Showing papers on "Brillouin zone published in 1995"
TL;DR: In this article, a distributed strain and temperature sensing technique that uses Brillouin scattering in single-mode optical fibers is presented, which is based on strain- and temperature-induced changes in the frequency shift.
Abstract: This paper reviews the developments of a distributed strain and temperature sensing technique that uses Brillouin scattering in single-mode optical fibers. This technique is based on strain- and temperature-induced changes in the Brillouin frequency shift. Several approaches for measuring the weak Brillouin line are compared. >
685 citations
TL;DR: In this article, the ensemble Monte Carlo technique is used to calculate the basic electronic transport properties for both zincblende and wurtzite crystal phases of bulk gallium nitride.
Abstract: The ensemble Monte Carlo technique including the details of the first four conduction bands within the full Brillouin zone is used to calculate the basic electronic transport properties for both zincblende and wurtzite crystal phases of bulk gallium nitride. The band structure throughout the Brillouin zone is determined using the empirical pseudopotential method. Calculations of the electron steady‐state drift velocity, average energy, valley occupancy and band occupancy in the range of electric fields up to 500 kV/cm are presented. It is found that the threshold electric field for intervalley transfer is greater and that the second conduction band is more readily occupied in wurtzite than in zincblende GaN over the range of electric fields examined here.
312 citations
01 Jan 1995
TL;DR: Lattice dynamics is closely related to the thermodynamics of solids and elasticity theory which have both been studied much before that date as discussed by the authors, and is often referred to as lattice dynamics.
Abstract: The atoms in a solid will at any temperature oscillate around their equilibrium configuration, at zero temperature due to their zero point motion. This motion of the atoms is the major heat bath in solids and is responsible for important properties such as heat capacity, thermal conductivity, lattice expansion, displacive phase transitions etc. The theory of these lattice vibrations is often referred to as lattice dynamics. In its present form it is now eighty years old, originating in papers by Born and von Karman in 1912. Lattice dynamics is closely related to the thermodynamics of solids and elasticity theory which have both been studied much before that date.
203 citations
TL;DR: A zone-selection effect, wherein interference between photoelectron amplitudes from the two atoms in each graphene unit cell cause both $\sigma and \ensuremath{\sigma} states to appear with different intensity in otherwise equivalent Brillouin zones, is observed.
Abstract: Experimental and theoretical graphite valence-band photoelectron angular distributions are presented and compared. We observe a zone-selection effect, wherein interference between photoelectron amplitudes from the two atoms in each graphene unit cell cause both \ensuremath{\sigma} and \ensuremath{\pi} states to appear with different intensity in otherwise equivalent Brillouin zones. To simulate the experimental graphite valence-band photoelectron angular distributions, our simple model includes effects of (1) valence-band wave functions and (2) the relative emission path-length difference, from the atoms in each unit cell to one's detector (which is determined by the experimental geometry).
194 citations
TL;DR: In this article, the authors measured thermally induced energy shifts of the Shockley surface states observed around the center \ gG of the surface Brillouin zones on the noble metal (111) surfaces.
192 citations
TL;DR: A systematic study of the electronic structure of Al-based Hume-Rothery alloys containing transition elements performed with the use of the linear muffin-tin orbital in atomic-sphere approximation method, observing a strong deviation from the two classical limits.
Abstract: We present a systematic study of the electronic structure of Al-based Hume-Rothery alloys containing transition elements performed with the use of the linear muffin-tin orbital in atomic-sphere approximation method. Our analysis focuses on the formation of the pseudogap at the Fermi level leading to the stability of materials containing transition-metal elements in small concentration. From the self-consistent calculated density of states, we observe a strong deviation from the two classical limits: (a) the Friedel-Anderson virtual bond state's model and (b) the nearly-free-electron diffraction by some Bragg planes in the usual Hume-Rothery picture of simple metal alloys. Transition-metal atoms have a crucial role on electronic structure via the combined effect of the sp-d hybridization and of a strong interaction between the Fermi surface and a predominant Brillouin zone.
142 citations
TL;DR: A complete mapping in the Brillouin zone of the structural instability associated with the ferroelectric phase transitions of KNbO$_3$ has been obtained by first-principles calculations using an LAPW linear response approach.
Abstract: A complete mapping in the Brillouin zone of the structural instability associated with the ferroelectric phase transitions of ${\mathrm{KNbO}}_{3}$ has been obtained by first-principles calculations using a linear response approach. The wave-vector dependence of the instability reveals pronounced two-dimensional character, which corresponds to chains oriented along $〈100〉$ directions of displaced Nb atoms. The results are discussed in relation to models of the ferroelectric phase transitions.
