Matrix Elements Of Electron-phonon Interaction Research Articles

Electron-phonon scattering limited hole mobility at room temperature in a MoS2 monolayer: first-principles calculations.

Based on first-principles calculations and iterative solution of the Boltzmann transport equation, we theoretically study the room temperature mobility (RTM) of a valence band hole in a MoS2 monolayer (ML) limited by electron-phonon (e-ph) scattering. The hole mobility obtained by us is 26.0 cm2 V-1 s-1 at 300 K. This is a value much closer to the experimental result (about 40.0 cm2 V-1 s-1). In contrast, the semi-empirical estimate based on the deformational potential (DP) model in previous literature gave a value of 200.5 cm2 V-1 s-1, far away from the experimental data. By a detailed analysis, we find that unlike the case of conduction band electrons, the intervalley scattering realized by longitudinal acoustic (LA) phonons plays a dominant role in influencing the hole mobility. And this is the main reason for the DP model failing to give a quantitative estimate of the hole RTM in MoS2-ML.

A PROPOSED NEW MEASUREMENT OF THE SUPERCONDUCTING GAP IN YBa2Cu3O7

The superconducting energy gap of YBa 2 Cu 3 O 7 (YBCO) varies strongly with [Formula: see text] and from a sheet of the Fermi surface to another. The strong anisotropic superconducting gap in high Tc materials such as YBCO has led to conflicting d-wave and s-wave interpretations. We have utilized electronic wave functions from the ab-initio density functional calculation and the related electron-phonon interaction matrix elements for the calculation of the superconducting gap values of YBCO. We have found that the superconducting gap on one sheet of the Fermi surface around S-point only shows a minor variation from about 18 meV to 25 meV. Especially, there is no node on this sheet of the Fermi surface around the S-point. We propose a new test measurement of the superconducting gap of YBCO on this sheet of the Fermi surface around the S-point in the Brillouin zone. This measurement is expected to shed light on the gap symmetry properties of high Tc superconductors.

Electron-phonon interaction and its influence on reconstruction of single-walled carbon nanotube radial breathing mode spectra

The relative electron-phonon interaction matrix elements (Mph) for 28 (n,m) semiconducting single walled carbon nanotubes (SWNTs) species were extracted from the resonance Raman cross sections of individually dispersed high-pressure CO SWNTs. The observed Mph pattern was fitted according to nanotube family [i.e., (2n+m)=const] and modality [i.e., mod(n−m,3)=1, or 2] using an empirical equation based on trigonal warping effects. The predicted Mph trends enabled significant improvement to the reconstruction of the radial breathing mode spectra, so that a better match was obtained to the experimental spectra for both dispersed and aggregated SWNTs. The latter provides an initial indication that the observed Mph trends are preserved during aggregation.

Effective Hamiltonian for HTSC cuprates taking into account electron-phonon interaction in the strong-correlation regime

Electron-phonon interaction is sequentially derived from a realistic p-d multiband model for the cuprates under conditions of strong electron correlations. The electronic structure is described using the representation of the Hubbard X operators in a generalized tight-binding method. Dependences of the diagonal and off-diagonal (on lattice sites) matrix elements of electron-phonon interaction on the wavevectors are found for three phonon modes, namely, breathing, apical breathing, and bending modes. The interactions of the breathing and bending modes with electrons are shown to contribute to the formation of kinks in the (0; 0)-(π; π) and (0; 0)-(π; 0) directions, respectively. A low-energy t-J* model with phonons is developed; apart from electron-phonon interaction, it also includes spin-phonon interaction. The elimination of phonons gives an effective electron-electron interaction that depends on the occupation number of a multielectron term and on the carrier concentration due to strong electron correlations.

The Gap Function in YBa2Cu3O7

We have solved the four-dimensional anisotropic Eliashberg gap equation for YBa2Cu3O7 (YBCO) using the calculated electronic structure and the electron–phonon interaction matrix elements. The calculated T c for YBCO is about 89 K or μ*= 0.1. At or slightly above the transition temperature T c , the real part of the gap function Δ(k, 0), for all the k-points on the Fermi surface, becomes zero and the material is not superconducting. However, the energy gap function Δ(k,ω) is still nonzero for ω > 0 for some electronic states, leading to a pseudo-gap behavior in YBCO.

Interaction between electronic and phonon Raman scattering in hole space charge layers on silicon

The interaction of quasi-continuous electronic excitations in hole space charge layers of Si with the optical phonons is investigated. The induced asymmetric broadening of the one-phonon line can be understood as a quantum mechanical interference of the continuum excitations with the discrete energy state. The lineschape is directly related to electron-phonon interaction matrix elements.

Study of electron–phonon interaction in nickel and iron by microcontact spectroscopy

Microcontact spectroscopy is used to obtain the electron–phonon interaction spectra of the ferromagnetic metals nickel and iron. The data obtained are compared to known phonon state density functions F(ω). The mean squares of the electron–phonon interaction matrix elements are calculated as functions of energy. The presence in the experiments of a “structural” broadening connected with imperfection of the metal structure in the microcontact region is noted.

Generalisation of the Frohlich-Mitra modified tight-binding approximation toward the description of the electron-phonon coupling in solids

In order to describe the electron motion in deformed lattices, the Frohlich-Mitra modified tight-binding approximation (1968) has been generalised. The unperturbed electronic wavefunction is written as a Bloch sum of displaced and suitably orthonormalised Wannier functions so as to take partly into account the adiabatic followup of the electron upon deformation of the lattice. It is then shown that the electron-phonon interaction matrix elements in this scheme are identical with those given by the ordinary Bloch theory.

Interpolation-Scheme Calculation of Electron-Phonon Interaction in Noble and Transition Metals: Copper

A simple method for evaluating the electron-phonon interaction matrix elements, and hence the point-mass enhancement and the relaxation time of quasiparticles, is proposed for the transition metals. The method is based essentially on the Bloch model of the electron-phonon interactions and is similar to a pseudopotential formulation with modification to account for the presence of $d$ electrons in the conduction bands and the resulting anisotropy of the above quantities. The results obtained by applying our theory to copper, based on the combined interpolation scheme with explicit inclusion of the screening effects based on Lindhard's formulation and of the contributions from transverse and longitudinal phonons and from umklapp processes, are in fair quantitative agreement with those obtained from a phenomenological interpretation of the experimental cyclotron-mass data of Lee and with the calculations of Nowak based on an empirical phase-shift formulation.