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 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 interaction and phonon conductivity in Li-doped silicon with intermediate donor concentration

Phonon conductivity in intermediately doped n-type silicon still remains unexplained. In this paper we have calculated the phonon conductivity in Li-doped silicon for N_ex < N_c using Mikoshiba's inhomogeneity model. We have introduced spherical polar coordinates for the phonon polarization vectors in Sota and Suzuki's theory in order to take into account the realistic picture of the scattered phonons. Deformation potential for different polarizations λ has been evaluated for the metallic region. Present calculations show that Mikoshiba's inhomogeneity model is able to explain the phonon conductivity of Li-doped silicon having intermediate donor concentration very well. Received 18 May 2001 / Received in final form 4 July 2002 Published online 19 December 2002 RID="a" ID="a"e-mail: mkroy@ctgu.edu     

Electron-phonon coupling spectrum in photodoped pentacene crystals

The coupling between conduction charges and the vibrational modes of the molecular lattice plays a defining role in the transport characteristics of organic semiconductors. Using electron tunneling spectroscopy, we obtain the electron--optical-phonon coupling spectrum in photodoped pentacene crystals at energies <30 meV. Comparison of the tunneling spectrum to infrared absorption data on the optical phonon density of states yields the energy dependence of the electron-phonon scattering matrix element. The integrated spectral weight of the electron-phonon coupling shows that superconductivity in pentacene is likely of electron-phonon origin.     

Electron-optical phonon coupling in superconductors

We investigate the role of the optical phonons in superconductivity in the case of compounds with different atomic massesM _k . We show that the electron mass enhancement factor is independent ofM _k if the force constant matrix is mass independent. However, when using to calculateT _c , it must be decomposed into its acoustical and optical contributions, which depend separately onM _k . We study interference scattering from a light and a heavy mass and its contributions to within the free electron approximation. Numerical results are presented for a rocksalt structure crystal with nearest and next nearest neighbour coupling. These results indicate that the optical phonon contributions to may substantially increaseT _c .Address after August 1975: Institut für Angew. Kernphysik, Kernforschungszentrum, 75 Karlsruhe, Germany     

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.     

纳米晶锐钛矿相TiO2的非简谐效应和声子局域

对晶粒尺寸为19.4,8.6和5.6 nm的纳米晶锐钛矿相TiO2,进行了从83到723 K的变温拉曼散射测量,并对Eg(1)模式进行了详细研究.根据非简谐效应和声子局域模型,对Eg(1)拉曼峰进行了拟合与计算.结果表明,以上三种纳米晶粒的晶格振动机理,在本质上是相同的.三声子过程对频率蓝移起主要作用.为了得到很好的拟合,需要同时考虑三声子和四声子过程.随着温度的升高,四声子过程增强,并对三声子过程起抵消作用.与非简谐衰减相关的声子寿命随着晶粒尺寸的减小而增加,晶粒尺寸越小衰减越慢.在低温区,声子局域是导致5.6 nm晶粒的声子寿命非常短的原因.声子局域引起Eg(1)模式在高波数段非对称展宽和频率蓝移,其对Eg(1)峰展宽的影响要大于对峰位移动的影响.     

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 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 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.     

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.     

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.     

纳米晶锐钛矿相TiO2的非简谐效应和声子局域

对晶粒尺寸为194,86和56nm的纳米晶锐钛矿相TiO₂,进行了从83到723K的变温拉曼散射测量,并对E_g(1)模式进行了详细研究.根据非简谐效应和声子局域模型,对E_g(1)拉曼峰进行了拟合与计算.结果表明,以上三种纳米晶粒的晶格振动机理,在本质上是相同的.三声子过程对频率蓝移起主要作用.为了得到很好的拟合,需要同时考虑三声子和四声子过程.随着温度的升高,四声子过程增强,并对三声子过程起抵消作用.与非简谐衰减相关的声子寿命随着晶粒 关键词： 2')" href="#">纳米晶TiO₂ 拉曼散射 非简谐耦合 声子局域