Showing papers on "Brillouin zone published in 1986"
TL;DR: The first observation of the modulational instability of light waves in dielectric material using a neodymium-doped yttrium aluminum garnet laser operated at 1.319 \ensuremath{\mu}m and single-mode optical fibers with anomalous group-velocity dispersion is reported.
Abstract: We report the first observation of the modulational instability of light waves in dielectric material using a neodymium-doped yttrium aluminum garnet laser operated at 1.319 \ensuremath{\mu}m and single-mode optical fibers with anomalous group-velocity dispersion. The observed results are in good agreement with the theoretical predictions. The relationship between the modulation instability and parametric four-wave mixing and the interplay with stimulated Raman and Brillouin scatterings are also presented.
712 citations
TL;DR: Single-photon- and multiphoton-induced luminescence spectra were obtained from clean samples of silver, copper, and gold with both smooth and rough surfaces and reveal new features which are correlated with interband transitions at selected symmetry points in the Brillouin zone.
Abstract: Single-photon- and multiphoton-induced luminescence spectra were obtained from clean samples of silver, copper, and gold with both smooth and rough surfaces. The spectra reveal new features which are correlated with interband transitions at selected symmetry points in the Brillouin zone. Calculating luminescence spectra based on simplified models of the band structures of the noble metals and taking into account the Fresnel local-field corrections, we find qualitative agreement with the observed spectra from smooth samples. The agreement between theory and experiment is less satisfactory for rough samples. The influence of surface roughness on the luminescence is largely attributable to local-field enhancement in the rough surface protrusions.
703 citations
IBM1
TL;DR: In this article, the authors explain the unusual corrugations observed in scanning-tunneling-microscope (STM) images of 1 T-TaS2, Si(111), 2 × 1, and graphite.
Abstract: Unusual corrugations observed in scanning-tunneling-microscope (STM) images of 1 T-TaS2, Si(111)(2 × 1), and graphite are explained, and are shown to be characteristic of materials where the Fermi surface has collapsed to a point at the corner of the surface Brillouin zone. This is the first clear case where the low-bias STM image is dominated by electronic structure effects rather than surface geometry. Implications for STM spatial resolution are discussed.
149 citations
TL;DR: In this paper, a new technique called picosecond interferometry is proposed for the study of phonons in the Brillouin frequency range in transparent materials, which makes possible the measurement of longitudinal phonon velocity and attenuation under conditions such that the conventional approach is not applicable.
144 citations
TL;DR: It is observed that the twofold degeneracy of plasmon modes with wave numbers in the first Brillouin zone of the infinite system is lifted by the loss of complete periodicity in the finite system.
Abstract: We observe discrete plasmons in layered 2D electron gases with a large, but finte, number of periods. The twofold degeneracy of plasmon modes with wave numbers in the first Brillouin zone of the infinite system is lifted by the loss of complete periodicity in the finite system. These characteristic discrete plasmon doublets are measured in inelastic-light-scattering spectra of multilayer GaAs/(AlGa)As heterostructures.
101 citations
TL;DR: In this paper, a set of special points in numerical integrations over Brillouin zones (BZ) is given for the five two-dimensional Bravais lattices, which coincide with a special case of the large unit cell (LUC) method.
Abstract: A clear tabulation of sets of special points in numerical integrations over Brillouin zones (BZ) is given for the five two-dimensional Bravais lattices. The special points derived on the basis of plain geometrical criteria coincide with a special case of the large unit cell (LUC) method. This similarity is also found for other generation procedures of k-grids reported in the literature; that is, the corresponding techniques have their common origin in the LUC approach. The underlying integration procedure of the described scheme is based on the discrete summation, which implies that the weighting factors at the k-points are only determined by the point symmetry in reciprocal space not by details of the adopted numerical integration formalism. The method can be applied to semiconducting and insulating solids—that is, to materials with finite band gaps. Grids in reciprocal space are generated on the basis of simple geometric criteria. The numerical effort of the present geometrical approach is negligible in comparison to the computational steps necessary in generation procedures of optimized k-grids that have been published in the literature. The application of the suggested integration procedure is extremely simple; the generation of the k-grids is only based on a few definitions and plain geometrical formulas. Modifications of the grid size are possible without difficulties. A collection of weighting factors ωi and special and general positions in the BZ is given; different grids are tabulated together with their geometrical efficiencies. The generated integration domains are compared with the results of elaborate schemes of finding grids with maximal efficiency.
