共查询到20条相似文献,搜索用时 297 毫秒
1.
J. Seebeck T. R. Nielsen P. Gartner F. Jahnke 《The European Physical Journal B - Condensed Matter and Complex Systems》2006,49(2):167-170
A microscopic theory for the interaction of carriers with LO phonons
is used to study the ultrafast carrier dynamics in nitride-based
semiconductor quantum dots. It is shown that the efficiency of
scattering processes is directly linked to quasi-particle
renormalizations. The electronic states of the interacting system are
strongly modified by the combined influence of quantum confinement and
polar coupling. Inherent electrostatic fields, typical for InGaN/GaN
quantum dots, do not limit the fast scattering channels. 相似文献
2.
D. Steiauf 《Journal of magnetism and magnetic materials》2010,322(6):L5
By making use of Kramer's degeneracy of the electronic states in a nonmagnetic material, Yafet has derived an expression for the spin relaxation time T1 due to scattering of electrons at phonons which involves the properties of electronic and phononic states and the matrix elements for the scattering. It is shown that an analogous expression for T1 can be derived for ferromagnets (where Kramer's degeneracy does not hold) when taking into account the conservation of the total number of electrons. This expression can be used as a starting point for the ab initio calculation of T1, and this quantity is required for an interpretation of the ultrafast demagnetization of ferromagnets after excitation with a femtosecond laser pulse. 相似文献
3.
We study light absorption mechanisms in semiconducting carbon nanotubes using low-temperature, single-nanotube photoluminescence excitation spectroscopy. In addition to purely electronic transitions, we observe several strong phonon-assisted bands due to excitation of one or more phonon modes together with the first electronic state. In contrast with a small width of emission lines (sub-meV to a few meV), most of the photoluminescence excitation features have significant linewidths of tens of meV. All of these observations indicate very strong electron-phonon coupling that allows efficient excitation of electronic states via phonon-assisted processes and leads to ultrafast intraband relaxation due to inelastic electron-phonon scattering. 相似文献
4.
基于静电-交换和密耦合两种模型,采用R矩阵方法,研究了低能电子与二氧化氮自由基分子的积分散射截面和动量迁移散射截面,包括弹性散射和从电子基态到电子激发态的非弹性散射.采用aug-cc-pVTZ基组进行靶分子结构优化和散射研究.在密耦合模型中,包含6个电子的最低三个占据轨道1b_2,1a_1,2a_1被冻结,其余17个电子自由运动在活化空间中,并给活化空间增加了2b_1和7a_1两个虚轨道.包含了所有垂直激发能小于20 eV的靶分子电子组态,得到了收敛的散射截面,并与最新理论和实验值进行了比较.当入射能量小于4 eV时,本文结果与实验值符合得更好,校正了以往部分理论结果在极低能量处过高的现象,表明关联效应对于极低能量散射是非常重要的. 相似文献
5.
Tunnelling electrons may scatter inelastically with an adsorbate, releasing part of their energy
through the excitation of molecular vibrations. The resolution of inelastic processes with a low
temperature scanning tunnelling microscope (STM) provides a valuable tool to chemically
characterize single adsorbates and their adsorption mechanisms. Here, we present a molecular scale
picture of single molecule vibrational chemistry, as resolved by STM. To understand the way a
reaction proceed it is needed knowledge about both the excitation and damping of a molecular
vibration. The excitation is mediated by the specific coupling between electronic molecular
resonances present at the Fermi level and vibrational states of the adsorbate. Thus, the
two-dimensional mapping of the inelastic signal with an STM provides the spatial distribution of
the adsorbate electronic states (near the Fermi level) which are predominantly coupled to the
particular vibrational mode observed. The damping of the vibration follows a competition between
different mechanisms, mediated via the creation of electron-hole pairs or via anharmonic coupling
between vibrational states. This latter case give rise to effective energy transfer mechanisms
which eventually may focus vibrational energy in a specific reaction coordinate. In this
single-molecule work-bench, STM provides alternative tools to understand reactivity in the limit of
low excitation rate, which demonstrate the existence of state-specific excitation strategies which
may lead to selectivity in the product of a reaction. 相似文献
6.
稀土固体是重要的激光和光电子材料。目前,由于以宽带信号和太赫兹比特数据传输率为特征的信息技术的发展,稀土固体材料的相干瞬态动力学过程成为宽带与高速信息光子学的基本物理问题之一。研究了室温下稀土粉末样品Eu3+:Y2O3自由感应衰减的相干瞬态光谱,这有助于理解有效的光吸收动力学、激发态弛豫、相干能量传递和超短光脉冲在稀土固体中的传播。用一对紫外飞秒相干光脉冲作用于稀土粉末样品Eu3+:Y2O3,然后监测物质激发态的布居数随两个激发脉冲之间的延时的变化,测量到其自由感应衰减量子拍(FID),从拍频周期分析确定了其能级精细结构,能级的退相时间长达皮秒量级。理论分析和实验结果符合得很好。对稀土离子的量子干涉的研究,表明其在受激受控光放大方面具有潜在的应用前景。 相似文献
7.
