Electron-phonon coupling in intrinsic trans-polyacetylene

We consider a valence force field model for the phonon spectrum of (CH)_x and find that phonon coupling to extended π electron states must be included to describe the observed Raman active modes of the polymer. The calculated phonon spectra are shown to possess the zone center dispersion anomalies characteristic of a condensed Peierls ground state.     

Electron-phonon coupling in armchair silicene nanoribbons

We report the effects of electron-phonon coupling on the charge density distribution of polarons in armchair nanoribbons of silicene by using an extended tight-binding model with lattice relaxation. The results show that the charge distribution in silicene nanoribbons is analogous to graphene and that the charge localization increases when the intensity of electron-phonon coupling also increases. We further show that silicene nanoribbons may be a conducting or semiconducting material, depending on both the width of the nanoribbon and the possibility of polaron formation. This contribution provides additional insight into the behavior of polarons in silicene nanoribbons, systems of great interest.     

Electron-phonon coupling in transition metals and resonant scattering

An explicit formula is derived for the electron-phonon coupling of transition metals in terms of parameters that are used in first principle transition metal band structure calculations. Its relevance and systematics are discussed.     

Electron-phonon coupling in highly doped n type silicon

The effect of free electrons on the optical phonon of silicon at the center of the Brillouin zone is studied using the Raman scattering technique. Heavy doping gives rise to a continuous electronic Raman scattering and makes the phonon line shape assymetric. The profile factor which is related to the disymetry, is shown to have the signes of the matrix elements of the electron-phonon interaction.     

Electron-phonon coupling and phonon generation in normal-metal microbridges

The second derivative of current—voltage characteristic, $\text{d}{}^2\text{I}\text{d}\text{V}{}^2$, of a small orifice connecting two pieces of normal metals is shown to be proportional to the function $\text{G(ω) =}\text{α}\text{?}{}^2\text{(ω)F(ω)}$ at ω = eV, where F(ω) is the phonon density of states, and α̃² (ω) the square of the electron—phonon matrix element averaged over the Fermi surface and multiplied by the additional structure factor taking into account the geometry of the orifice. The constriction is shown to work, in a current-carrying state, as a source of non-equilibrium phonons emitted in the immediate vicinity of the orifice.     

Electron-phonon scattering in transport properties of InSe single crystals

Summary The electron-phonon scattering in indium selenide single crystals has been investigated by Hall-mobility and Raman-spectroscopy measurements. The experimental data have been interpreted according to the Fivaz and Schmid model for homopolar optical scattering. The best fit of the experimental results is obtained by assuming the bidimensional behaviour of the interaction involving anA ₁ phonon with energy 14.5 meV. The bidimensional character is probably due to the presence of a large number of planar defects, confirmed by electron microscope observations, which strongly localize the carriers within the layers.

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Riassunto In questo lavoro è riportato uno studio dell'interazione elettrone-fonone in monocristalli di seleniuro di indio, condotto mediante misure di effetto Hall e spettroscopia Raman. I dati sperimentali sono stati interpretati secondo il modello di Fivaz e Schmid, per lo scattering da fononi ottici omopolari. L'approssimazione migliore delle curve sperimentali è ottenuta assumendo un carattere bidimensionale per l'interazione tra gli elettroni ed i fononi, nel modoA ₁, con energia 14.5 meV. Il carattere bidimensionale delle proprietà di trasporto è probabilmente dovuto alla presenza di difetti planari che localizzano i portatori di carica all'interno degli strati.

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Резюме Исследуется электрон-фононное рассеяние в монокристаллах InSe, используя измерения подвижности Холла и спектроскопии комбинационного рассеяния. Экспериментальые данные интерпретируются в соответствии с моделью Фиваца и Шмидта для гомополярного оптического рассеяния. Наилучшая подгонка экспериментальных результав получается в предположении двумерного характера взаимодействия между электронами и фононами, модыA ₁ , с энергией 14.5 мэВ. Двумерный характер, по-видимому, обусуовлен наличием большого числа плоских дефектов, которые сильно локализуют носители внутри слоев, что подтверждается наблюдениями электронной микроскопии.

     

Electron-phonon coupling with donor-acceptor pair recombination in polar semiconductors

An analysis of the electron-LO phonon interaction function S(R) for donor-acceptor pair transitions in polar semiconductors is presented. Contradicting theoretical results (S is a monotonically increasing function of pair separation distance R, ref. 2) with reliable experimental findings (S needs to be a drecreasing function of R, ref. 5) are removed, if the interaction between LO-phonons and the donor (acceptor) is taken into account more rigorously.     