91 citations
TL;DR: In this article, the authors presented calculations of the lifetime broadenings of electronic states produced by the electron-phonon interaction in semiconductors and of their dependence on temperature.
Abstract: We present calculations of the lifetime broadenings of electronic states produced by the electron-phonon interaction in semiconductors and of their dependence on temperature. This effect is evaluated as a complex self-energy of the electronic states. The real part of this self-energy describes a shift of the bands with temperature, whereas the imaginary part is responsible for the broadening of the states. For the calculations based on perturbation theory to second order in atomic displacement we use a local pseudopotential with a basis of 59 plane waves, the lattice dynamics of Weber's bond-charge model, and a tetrahedron method for doubly constrained Brillouin-zone integrals. Results are given for points along the \ensuremath{\Lambda} and \ensuremath{\Delta} direction of the Brillouin zone for Si and Ge, thus obtaining the temperature dependence of the broadening parameters of the interband critical points ${E}_{0}$, ${E}_{0}^{\mathcal{'}}$, ${E}_{1}$, and ${E}_{2}$. The results are compared with experimental data obtained from ellipsometric measurements of the temperature dependence of the dielectric function. Remarkable agreement between calculated and measured data is found.
87 citations
TL;DR: In this article, a novel homodyne detection technique which avoids optoelectronic phase locking by using stimulated Brillouin gain to selectively amplify the signal carrier is described, which avoids optical phase locking.
Abstract: A novel homodyne detection technique which avoids optoelectronic phase-locking by using stimulated Brillouin gain to selectively amplify the signal carrier is described.
85 citations
TL;DR: In this article, the pseudopotential method within the local density approximation was used to investigate the static and structural properties of NaCl and KCl and calculated the electronic energy levels at symmetry points in the Brillouin zone as a function of volume.
Abstract: The pseudopotential method within the local-density approximation is used to investigate the static and structural properties of NaCl and KCl. Calculated values for the lattice constants and bulk moduli are in good agreement with experiment. The pressure phase transformation to the CsCl structure is studied, and the role of the C44 shear instability as a possible transformation path is investigated and dismissed. The tetragonal distortion of the CsCl phase, which has been found in other alkali halides at high pressures, appears not to exist in KCl. Finally the authors have calculated the electronic energy levels at symmetry points in the Brillouin zone as a function of volume.
85 citations
TL;DR: For coverages up to one monolayer, Cu adsorbs in a pseudomorphic structure on the Ru(0001) surface with a 5% tensile strain to be the antibonding partner of a pair of Cu(3d)-Ru*4d)--derived interface states.
Abstract: For coverages up to one monolayer, Cu adsorbs in a pseudomorphic structure on the Ru(0001) surface with a 5% tensile strain. Angle-resolved photoemission near the K point in the surface Brillouin zone reveals a state -1.5 eV below the Fermi level which appears localized in the Cu and outermost Ru layers. This state is confirmed by surface linearized, augmented plane-wave calculations to be the antibonding partner of a pair of Cu(3d)-Ru*4d)--derived interface states.
84 citations
TL;DR: This work presents a theoretical study of the bulk and surface magnons of a semi-infinite stack of two different ferromagnetic films, modeled by a simple-cubic lattice of spins coupled via nearest-neighbor exchange (Heisenberg ferromagnet).
Abstract: We present a theoretical study of the bulk and surface magnons of a semi-infinite stack of two different ferromagnetic films. Each film is modeled by a simple-cubic lattice of spins coupled via nearest-neighbor exchange (Heisenberg ferromagnet). The superlattice has a larger periodicity in the direction perpendicular to the slabs and therefore many magnon branches in the folded Brillouin zone. In the gaps exisiting between these magnon branches appear the surface-localized magnons. The simplicity of our model allows one to obtain in closed form the bulk and (001) surface Green's functions for this magnetic superlattice. The analytic knowledge of these functions enables us to study easily all the bulk and and surface magnetic properties of a ferromagnetic superlattice. We give here the analytic expression we obtained for the folded bulk magnons and also the expression that gives the surface-localized modes, which may appear within the extra gaps which exist between the folded bulk bands. One figure for a specific case illustrates these results.