116 citations
TL;DR: The defects considered here are already negligible for reasonably small unit cells, but adequate sampling of the Brillouin zone is found to be essential for these metallic systems, even for systems containing more than 100 atoms per unit cell.
Abstract: The vacancy formation energies and (Mg, Al, and Si) impurity heats of solution are calculated for Al and Mg using a first-principles pseudopotential approach and large supercells. While the interaction of the defects considered here are already negligible for reasonably small unit cells, adequate sampling of the Brillouin zone is found to be essential for these metallic systems, even for systems containing more than 100 atoms per unit cell; e.g., the vacancy formation energy of Al for 108 atoms per cell has the incorrect sign if only the \ensuremath{\Gamma} point is sampled. When the volume and structural relaxations are treated consistently, heats of formation and solution and relaxation volumes are obtained that are in good agreement with the available experimental data. Simple trends in the relaxations around the impurities in the various materials can be understood in terms of the size of the impurities compared with the host atoms. Contrary to some commonly used models, the energetics of the impurities are found to be dominated by electronic, rather than elastic, contributions. The defect-induced changes to the local electronic structure are also discussed.
93 citations
TL;DR: In this article, a scanning interference pattern produced by intersecting two cw lasers generates the density variation (acoustic phonons) through the thermal expansion for a light absorbing liquid.
Abstract: We have developed a new method of phonon spectroscopy using forced Brillouin scattering: A scanning interference pattern produced by intersecting two cw lasers generates the density variation (acoustic phonons) through the thermal expansion for a light-absorbing liquid. When the dispersion relation of phonons is satisfied, phonons are generated resonantly in the liquid. Continuous tuning of the frequency difference between the two lasers enables us to measure a resonance spectrum of light-excited phonons using light scattering phenomena. We demonstrate that this resonance spectrum is equivalent to the Brillouin spectrum of thermal phonons both experimentally and theoretically.
93 citations
TL;DR: The structural, electronic, and dynamical properties of the Si(100) surface within the density-functional theory were investigated in this article, based on the plane-wave pseudopotential method combined with the slab supercell description for the surface.
87 citations
TL;DR: In this article, the azimuthal anisotropy in the normal incidence reflectivity of a clean and adsorbate-covered single-crystal metal surface was measured.
Abstract: We report spectroscopic measurements of the azimuthal anisotropy in the normal incidence reflectivity of a clean and adsorbate-covered single-crystal metal surface: Reflectance anisotropy spectra were taken between 1.5 and 6 eV from Cu(110). On the clean surface, a sharp resonance is found which is assigned to a transition between two surface states at the $\overline{Y}$ point of the surface Brillouin zone. The resonance can be removed by adsorption, and its energetic position is in good agreement with photoemission and inverse photoemission work.
TL;DR: A first-principles pseudopotential study of 11 phases of silicon finds good agreement with experiments and with some previous calculations but a few discrepancies remain and some insights are gained into the high-pressure phase diagram of silicon.
Abstract: A first-principles pseudopotential study of 11 phases of silicon is reported: diamond (cd), body-centered cubic (bcc), face-centered cubic (fcc), body-centered tetragonal (bct), simple hexagonal (sh), hexagonal-close-packed (hcp), double-hexagonal-close-packed (dhcp), simple cubic (sc), \ensuremath{\beta}-tin, a body-centered cubic structure with eight atoms per unit cell (bc8), and a simple tetragonal structure with 12 atoms per unit cell (st12) For each structure and for each volume considered we have minimized the energy with respect to all structural degrees of freedom We have used large basis sets and very careful integrations over the Brillouin zone to resolve the small energy differences between structures, and our pseudopotentials incorporate nonlinear core exchange-correlation corrections, leading to more accurate results than those of previous calculations We find good agreement with experiments and with some previous calculations but a few discrepancies remain and we gain some insights into the high-pressure phase diagram of silicon
TL;DR: In this paper, the Brillouin light scattering technique was successfully applied for determining the five effective elastic constants of a single transparent film of hexagonal symmetry, in the micron range of thicknesses.
Abstract: In this work it is shown that the Brillouin light scattering technique can be successfully applied for determining the five effective elastic constants of a single transparent film of hexagonal symmetry, in the micron range of thicknesses. Measurements have been performed on a polycrystalline ZnO film, about 1.3 mu m thick, supported by a Si substrate. A major result of this work is that the elastic constant c66 is selectively determined for the first time from detection of the shear horizontal mode travelling parallel to the film surface. Similarly, a selective determination of c11 is attained from observation of the longitudinal mode guided by the film. The three remaining elastic constants, namely c13, c33, and c44, can be then obtained from detection of the Rayleigh surface mode and of the longitudinal bulk wave propagating at different angles from the surface normal.
