Influence Of Electron-phonon Interaction Research Articles

Diagrammatic method for the theory of magnetic and resistive properties of manganites

A diagrammatic method for the theory of magnetic and resistive properties of manganiteshas been applied. The Holstein double-exchange model for a narrow band with thestrong Hund’s rule coupling was studied. In parallel with the Lang–Firsov unitarytransformation of the zeroth Hamiltonian, we have realized the diagonalization of Hund’sHamiltonian neglecting the upper triplet. The diagram techniques taking intoaccount the quantum spin fluctuations of the lower quintet and hole state with spinS = 3/2 were developed. The magnetic structure of the ground state and an influence ofelectron–phonon interaction have been analysed using the first nonvanishing approximationof the perturbation theory. Since a simple self-consistent equation for the Green function islacking, the approximations for the effective interaction line with strong electron–phononcoupling were used. The influences of quantum fluctuations and electron–phononinteractions on magnetization, the Curie temperature and resistivity were investigated. Thecalculated temperature dependence of resistivity in the pure double-exchange model agreeswell with experimental data.

Polaronic Electron-Phonon Interactions on theThird-Harmonic Generation in a Square QuantumWell

The influence of electron-phonon interactionson third-harmonic generationin a square quantum well is investigated. The first- andthird-harmonic generation coefficient is obtained by usingcompact-density-matrix approach and iterative method, and thenumerical results are presented for a GaAs square quantum well.The results show that the third-harmonic generation coefficient isobviously enhanced after considering the influence of electron-phonon interactions.

Influence of electron-phonon interaction on single electron tunneling in a quantum dot molecule

The dynamics of electron tunneling between double quantum dots is investigated t heoretically in terms of a perturbation method based on a unitary transformation . Considering electron coupling with phonons, the dynamical tunneling current is obtained analytically. The phonon-induced decoherence is studied in detail. A possible decoupling mechanism is proposed.

Influence of electron-phonon interaction on the optical properties ofIII nitride semiconductors

The electronic band structures of III nitride semiconductors calculated withinthe adiabatic approximation give essential information about the opticalproperties of materials. However, atoms of the lattice are not at rest; theirdisplacement away from the equilibrium positions perturbs the periodicpotential acting on the electrons in the crystal, leading to anelectron-phonon interaction energy. Due to different ways that the latticevibration perturbs the motions of electrons, there are various types ofinteraction, such as Fröhlich interaction with longitudinal optical phonons,deformation-potential interactions with optical and acoustic phonons andpiezoelectric interaction with acoustic phonons. These interactions,especially the Fröhlich interaction, which is very strong due to the ionicnature of III nitrides, have a great influence on the optical properties ofthe III nitride semiconductors. As a result of electron-phonon interaction,several phenomena, such as phonon replicas in the emission spectra,homogeneous broadening of the excitonic line width and the relaxation ofhot carriers to the fundamental band edge, which have been observed in GaN andits low dimensional heterostructures, are reviewed.

Influence of electron-phonon interaction on spin-fluctuation-induced superconductivity

We investigate the interplay of the electron-phonon and the spin-fluctuation interaction in the superconducting state of ${\mathrm{YBa}}_{2}{\mathrm{Cu}}_{3}{\mathrm{O}}_{7}.$ The spin fluctuations are described within the nearly antiferromagnetic Fermi-liquid theory and the phonons are treated using a shell-model calculation of all phonon branches. The electron-phonon coupling is calculated using rigidly displaced ionic potentials screened by a background dielectric constant ${\ensuremath{\varepsilon}}_{\ensuremath{\infty}}$ and by holes within the ${\mathrm{CuO}}_{2}$ planes. We get a superconducting state with ${d}_{{x}^{2}\ensuremath{-}{y}^{2}}$ symmetry whose origin is antiferromagnetic spin fluctuations. The phononic contribution of all phonon modes of the system to the d-wave pairing interaction is attractive. This gives a positive isotope effect. The size of the isotope exponent depends strongly on the relative strength of the electron-phonon and spin-fluctuation coupling. Due to the strong electronic correlations no phononic induced superconducting state of s-wave character, is possible.