TL;DR: In this paper, the Brillouin Stokes shift was measured to be 150 MHz in contrast to previous measurements of ∼20 MHz, and a narrow linewidth external cavity semiconductor laser was used as the pump source and a gain of 4.3 dB/mW pump power was measured.
Abstract: The propagation loss is canceled, and 5 dB of net gain is obtained by Brillouin amplification in a 37.5‐km‐long single‐mode optical fiber. A narrow linewidth external cavity semiconductor laser is used as the pump source and a gain of 4.3 dB/mW pump power is measured. The Brillouin linewidth is measured to be 150 MHz in contrast to previous measurements of ∼20 MHz. The Brillouin Stokes shift was 11.3 GHz at 1.5 μm wavelength.
TL;DR: In this article, the one-electron Schrodinger equation for a noncollinear magnet with arbitrary direction of atomic spin in the magnetic unit cell (MUC) is presented.
Abstract: The one-electron Schrodinger equation for a noncollinear magnet (NCM) with arbitrary direction of atomic spin in the magnetic unit cell (MUC) is presented. By analogy with the usual KKR method the secular equation for an NCM is deduced. The symmetry of the problem is discussed on the basis of spin space groups. It is shown that the symmetry consideration often leads to the secular equation factorising anywhere in the Brillouin zone. The calculation of the electron spectrum of the spin spiral for BCC Fe has been carried out and the calculated energy of the spin wave is in good agreement with the experimental value.
TL;DR: In this article, a method of data analysis is presented delivering simultaneously the complete set of elastic stiffness constants and the determination of the principal refractive indices by Brillouin spectroscopy.
Abstract: General aspects of high performance Brillouin spectroscopy in polymers using special scattering geometries such as 90A-scattenng geometry are discussed. Technical improvements are reported resulting in absolute accuracies up to 0.05 % for sound velocity determination. A method of data analysis is presented delivering simultaneously the complete set of elastic stiffness constants. The influence of birefringence on the Brillouin line shifts in anisotropic polymeric systems is estimated and techniques to reduce this influence are proposed. The determination of the principal refractive indices by Brillouin spectroscopy is discussed. Furthermore, a quantityD
X
, which is sensitive to hypersonic relaxation processes, is introduced.
TL;DR: In this article, a study of empty electronic bulk and surface states on the three low indexed copper surfaces employing momentum resolved inverse photoemission was performed, and the bulk electronic features may be well understood in the frame work of the bulk direct transition model using state of the art band structure calculations.
Abstract: We have performed a study of empty electronic bulk and surface states on the three low indexed copper surfaces employing momentum resolved inverse photoemission. The bulk electronic features may be well understood in the frame work of the bulk direct transition model using state of the art band structure calculations. Surface states of both, the crystal derived and the image potential induced type have been identified and were found to agree with previous work. Several radiative transitions into unoccupied bands were also investigated at elevated temperatures. Characteristic temperatures of an exponential attenuation law are distinctly different between surface and bulk transitions. However, no systematic behaviour of bulk transitions at different points of the Brillouin zone could be established.
TL;DR: In this paper, the initial stages of interface formation between CaF2 and Si(111) have been studied with both core-level and angle-resolved valence band photoemission spectroscopy.
Abstract: The initial stages of interface formation between CaF2 and Si(111) have been studied with both core‐level and angle‐resolved valence band photoemission spectroscopy. Both the Si 2p and Ca 3p core levels indicate that a Si–Ca bond is present at the CaF2–Si(111) interface. Annealing of thin CaF2 films at 700–800 °C results in preferential evaporation of F, and the surface undergoes a number of reconstructions until a stable Si(111):Ca 3×1 reconstruction is obtained on which there is calcium, but no fluorine. This surface exhibits a surface state with an upward dispersion of 0.4 eV towards the K point of the 1×1 surface Brillouin zone. Our results show that the CaF2 molecule can be dissociated on the Si(111) surface at typical epitaxial growth temperatures, with the Ca being more strongly adsorbed to the Si than is the F.
TL;DR: The dispersion curve of the Rayleigh phonon on Cu(100) has been measured by high resolution electron energy loss spectroscopy throughout the two-dimensional Brillouin zone in the ΓX direction.
IBM1
TL;DR: The current-voltage characteristics of As-GaAs are interpreted as resonant tunneling through confined states in Ga, at the X point of the Brillouin zone.
