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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.


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TL;DR: In this paper, the authors examined relative stability and physical properties of several possible magnetic states in the mean field theory for an itinerant electron model, i.e., the Hubbard model on a two-dimensional square lattice.
Abstract: Spatially modulated magnetic phases are investigated within the mean field theory for an itinerant electron model, i.e. the Hubbard model on a two-dimensional square lattice. By numerically diagonalizing the Hamiltonian for finite-size systems under a periodic boundary condition, we examine relative stability and physical properties of several possible magnetic states. When the electron fillings are nearly half-full, the diagonally or vertically modulated spin density wave (SDW) state is stabilized over the uniform antiferromagnetic state and a crossover from the vertical to the diagonal states appears. The diagonal or vertical stripe state is characterized by the presence of the midgap band due to the soliton lattice formation inside the main SDW gap, being an insulator. The wave length λ SDW is linearly proportional to the excess carrier concentration. Excess carriers are accommodated in the form of the soliton lattice, forming a charge density wave whose wave length is λ SDW /2.

194 citations

Journal ArticleDOI
TL;DR: In this paper, free and trapped charge carriers in polycrystalline TiO2 following band gap irradiation are characterized by diffuse reflectance IR spectroscopy (DRIFTS), indicating the presence of free conduction band electrons coupled with acoustic phonons in the lattice.
Abstract: Free and trapped charge carriers in polycrystalline TiO2 following band gap irradiation are characterized by diffuse reflectance IR spectroscopy (DRIFTS). A spectrum-wide absorption signal proportional to λ1.7 (λ = wavelength/μm) indicates the presence of free conduction band electrons coupled with acoustic phonons in the lattice. Free electrons appear to decay according to saturation kinetics. The fitted parameters indicate a limited number of trapping states. The concentration of these states appears to be diminished by sequential UV treatments. The free carrier decay lifetime is lengthened as the samples are dehydrated, which suggests an excited-state relaxation event during electron trapping. Photogenerated free electrons are comparable to conduction band electrons injected from surface-bound chromophores, and the lifetime of these electrons can be extended across several orders of magnitude. A broad IR absorption peak centered at 3380 cm-1 is attributed to an electronic transition from an occupied su...

192 citations

Book
01 Jan 1971
TL;DR: In this paper, the authors proposed a theory of infra-red dispersion in a crystal lattice, and showed that the theory can be used to describe a wide range of non-linear effects.
Abstract: 1. Macroscopic Theory.- 1.1 Electromagnetic field in a solid.- 1.2 Dielectric constant and optical conductivity.- 1.3 Crystal symmetry.- 1.4 Propagation of waves.- 1.5 Kramers-Kronig relations.- 1.6 The sum rule.- 1.7 Dispersion theory of classical oscillators.- 2. Crystal Lattice Absorption.- 2.1 Vibrational modes of a crystal lattice.- 2.2 Photon-phonon interaction.- 2.3 Microscopic theory of infra-red dispersion.- 2.4 Two-phonon absorption.- 3. Interband Transitions.- 3.1 Electron energy bands.- 3.2 Direct transitions.- 3.3 Critical points.- 3.4 Absorption band edges.- 3.5 Indirect transitions.- 3.6 Infra-red absorption in superconductors.- 4. Free Carrier Absorption.- 4.1 Classical theory.- 4.2 Intraband transitions.- 4.3 Electron transport.- 4.4 Surface admittance.- 4.5 Infra-red absorption in metals.- 4.6 Free carrier absorption in semiconductors.- 5. Plasma Effects.- 5.1 Free electron model.- 5.2 Volume plasmons.- 5.3 Surface plasmons.- 6. Exciton Effects.- 6.1 Electron-hole interaction.- 6.2 Optical absorption.- 6.3 Inert-atom solids and alkali halides.- 6.4 Semiconductors.- 6.5 Spatial dispersion.- 7. Non-Linear Optics.- 7.1 Classification of non-linear effects.- 7.2 Non-linear susceptibilities.- 7.3 Second harmonic generation.- 7.4 Parametric amplification and oscillation.- 7.5 Third order effects.- References.

184 citations

Journal ArticleDOI
25 Jul 2002-Nature
TL;DR: This experiment uses an electron field emitter to coherently illuminate two detectors, and finds anticorrelations in the arrival times of the free electrons, which represents the fermionic twin of the Hanbury Brown–Twiss effect for photons.
Abstract: Fluctuations in the counting rate of photons originating from uncorrelated point sources become, within the coherently illuminated area, slightly enhanced compared to a random sequence of classical particles. This phenomenon, known in astronomy as the Hanbury Brown-Twiss effect, is a consequence of quantum interference between two indistinguishable photons and Bose Einstein statistics. The latter require that the composite bosonic wavefunction is a symmetric superposition of the two possible paths. For fermions, the corresponding two-particle wavefunction is antisymmetric: this excludes overlapping wave trains, which are forbidden by the Pauli exclusion principle. Here we use an electron field emitter to coherently illuminate two detectors, and find anticorrelations in the arrival times of the free electrons. The particle beam has low degeneracy (about 10(-4) electrons per cell in phase space); as such, our experiment represents the fermionic twin of the Hanbury Brown-Twiss effect for photons.

183 citations

Journal ArticleDOI
TL;DR: In this paper, a stability criterion was derived for the localization of an excess electron in a dense fluid of nonpolar molecules, expressed in terms of a relation between the energy of the quasifree electron state and the bubble surface energy.
Abstract: In this paper we consider the properties of an excess electron in the nonpolar dense fluids 3He, 4He, Ne, Ar, and H2. The energy of the quasifree electron state was estimated through the use of an approximate polarization potential and of pseudopotential theory, together with average Wigner–Seitz boundary conditions. The Wigner–Seitz approximation was also applied to the study of the localized state. A stability criterion was derived for the localization of an excess electron in a dense fluid of nonpolar molecules. The stability criterion is expressed in terms of a relation between the energy of the quasifree electron state and the bubble surface energy. Three cases of physical interest which can be distinguished are those of the existence of a quasifree state, the existence of a metastable bubble, and the formation of an energetically stable bubble. The stability criterion predicts that excess electron states in liquid He and in liquid He, should be localized, the excess electron state in liquid Ar should be quasifree, while liquid neon provides a borderline case between the stable and the metastable bubble. The available experimental data concerning the energy barrier for adiabatic electron injection and electron mobilities in liquid He, liquid H2, and liquid Ar are consistent with the results of the present treatment.

183 citations


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Performance
Metrics
No. of papers in the topic in previous years
YearPapers
202340
202290
2021132
2020122
2019114
2018112