01 Jan 1995
TL;DR: Brillouin light scattering is generally referred to as the inelastic scattering of an incident optical wave field by thermally excited elastic waves (elastic waves of thermal origin are usually called acoustic phonons) in a sample as mentioned in this paper.
Abstract: Brillouin light scattering is generally referred to as the inelastic scattering of an incident optical wave field by thermally excited elastic waves (elastic waves of thermal origin are usually called acoustic phonons) in a sample. This subject was first investigated early in the century by Brillouin(1) and Mandelshtam(2) in the case of scattering from transparent materials. Since the advent of the laser as a powerful source of monochromatic light, Brillouin scattering has received considerable interest for characterizing elastic and optoelastic bulk properties of materials.3,4 More recently with the introduction of high-contrast spectrometers,(5) scattering from opaque materials can be studied, thereby permitting considerable advances in the study of surface acoustic waves in solids. In the last decade, Brillouin scattering from surfaces, more often called surface Brillouin scattering (SBS), has been widely used to investigate elastic properties of thin films, interfaces, and layered materials.
TL;DR: The effective charge for multimagnon infrared absorption assisted by phonons in a perovskitelike antiferromagnet and the spectra for two-magnon absorption using interacting spin-wave theory are calculated.
Abstract: We calculate the effective charge for multimagnon infrared absorption assisted by phonons in a perovskitelike antiferromagnet and we compute the spectra for two-magnon absorption using interacting spin-wave theory. The full set of equations for the interacting two-magnon problem is presented in the random-phase approximation for arbitrary total momentum of the magnon pair. The spin-wave theory results fit very well the primary peak of recent measured bands in the parent insulating compounds of cuprate superconductors. The line shape is explained as being due to the absorption of one phonon plus a new quasiparticle excitation of the Heisenberg Hamiltonian that consists of a long-lived virtual bound state of two magnons (bimagnon). The bimagnon states have well-defined energy and momentum in a substantial portion of the Brillouin zone. The higher-energy bands are explained as one phonon plus higher multimagnon absorption processes. Other possible experiments for observing bimagnons are proposed. In addition we predict the line shape for the spin-1 system ${\mathrm{La}}_{2}$${\mathrm{NiO}}_{4}$.
TL;DR: A nearest-neighbor effective Hamiltonian is derived, which takes account of the mixing of higher Co + ion crystal-field levels in a self-consistent manner and is found to be in quantitative agreement with experiment.
Abstract: The lowest-lying excited states in the S= 2 one-dimensional Ising-like antiferromagnet CsCoC13 consist of domain-wall (soliton) pair states. Although the dynamical response function S(g, to) has been calculated for these states, it has not proved possible to explain the results of neutron scattering and Raman experiments without recourse to the introduction of extra terms in the spin Hamiltonian. We argue against the two modifications to the Hamiltonian of CsCoC13 proposed in previous papers, a staggered field term arising from a mean field approach to exchange mixing, and next-nearest-neighbor intrachain coupling, as being unphysical. Instead we derive a nearest-neighbor effective Hamiltonian, which takes account of the mixing of higher Co + ion crystal-field levels in a self-consistent manner. We also present a high-resolution inelastic neutron scattering experiment on CsCoC13, which has allowed the dispersion of the excited states across the Brillouin zone to be studied more carefully than before. These results give a direct measure of S(g, to) in the onedimensional phase where there is a continuum of excited states, and in the three-dimensionally ordered phases, where weak interchain interactions split the continuum into a "Zeeman ladder" of discrete states. The predictions of our theory are found to be in quantitative agreement with experiment.
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TL;DR: The bi-layer Hubbard model with realistic LDA derived hopping integrals is studied, which combines this realistic tight-binding (TB) model with many-body effects accounts for anomalous properties of cuprate superconductors.
Abstract: We analyze the generic features of the energy spectrum for two coupled CuO$_2$ layers with a realistic extended Hubbard model. The quasiparticle bands exhibit flat regions near X(Y) points in the Brillouin zone with a large reduction of the bonding-antibonding splitting, and pinning of extended van-Hove singularity to the Fermi level, which is more efficient for a bi-layers than for a single layer. In contrast to the results with simpler models, the superconducting temperature for d$_{x^2-y^2}$ pairing is not lowered by the bi-layer hopping.