Abstract: The current-voltage characteristics of ${\mathrm{Ga}}_{1\mathrm{\ensuremath{-}}\mathrm{x}}$${\mathrm{Al}}_{\mathrm{x}}$As-GaAs-${\mathrm{Ga}}_{1\mathrm{\ensuremath{-}}\mathrm{x}}$${\mathrm{Al}}_{\mathrm{x}}$ As double-barrier devices show, in addition to resonant tunneling via quasibound \ensuremath{\Gamma} states, well-defined structures corresponding to energies higher than the barrier height. These new features are interpreted as resonant tunneling through confined states in ${\mathrm{Ga}}_{1\mathrm{\ensuremath{-}}\mathrm{x}}$${\mathrm{Al}}_{\mathrm{x}}$As, at the X point of the Brillouin zone.
TL;DR: In this paper, the dispersion of the Rayleigh wave on Cu(100) has been measured by high resolution electron energy loss spectroscopy (EELS) throughout the two-dimensional Brillouin zone in the\(\overline {\Gamma M} {\text{ - direction}}\).
Abstract: The dispersion of the Rayleigh wave on Cu(100) has been measured by high resolution electron energy loss spectroscopy (EELS) throughout the two-dimensional Brillouin zone in the\(\overline {\Gamma M} {\text{ - direction}}\). The experimental data can be matched with a nearest neighbour central force model when the force constant between the first and second layerk12 is stiffened by 20%. However, the data are likewise explained by assuming stress within the surface layer. The stress could arise from a tendency of the surface layer to contract.
TL;DR: It is demonstrated that both the empirical pseudopotential method (EPM) and the linear combination of atomiclike orbitals (LCAO) approach are capable of producing consistent electronic charge distributions in a compound semiconductor.
Abstract: We demonstrate that both the empirical pseudopotential method (EPM) and the linear combination of atomiclike orbitals (LCAO) approach are capable of producing consistent electronic charge distributions in a compound semiconductor. Since the EPM approach is known to produce total valence electron charge densities which compare well with experimental x-ray data (e.g., Si), this work serves as a further test for the LCAO method. In particular, the EPM scheme, which uses an extended plane-wave basis, and the LCAO scheme, which employs a localized Gaussian basis, are used, with the same empirical potential as input, to analyze both the total valence electron charge density and the charge density of the first conduction band at the \ensuremath{\Gamma}, L, and X k points of the Brillouin zone. These charge densities are decomposed into their s-, p-, and d-orbital contributions, and this information is used to interpret the differences in the topologies of the conduction bands at \ensuremath{\Gamma}, L, and X. Such differences are crucial for a comprehensive understanding of interstitial impurities and the response of specific band states to perturbations in compound semiconductors.
TL;DR: In this paper, a novel technique for controlling the bandwidth of a fiber Brillouin amplifier is proposed and demonstrated using a frequency-modulated pump laser, in this case an external-cavity semiconductor laser.
Abstract: A novel technique for controlling the bandwidth of a fibre Brillouin amplifier is proposed and demonstrated. By using a frequency-modulated pump laser, in this case an external-cavity semiconductor laser, we have increased the bandwidth of useful gain by more than one order of magnitude. The scheme can be used to tailor the gain characteristics of fibre Brillouin amplifiers to
TL;DR: In this article, the authors developed a model to investigate the interaction of a subpicosecond laser pulse with a direct-gap semiconductor, where carrier distributions are extremely far from equilibrium and nonequilibrium LO phonons are generated at the center of the Brillouin zone.
TL;DR: In this article, the authors derived an approximate Hamiltonian which describes a conduction band and a virtual boound states band coupled by a Kondolike interaction, and the ground state of this Hamiltonian can be magnetic or not or superconducting depending on the filling of the virtual bound states band.
TL;DR: The structural stability of the rhombohedral and simple cubic phases is studied for the group-VA elements and the calculated phonon frequencies for the longitudinal acoustic mode at the corner of the simple-cubic Brillouin zone are found to soften, suggesting that all group-V elements are likely to form in therhombohedral structure with respect to the simple cubic phase.
