e'p) 11 B are calculated within the framework of DWBA using spherical Hartree-Fock wave functions.
TL;DR: In this article, a simple itinerant electron model including the coupling with phonons can account for the static strain wave in pure chromium observed by X-ray below the Neel point.
TL;DR: In this article, the sensitivity of non-equilibrium shockwave structure to uncertainties in the ground and excited state continuum radiative cross section and the bound-bound cross section in a three level (ground, excited, and free electronic states considered) argon-like gas at Mach 18 and a pressure of 1 cm Hg.
Abstract: This numerical study investigates the sensitivity of non-equilibrium shockwave structure to uncertainties in (a) the ground and excited state continuum radiative cross section and (b) the bound-bound radiative cross section in a three level (ground, excited, and free electronic states considered) argon-like gas at Mach 18 and a pressure of 1 cm Hg. Changing the values of the radiative cross sections by an order of magnitude does not significantly influence the relaxation region; however, a large change occurs in not only the magnitude but also the extent of both the electron and excited state precursors. Increasing either the ground state continuum or the bound-bound cross section decreases the number of free electrons in front of the shock wave. These cross sections also influence the extent of the electron precursor through their influence on the ratio of the electrons produced by ground state photoionization to those produced by ground state photoexcitation followed by excited state photoionization. The bound-bound cross section also controls the excited state precursor, because the production of excited states is entirely due to line radiation. Increasing the excited state photoionization cross section increases both the magnitude and extent of the electron precursor, because the cross section influences the ratio of the two processes that compete to produce free electrons, and at the same time it influences the magnitude of the excited state precursor.
TL;DR: In this paper, it was shown that in the conditions for hole trapping new slow domains may propagate from the anode to the cathode in high-doped Gunn diodes in the presence of even a small concentration of mobile holes.
Abstract: It is shown that in the conditions for hole trapping new slow domains may propagate from the anode to the cathode in high-doped Gunn diodes in the presence of even a small concentration of mobile holes (much less than that of free electrons). The slow domain velocity is much less than the electron velocity outside the domain and is proportional to the mobile hole concentration. The conditions of the slow domain propagation are analysed and the slow domain parameters are calculated.