G. Rohde T. Rohwer C. Sohrt A. Stange S. Hellmann L. X. Yang K. Hanff A. Carr M. M. Murnane H. Kapteyn L. Kipp K. Rossnagel M. Bauer 《The European physical journal. Special topics》2013,222(5):997-1004
The ultrafast dynamics of excited electrons in 1T-TiSe2 after absorption of a 390 nm light pulse is probed by time- and angle-resolved photoemission spectroscopy using femtosecond XUV pulses. It is demonstrated that the experimental approach can provide a comprehensive view of hot carrier motion in momentum space during relaxation back to equilibrium. This capability opens a new avenue in the investigation of energy dissipation processes in solids after intense optical excitation. 相似文献
8.
A. Perali M. Sindel G. Kotliar 《The European Physical Journal B - Condensed Matter and Complex Systems》2001,24(4):487-503
A number of normal state transport properties of cuprate superconductors are analyzed in detail using the Boltzmann equation.
The momentum dependence of the electronic structure and the strong momentum anisotropy of the electronic scattering are included
in a phenomenological way via a multi-patch model. The Brillouin zone and the Fermi surface are divided in regions where scattering between the electrons
is strong and the Fermi velocity is low (hot patches) and in regions where the scattering is weak and the Fermi velocity is
large (cold patches). We present several motivations for this phenomenology starting from various microscopic approaches.
A solution of the Boltzmann equation in the case of N patches is obtained and an expression for the distribution function away from equilibrium is given. Within this framework,
and limiting our analysis to the two patches case, the temperature dependence of resistivity, thermoelectric power, Hall angle,
magnetoresistance and thermal Hall conductivity are studied in a systematic way analyzing the role of the patch geometry and
the temperature dependence of the scattering rates. In the case of Bi-based cuprates, using ARPES data for the electronic
structure, and assuming an inter-patch scattering between hot and cold states with a linear temperature dependence, a reasonable
agreement with the available experiments is obtained.
Received 3 August 2001 and Received in final form 1st November 2001 相似文献
9.
Albert Schmid 《Zeitschrift für Physik A Hadrons and Nuclei》1974,271(3):251-256
The inelastic scattering of the electrons of an impure metal by a screened Coulomb interaction is investigated. It is found that the rate of such an inelastic scattering is increased which can be explained by a loss of momentum conservation which in turn results from loss of translational symmetry introduced by the defects of an impure metal. Eventually, a linearised Boltzmann equation is derived for time and space dependent perturbances of the electronic distribution function. The collision integral takes into account impurity scattering as well as electron-electron and electron-phonon scattering. In an impure metal the terms corresponding to the last two processes are modified as discussed above and in a previous paper on the electron-phonon interaction. 相似文献
10.
Excited electrons at surfaces can be scattered by adsorbate atoms or defects, which changes the energy or momentum. Such scattering
processes can be studied by energy, time and angle-resolved two-photon photoelectron spectroscopy. In this article the influence
of statistically distributed Co adatoms on a Cu(001) surface on the dynamics of electrons in image-potential states is investigated.
Different scattering mechanisms, such as interband, intraband, and bulk scattering are identified and analyzed quantitatively.
Cobalt adatoms cause mainly quasielastic scattering of electrons in image-potential states. Inelastic processes are due to
interactions with electrons in the substrate and are not significantly increased by Co adatoms. The results are compared to
previous experimental and theoretical work on Cu adatoms.
PACS 73.20.At; 68.49.Jk; 79.60.Ht 相似文献
11.
Modeling of Nonthermal Solid‐to‐Solid Phase Transition in Diamond Irradiated with Femtosecond x‐ray FEL Pulse 下载免费PDF全文
In this contribution we review in detail our recently developed hybrid model able to trace simultaneously nonequilibrium electron kinetics, evolution of an electronic structure, and eventually nonthermal phase transition in solids irradiated with femtosecond free‐electron laser pulses. Diamond irradiated with an ultrashort intense x‐ray pulse serves as an example to show how an irradiated material undergoes an ultrafast phase transition on sub‐picosecond timescales. The transition of diamond into graphite is induced by an excitation of electrons from the valence band into the conduction band, which, in turn, induces a rapid change of the interatomic potential. Our theoretical model incorporates: a Monte‐Carlo method for tracing high‐energy electrons and K‐shell holes in diamond; a temperature equation for the valence‐band and low‐energy conduction‐band electrons; a tight binding method for calculation of the evolving electronic structure of the material and potential energy surfaces; and molecular dynamics propagating atomic trajectories. This unified approach predicts the damage threshold of diamond in a good agreement with experimentally measured values. It reveals a multi‐step nature of nonthermal phase transition being an interplay between electronic excitation, changes of the band structure, and atomic reordering. An effect of pulse parameters, such as photon energy and temporal pulse shape, on the phase transition is discussed in detail. (© 2015 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
12.