Abstract: The structural stability of the rhombohedral and simple cubic phases is studied for the group-VA elements. Using an ab initio pseudopotential total-energy method, the calculated phonon frequencies for the longitudinal acoustic mode at the corner of the simple-cubic Brillouin zone are found to soften. This suggests that all group-V elements are likely to form in the rhombohedral structure with respect to the simple cubic phase. At high pressures, the rhombohedral stability is diminished, causing a transition to the simple-cubic structure.
TL;DR: The optical properties of GaAs-Al sub x Ga sub 1-xAs superlattices are calculated as a function of the frequency andsuperlattice structure and results are in good agreement with the experimental data.
Abstract: The optical properties of GaAs-Al sub x Ga sub 1-xAs superlattices are calculated as a function of the frequency and superlattice structure. The comutations are performed using a partition method which combines the vectors k.p method with the pseudopotential technique. The influence of the super-structure on the electronic properties of the systems is accounted for by appropriate quantization conditions. The anisotropy and structure dependence of the dielectric constant result mainly from the contribution of the gamma region while the contributions of the other regions of the Brillouin zone are rather insensitive to the superlattice structure. The superlattice index of refraction values are shown to attain maxima at the various quantized transition energies, where for certain structures, the difference between the refractive indices of the superlattices and its corresponding Al sub x Ga sub 1-xAs alloy can be as large as 2%. In general results are in good agreement with the experimental data.
TL;DR: In this paper, the authors investigated the effect of the spin split off-heavy hole band transition on the temperature sensitivity of the longer-wavelength semiconductor lasers used for optical fiber communications.
Abstract: Intervalence band absorption (IVBA) has been proposed as a possible cause of the temperature sensitivity of threshold currents in the longer-wavelength semiconductor lasers used for optical fibre communications. In view of the potential importance of this effect, IVBA coefficients for the spin split off-heavy hole band transition have been evaluated for GaAs, Ga0.47In0.53As and Ga0.28In0.72As0.6P0.4 for temperatures in the range 150
TL;DR: Inelastic neutron spectra of B quartz were recorded at various temperatures, using triple axis neutron spectrometry as discussed by the authors, and they confirmed the existence of a very low-lying phonon branch along the 1,0,0⟩ directions, which exhibits a marked temperature dependence, in particular near the Brillouin zone center.
Abstract: Inelastic neutron spectra of B quartz were recorded at various temperatures, using triple axis neutron spectrometry. Our observations confirm the existence of a very low-lying phonon branch along the ⟨1,0,0⟩ directions, which exhibits a marked temperature dependence, in particular near the Brillouin zone center. This branch is very anisotropic in the (0,0,1) plane. Within the B phase a maximum of quasi elastic scattering is observed for q ≃ 0.03a*, premonitory to the appearance of satellite reflexions in the modulated phase. In addition, a transverse acoustic mode exhibits an anisotropic behaviour which is attributed to a coupling with the soft-mode. The results are consistent with a phenomenological model of the incommensurate phase transition and with a lattice dynamical model involving rigid SiO4 tetrahedra motions.
TL;DR: In this article, the surface states are derived from dangling bond electrons on silicon surface atoms that are modified by the presence of the group III atoms, and two low-energy configurations for the groups III ad-atoms give similar theoretical surface band structures.
TL;DR: The accuracy of the phase-conjugate signal produced by stimulated Brillouin scattering in a waveguide is theoretically investigated in this paper, and it is shown that this output dominates the non-phase-matching signal from stimulated BLE.
Abstract: The accuracy of the phase-conjugate signal produced by stimulated Brillouin scattering in a waveguide is theoretically investigated. Contradictions between earlier phase-conjugation theories are resolved and are shown to be due solely to differing treatments of the non-phase-matched Brillouin output. We find that this output dominates the nonconjugate signal from stimulated Brillouin scattering.
TL;DR: A generalisation of the analytical tetrahedron method is given in this paper, which allows the evaluation of spectral functions over the entire complex energy plane and leads to compact and transparent formulae which are free of singularities and well suited for automatic computation.
Abstract: A generalisation of the analytical tetrahedron method is given which allows the evaluation of spectral functions over the entire complex energy plane. Linear interpolation of both the matrix element and the dispersion relations leads to compact and transparent formulae which are free of singularities and well suited for automatic computation. An illustrative calculation is presented of the lattice Green function G(E) for the simple cubic lattice for Im E=0.001 and 0.1.