Free electron model

About: Free electron model is a research topic. Over the lifetime, 4678 publications have been published within this topic receiving 103535 citations.

Fermi Surface and Mass Enhancement in KFe2As2 from de Haas-van Alphen Effect Measurements

Abstract: We report on a band structure calculation and de Haas–van Alphen measurements of KFe 2 As 2 . Three cylindrical Fermi surfaces are found. Effective masses of electrons range from 6 to 18 m e , m e being the free electron mass. Remarkable discrepancies between the calculated and observed Fermi surface areas and the large mass enhancement (\({\gtrsim}3\)) highlight the importance of electronic correlations in determining the electronic structures of iron pnicitide superconductors.

Free electron properties of metals under ultrafast laser-induced electron-phonon nonequilibrium: a first-principles study

Abstract: The electronic behavior of various solid metals (Al, Ni, Cu, Au, Ti, and W) under ultrashort laser irradiation is investigated by means of density functional theory. Successive stages of extreme nonequilibrium on picosecond time scale impact the excited material properties in terms of optical coupling and transport characteristics. As these are generally modelled based on the free-electron classical theory, the free-electron number is a key parameter. However, this parameter remains unclearly defined and dependencies on the electronic temperature are not considered. Here, from first-principles calculations, density of states are obtained with respect to electronic temperatures varying from ${10}^{\ensuremath{-}2}$ to ${10}^{5}$ K within a cold lattice. Based on the concept of localized or delocalized electronic states, temperature dependent free-electron numbers are evaluated for a series of metals covering a large range of electronic configurations. With the increase of the electronic temperature we observe strong adjustments of the electronic structures of transition metals. These are related to variations of electronic occupation in localized $d$ bands, via change in electronic screening and electron-ion effective potential. The electronic temperature dependence of nonequilibrium density of states has consequences on electronic chemical potentials, free-electron numbers, electronic heat capacities, and electronic pressures. Thus electronic thermodynamic properties are computed and discussed, serving as a base to derive energetic and transport properties allowing the description of excitation and relaxation phenomena caused by rapid laser action.

Extracting reliable electronic properties from transmission spectra of indium tin oxide thin films and nanocrystal films by careful application of the Drude theory

Abstract: Analysis of the transmittance and reflectance of transparent conducting oxide thin films and nanocrystal films can be accurately modeled using the Drude free electron theory to extract electrical transport properties if enough care is taken. However, several fits starting from different initial guesses are needed before confidence in the extracted Drude parameters can be obtained. Film thickness, optical carrier concentration, and optical carrier mobility can be reliably derived when using either a fully empirical or semiempirical model for the ionized impurity scattering. The results are in good agreement with those based on more arduous spectroscopic ellipsometry measurements. Furthermore, fitting the reflectance along with the transmittance reduces the uncertainty, but does not significantly affect the values of the extracted parameters.

Analysis of Smith-Purcell free-electron lasers

Abstract: We present an analysis of the beam dynamics in a Smith-Purcell free-electron laser (FEL). In this system, an electron beam interacts resonantly with a copropagating surface electromagnetic mode near the grating surface. The surface mode arises as a singularity in the frequency dependence of the reflection matrix. Since the surface mode is confined very close to the grating surface, the interaction is significant only if the electrons are moving very close to the grating surface. The group velocity of the surface mode resonantly interacting with a low-energy electron beam is in the direction opposite to the electron beam. The Smith-Purcell FEL is therefore a backward wave oscillator in which, if the beam current exceeds a certain threshold known as start current, the optical intensity grows to saturation even if no mirrors are employed for feedback. We derive the coupled Maxwell-Lorentz equations for describing the interaction between the surface mode and the electron beam, starting from the slowly varying approximation and the singularity in the reflection matrix. In the linear regime, we derive an analytic expression for the start current and calculate the growth rate of optical power in time. The analysis is extended to the nonlinear regime by performing a one-dimensional time-dependent numerical simulation. Results of our numerical calculation compare well with the analytic calculation in the linear regime and show saturation behavior in the nonlinear regime. We find that a significant amount of power grows in the surface mode due to this interaction. Several ways to outcouple this power to freely propagating modes are discussed.

X-Ray Parametric Conversion

Abstract: The observation of x-ray parametric conversion is reported. Results are in accord with the calculated nonlinear x-ray susceptibility. The appropriate nonlinear mechanisms are described in terms of classical free electrons.