Anisotropic dynamic response of pentacene single crystals

We have investigated the polarization and momentum dependence of singlet excitons in pentacene molecular crystals using inelastic electron scattering. Our results demonstrate that both the direction as well as the absolute value of the momentum are decisive for the spectral intensity of these excitons. Possible implications of this observation for a microscopic understanding of excitons in organic molecular crystals are discussed.     

Electron-phonon coupling and the soft phonon mode in TiSe2

We report high-resolution inelastic x-ray measurements of the soft phonon mode in the charge-density-wave compound TiSe(2). We observe a complete softening of a transverse optic phonon at the L point, i.e., q=(0.5, 0, 0.5), at T≈T(CDW). Detailed ab initio calculations for the electronic and lattice dynamical properties of TiSe(2) are in quantitative agreement with experimental frequencies for the soft phonon mode. The observed broad range of renormalized phonon frequencies, (0.3, 0, 0.5)≤q≤(0.5, 0, 0.5), is directly related to a broad peak in the electronic susceptibility stabilizing the charge-density-wave ordered state. Our analysis demonstrates that a conventional electron-phonon coupling mechanism can explain a structural instability and the charge-density-wave order in TiSe(2) although other mechanisms might further boost the transition temperature.     

Electron-phonon matrix elements and coupling constant λ in transition-metal alloys

It is shown that the two-center integrals c_ij and the degenerate three-center integrals d_im of the electron-phonon matrix elements influence the electron-phonon coupling constant λ of a transition-metal alloy in a different manner. This leads to interesting effects which may increase the critical temperature T_c. Numerical calculations within the framework of the Coherent Potential Approximation (CPA) are compared with experimental results.     

Electron-phonon coupling and monopolar charge fluctuations in intermediate valence TmSe

Polarized Raman spectra of intermediate valence Tm_xSe (x=0.95, 1.00, 1.01) have been measured. The scattering intensity is interpreted in terms of a one-phonon density of states weighted by the electron-phonon matrix element. The latter is described in a model of phonon-induced local, intraionic charge deformabilities. In the symmetry-analysed Raman intensities of A_1g character, two peaks near 8.8meV and 21.9meV are attributed to monopolar charge deformations of the valence-fluctuating Tm ions.     

Electron-phonon coupling constant of cuprate based high temperature superconductors

The electron-phonon coupling constant in two-dimensional cuprate high temperature superconductors has been determined by the ultrasonic method. The electron-phonon coupling constant in the Van Hove scenario was found to increase with transition temperature T_c. is in the range of 0.025-0.060 which is 10-100 times smaller than the conventional three-dimensional Bardeen-Cooper-Schrieffer coupling constant. The characteristic Debye temperature θ_D does not correlate with T_c. These findings show that the interplay between the Debye frequency and electron-phonon coupling in the two-dimensional system and their variations have a combined effect in governing the transition temperature.     

Electron-phonon coupling and its evidence in the photoemission spectra of lead

We present a detailed study of the influence of strong electron-phonon coupling on the photoemission spectra of lead. Representing the strong-coupling regime of superconductivity, the spectra of lead show characteristic features that demonstrate the correspondence of physical properties in the normal and the superconducting state, as predicted by the Eliashberg theory. These features appear on an energy scale of a few meV and are accessible for photoemission only by using modern spectrometers with high-resolution in energy and angle.     

Electron-phonon coupling in high-temperature cuprate superconductors determined from electron relaxation rates

We determined electronic relaxation times via pump-probe optical spectroscopy using sub-15 fs pulses for the normal state of two different cuprate superconductors. We show that the primary relaxation process is the electron-phonon interaction and extract a measure of its strength, the second moment of the Eliashberg function λ[ω2] = 800 ± 200 meV2 for La(1.85)Sr(0.15)CuO4 and λ[ω2] = 400 ± 100 meV2 for YBa(2)Cu(3)O(6.5). These values suggest a possible fundamental role of the electron-phonon interaction in the superconducting pairing mechanism.     

Electron-phonon coupling in cuprate and iron-based superconductors revealed by Raman scattering

Electron-phonon coupling （EPC） in cuprate and iron-based superconducting systems, as revealed by Raman scat- tering, is briefly reviewed. We introduce how to extract the coupling information through phonon lineshape. Then we discuss the strength of EPC in different high-temperature superconductor （HTSC） systems and possible factors affecting the strength. A comparative study between Raman phonon theories and experiments allows us to gain insight into some crucial electronic properties, especially superconductivity. Finally, we summarize and compare EPC in the two existing HTSC systems, and discuss what role it may play in the HTSC.