Conductivities of a quantum Hall system with a model disorder potential: Influence of electron-phonon interaction on plateau widths

We consider noninteracting electrons in a quasi-two-dimensional strip (extended in the $x$ direction) in the presence of a strong perpendicular magnetic field and a constant electric field in the $y$ direction, and subject to a model disorder potential $V(x,y)$ (``toy model'') which allows us to obtain the exact solutions of the time-dependent Schr\"odinger equation in very good approximation. Further, the electrons are coupled to a heat bath (accoustic phonons) at temperature $T$ that modifies the coherent Schr\"odinger time evolution induced by the electric field ${E}_{y}.$ After elimination of macroscopically unobservable fluctuations by averaging over suitable short time intervals, the time evolution that is relevant for the macroscopic current density can be described by a Boltzmann-type equation, which is solved numerically. The steady-state solution allows us to calculate ${\ensuremath{\sigma}}_{\mathrm{yy}}$ and ${\ensuremath{\sigma}}_{\mathrm{xy}}$ as a function of any physical parameter of the system. Here we give results of ${\ensuremath{\sigma}}_{\mathrm{yy}}$ and of ${\ensuremath{\sigma}}_{\mathrm{xy}}$ for all filling factors and as a function of temperature. Quantized Hall plateaus are obtained at the correct values with high precision. Between two plateaus, the Shubnikov--de Haas peak spreads out and its maximum decreases with increasing temperature in qualitative accordance with typical quantum Hall samples. Further, we obtain the remarkable result that for temperatures below 5 K the plateaus of ${\ensuremath{\sigma}}_{\mathrm{xy}}$ become sensibly larger than those of ${\ensuremath{\sigma}}_{\mathrm{yy}}.$ Our analysis shows that this effect results from electron-phonon interaction. (Such a phenomenon has been known experimentally for a long time, but it has seemed unexplained so far.) Our method of calculation could, in principle, be extended to more complex disorder potentials.

Influence of electron-phonon interaction on superexchange

We investigate the influence of electron-phonon coupling on the superexchange interaction of magnetic insulators. Both the Holstein-Hubbard model where the phonons couple to the electron density, as well as an extended Su, Schrieffer, Heeger model where the coupling arises from modulation of the overlap integral are studied using exact diagonalization and perturbative methods. In all cases for both the adiabatic (but non-zero frequency) and anti-adiabatic parameter regions the electron-phonon coupling is found to enhance the superexchange.

Influence of electron-phonon interaction to the periodic Anderson lattice

In heavy fermion compounds, the hybridization effect between the conduction and localized f-orbital electrons gives rise to a breathing phonon mode. This breathing mode couples with the conduction electrons and renormalizes the conduction bandwidth. Using the perturbation method for the one-dimensional periodic Anderson lattice, we study the influence of electron-phonon coupling on the hybridization effect and the stability of paramagnetic and antiferromagnetic states. Our results show that both the hybridization effect and Kondo temperature are reduced. This effect is more significant at large hybridization interaction in that it will destroy the stability of the antiferromagnetic state. However, this is already beyond the parameter ranges for the heavy fermion compounds.

Magnetic Excitation in Peierls-Hubbard Model

Based on the Peierls-Hubbard Hamiltonian, the influence of electron-phonon interaction on the spin excitation of itinerant systems has been analyzed. It is shown that the interaction not only changes the dynamic response properties, but also decreases the gap between two spin subbands, which makes the electron-hole pairs easy to be excited singly. It should be emphasized that the spin excitation spectrum has an energy gap due to the presence of the electron-phonon interaction mentioned above.

Optical processes of a single-atom model in the phonon field

The optical processes of a single-atom model in the phonon field have been studied. To deal with the quantum electrodynamics phenomena in condensed matter microcavities, the influence of electron-phonon interactions has to be taken into account. As a clear picture, the effect of the lattice's oscillation on the optical transition in condensed matter microcavities is reduced to a model of a single atom in a phonon field. We deduce that in the case with a phonon participating, the Bloch equation is still satisfied. In the process of spontaneous emission for an electron interacting with a phonon, we derive the Rabi oscillation for the simple atom in the phonon field.

INFLUENCE OF INTERACTION BETWEEN ELECTRONS AND PHONONS ON THE MAGNETIC EXCITATION OF ITINERANT ELECTRONS SYSTEM

Based on the Peierls-Hubbard Hamiltonian, the influence of electron-phonon inte-raction on the spin excitation of itinerant electron system has been analysed. It is shown that the interaction not only changes the dynamic property of －＋（ｑ，ω），but also causes the gap between two spin subbands to become narrow, which makes the electron-hole pairs easy to be excited singly. It should be emphasized that the spin excitation spectrum has an energy gap duo to the presence of above-mentioned electron-phonon interaction.

Influence of electron-phonon interactions on angle-resolved photoelectron spectra from metals

The influence of temperature on angle-resolved valence-band photoemission spectra from metals is not well understood. Despite considerable progress in recent years, both experimentally and theoretically, there is no profound understanding of how the electron-phonon coupling enters the experimental data. We present an improved description of temperature effects as revealed in peak intensities and line-widths. The basic constituent of this model is the incorporation of emission and absorption of phonons by the photoelectron. It has been applied to recent high-resolution data from bulk transitions in copper and a promising agreement could be obtained.