In this paper, we present Raman spectra of ZrS2, HfS2, MoS2 and WS2 using laser energies near the energies of the absorption edges. The Raman spectra probe the properties of the first-excited electronic state and the nature of the electron-phonon coupling. The spectra of the IVB disulfides are independent of the laser excitation energy, suggesting weak electron-phonon interaction. In contrast, additional Raman bands appear in the spectra of the VIB disulfides as the laser energy approaches the band gap energy. The new modes in the spectra of MoS2 and WS2 cannot be assigned as first-order processes nor as combination bands of the phonons with zero momentum. The resonance Raman scattering of MoS2 is analyzed in terms of second-order scattering due to the coupling of phonon modes of nonzero momentum with an electronic transition associated with excitonic states. 相似文献
13.
14.
M. Combescot O. Betbeder-Matibet 《The European Physical Journal B - Condensed Matter and Complex Systems》2011,79(4):401-421
The final goal of this paper is to derive the effective scattering ruling the time evolution of two semiconductor trions using
the many-body formalism for composite fermions we have just proposed. However, to understand the importance of the particle
composite nature, their bosonic/fermionic character and their overall charge, we also report on scatterings between free electrons,
excitons and trions. This leads us to identify the form factors associated to direct processes involving excitons and trions.
For transitions between ground states, these form factors reduce to zero and one respectively, in the small momentum transfer
limit. 相似文献
15.
Ultra low momentum neutron catalyzed nuclear reactions in metallic hydride system surfaces are discussed. Weak interaction
catalysis initially occurs when neutrons (along with neutrinos) are produced from the protons that capture “heavy” electrons.
Surface electron masses are shifted upwards by localized condensed matter electromagnetic fields. Condensed matter quantum
electrodynamic processes may also shift the densities of final states, allowing an appreciable production of extremely low
momentum neutrons, which are thereby efficiently absorbed by nearby nuclei. No Coulomb barriers exist for the weak interaction
neutron production or other resulting catalytic processes.
PACS 24.60.-k, 23.20.Nx 相似文献
16.
We have examined the head-on collision of two electrons in the approximation of coherent states. We have shown that the character of the collision depends mainly on the ratio of the initial relative electron momentum to the momentum uncertainty of electrons. When this ratio becomes greater than 1, the Coulomb interaction practically does not influence the scattering. 相似文献
17.
L. Mayrhofer M. Grifoni 《The European Physical Journal B - Condensed Matter and Complex Systems》2008,63(1):43-58
The low energy spectrum of finite size metallic single-walled carbon nanotubes (SWNTs) is determined. Starting from a tight
binding model for the pz electrons, we derive the
low energy Hamiltonian containing all relevant scattering processes
resulting from the Coulomb interaction, including the short
ranged contributions becoming relevant for small diameter tubes. In
combination with the substructure of the underlying honeycomb lattice
the short ranged processes lead to various exchange effects. Using
bosonization the spectrum is determined. We find that the ground state
is formed by a spin 1 triplet, if 4n+2 electrons occupy the
SWNT and the branch mismatch is smaller than the exchange splitting.
Additionally, we calculate the excitation spectra for the different
charge states and find the lifting of spin-charge separation as well
as the formation of a quasi-continuum at higher excitation energies. 相似文献
18.
A. Amo D. Ballarini D. Sanvitto E. Kozhemyakina L. Via M.S. Skolnick J.S. Roberts 《Superlattices and Microstructures》2008,43(5-6):449
We present a time resolved experiment in which we dynamically tailor the occupation and temperature of a photogenerated exciton distribution in QWs by excitation with two delayed picosecond pulses. The modification of the excitonic distribution results in ultrafast changes in the PL dynamics. Our experimental results are well accounted by a quasiequilibrium thermodynamical model, which includes the occupation and momentum distribution of the excitons. We use this model and the two-pulse experimental technique to study the polariton dynamics in InGaAs-based microcavities in the strong coupling regime. In particular, we demonstrate that resonantly injected upper polaritons mainly relax to the lower polariton branch via scattering to large momentum polariton states, producing the warming of the polariton reservoir. 相似文献
19.
Surface localized electronic states constitute electronic environment for a variety of physical and chemical phenomena taking place on surfaces. Various processes of model catalytic reactions may be influenced or mediated by hot electrons and holes excited in quasi-two-dimensional bands occurring on a large number of metal surfaces. Here we discuss several important aspects of nonadiabatic dynamics of these excitations which may affect the measurements of surface electronic properties by ultrafast electron spectroscopies. 相似文献
20.
《中国物理快报》2021,(7)
We report an implementation of the momentum space quantum Monte Carlo(QMC) method on the interaction model for the twisted bilayer graphene(TBG). The long-range Coulomb repulsion is treated exactly with the flat bands, spin and valley degrees of freedom of electrons taking into account. We prove the absence of the minus sign problem for QMC simulation when either the two valleys or the two spin degrees of freedom are considered.By taking the realistic parameters of the twist angle and interlayer tunnelings into the simulation, we benchmark the QMC data with the exact band gap obtained at the chiral limit, to reveal the insulating ground states at the charge neutrality point(CNP). Then, with the exact Green's functions from QMC, we perform stochastic analytic continuation to obtain the first set of single-particle spectral function for the TBG model at CNP. Our momentum space QMC scheme therefore offers the controlled computation pathway for systematic investigation of the electronic states in realistic TBG model at various electron fillings. 相似文献