Polaron Effects on the Stark Shift of a Bound Polaron in Finite Quantum Wells

With both LO and SO modes being taken into account, the influence of electron-phonon interaction on QCSE of a bound polaron in a finite quantum well (QW) is investigated by means of the perturbation-variation method. It is found that the presence of an ionized impurity decreases the energy shift and weakens the effect of a finite barrier height. LO and SO mode effects will give significant corrections to the Stark energy shift individually and their influences on the shift just are contrary.

Influence of Electron-Phonon Interactions on the Physical Properties of an Interface Polaron11The project partly supported by National Natural Science Foundation of China through Grant No. 39188006.

Taking into account the interactions of both bulk longitudinal optical (LO) phonons and surface optical (SO) phonons and using Haga's perturbation method, we derive an effective Hamiltonian for the interface magnetopolaron in polar crystals at zero temperature. We illustrate in details how to solve this effective Hamiltonian analytically and we obtain explicit formulae not on1y for the electron cyclotron mass associated with the Landau levels but also for the self-trapping energy of the magnetopolaron with respect to its first three quantum states in the direction normal to the interface of the system. Numerical results are calculated for some II-V and III-V semiconductor compounds, indicating that the bulk LO phonons and SO phonons do have different trends of effects on the electron in different quantum states.

Polaron effects on the Stark shift of a bound polaron in infinite quantum wells

With both longitudinal optical (LO) and surface optical (SO) modes included, the influence of electron-phonon interactions on the quantum confined Stark effect in quantum wells is investigated by means of the variational technique. For an infinite GaAs-GaAlAs quantum well with a shallow donor located at its centre and subjected to an external electric field, the energy shifts of a conduction electron are calculated approximately. It is found that the presence of an ionized impurity decreases the energy shift. The LO mode and SO mode effect will give significant corrections to the Stark energy shift individually and their influences on the shift are just opposed.

Influence of electron-phonon interaction on the motion of an electron in a one-dimensional molecular system

Influence of electron-phonon interaction on the motion of an electron in a one-dimensional molecular system

Structural and electronic reconstructions in adsorbed layer

Abstract The influence of electron-phonon interaction on structural and electronic reconstructions of the ground state is considered for the system of adsorbed atoms on the metal surface. The consideration of this interaction is shown to result in a qualitative change of the reconstructions character with the doubling of the period of the two-dimensional lattice of adsorbed atoms (adatoms) at sufficiently strong electron-phonon interaction. These transitions are accompanied by both hop-like and smooth change of the effective charge of adatoms and their equilibrium positions; yhey can occur even at arbitrary weak interaction between adatoms. The structure with the doubled period is also shown to be unstable with respect to the formation of a long-wave superstructure, incommensurable with the lattice period of adatoms. The applicability of the model is discussed for the explanation of experimentally observed transitions on clean surfaces of transition metals.

Influence of electron-phonon interaction in doped silicon crystals on the root-mean-square dynamic displacement of atoms

The root-mean-square dynamic displacements (\(\begin{array}{*{20}c} -- \\ {u^2 } \\ \end{array} _{dyn} \)) of silicon atoms in single-crystals doped with phosphorus, arsenic, antimony, boron, gallium, and indium are determined experimentally. Characteristic concentration dependences of\(\begin{array}{*{20}c} -- \\ {u^2 } \\ \end{array} _{dyn} \) are obtained for boron- and phosphorus-doped silicon. A number of experimental facts indicating the existence of electron-phonon interaction in comparison with results in the literature, which are the results of an investigation of the same phenomenon by other methods, is discussed.

On the deformation potential constant of the conduction band in InSb

AbstractAn analysis of experimental data for InSb is made and the deformation potential constant ϵ1 of the conduction band is determined. It is shown that the correctly calculated value of |ϵ1| is about 30 eV. In the calculations of the carrier mobility for heavily doped semiconductors it is essential to take into account the effect of the band nonparabolicity on the transition probabilities and the screening of the scattering potentials by conduction electrons, and additionally at high temperatures it is necessary to consider the influence of electronphonon interaction on the effective mass and energy gap. The small values of |ϵ1| reported by some authors, who studied transport phenomena at low temperatures, are obtained under the condition ħ/τ > kBT (τ is the time between successive collisions), i.e. when the theory used is invalid.

The influence of dielectric properties on the emission of a metal-dielectric-metal system: Elastic scattering, optical phonons

The influence of electron-phonon interactions in a dielectric on the emission current and the transfer ratioα is investigated. A simple model of a thin-film field cathode, based on the tunnel effect between the first metal and the dielectric, has been proposed for this purpose. In the dielectric the tunnelling electrons can lose energy by collisions with phonons and flaws, and in the top electrode by collisions with electrons of metal 2. After some simplifications the transfer ratio α is obtained. The expressions forα are then discussed and compared with other models. It is shown that if the appropriate parameters are chosen for the cathode, the effect of the phonons will be negligible.