TL;DR: This work has measured the temperature dependence of the peak position and linewidth of the 42.5 meV phonon branch in a twinned single crystal of YBa 2Cu 3O 7 as a function of wave vector q and observed an order of magnitude smaller softening and no linewsidth broadening.
Abstract: We have measured the temperature dependence of the peak position and linewidth of the 42.5 meV phonon branch in a twinned single crystal of YBa 2Cu 3O 7 as a function of wave vector q. In the s100dys010d direction in the Brillouin zone, considerable softening and broadening occur below the superconducting transition temperature Tc at some values of q. We observe an order of magnitude smaller softening and no linewidth broadening for q in the s110dy ° 110 ¢ direction. Possible implications of these findings for the symmetry of the superconducting order parameter are discussed.
TL;DR: In this paper, a model of the low-frequency Raman scattering intensity in glasses is proposed, which describes the spectrum in the region of the boson peak, typical of glasses.
Abstract: A model of the low‐frequency Raman scattering intensity in glasses is proposed, which describes the spectrum in the region of the boson peak, typical of glasses. The model considers the boson peak as a result of first‐order light scattering by harmonic quasilocalized vibrations. The amplitude, frequency, and polarization dependence of the light on the vibrational coupling coefficient C(ω) are estimated. The model predicts a linear frequency dependence of C(ω) in the region of the boson peak and the depolarization ratio as a function of the relative contribution of the longitudinal and transverse‐type motions which comprise these quasilocal vibrational modes. Low‐frequency Raman and Brillouin measurements have been made on SiO2 glass in order to check the predictions of the model regarding the amplitude and integrated intensity of the boson peak. The estimated ratio of these values to those of the Brillouin lines are in good agreement with experiment. Comparison of the theoretical and experimental values o...
TL;DR: In this paper, the frequency dependence of real and imaginary parts of the complex dielectric constant ϵ(ω) in compounds XMnY (X = Ni, Pd, Pt, Cu; Y = Sb, Sn) having Clb structure are investigated in the spectral range ħω = 0.05 to 8 eV.
Abstract: The frequency dependence of the real and imaginary parts of the complex dielectric constant ϵ(ω) in compounds XMnY (X = Ni, Pd, Pt, Cu; Y = Sb, Sn) having Clb structure are investigated in the spectral range ħω = 0.05 to 8 eV. The values of conduction electron plasma and relaxation frequencies ωp and γ, respectively, are determined. The evolution of interband conduction and electron energy-loss function -Im (e−1) for varying compositions is studied. In all the compounds, apart from the main absorption band located in the spectral range 1 to 7 eV, a low-energy (ħω = 0.3 to 0.7 eV) interband absorption is revealed. An estimation is made of the energy gap at point Γ of the Brillouin zone in the minority-spin subbands () for NiMnSb using optical data.
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10 Feb 1995TL;DR: In this article, the authors used an intensity modulator in the optical loop of a Brillouin fiber optic gyroscope to attenuate the counterpropagation of the counter-propagating light wave.
Abstract: A Brillouin fiber optic gyroscope includes an intensity modulator in the optical loop which periodically attenuates the Brillouin light waves counterpropagating in the optical loop so that the counterpropagating Brillouin waves each propagate as square waves. The use of square wave modulation for the counterpropagating light wave reduces the cross-effect of the Brillouin waves to substantially the same magnitude as the self-effect so that the non-reciprocal Kerr effect is substantially reduced or eliminated. In order to support the counterpropagating square waves, the optical loop is pumped with pump light having frequency components selected to pump the optical fiber to provide Brillouin light at frequencies necessary to generate square waves in the counterpropagating Brillouin light waves. In addition, the Brillouin light must be generated at the correct intensity and phase relationship to form the square wave. Because the relationship between the pump light and the generated Brillouin light is a non-linear function, the relative magnitudes of the frequency components of the pump light are selected to be different from the relative magnitudes of the Brillouin light so that when the pump light is applied to the optical loop, the transfer function results in the correct magnitudes for the frequency components of the Brillouin light. The intensity modulator assures that the Brillouin light is maintained in the proper phase relationship to maintain a square waveform.
TL;DR: In this paper, the formation of electrostrictive gratings in fluids is calculated by inclusion of viscosity and heat transfer, and the reflectivity of the grating performs a damped oscillation with alternately higher and lower maxima.
Abstract: The formation of electrostrictive gratings in fluids is calculated by inclusion of viscosity and heat transfer. The reflectivity of the grating performs a damped oscillation with alternately higher and lower maxima. The normalized difference in height is determined by the thermal conductivity of the medium. Measurements have been performed for argon and nitrogen and are compared with the theory. Furthermore, the combined effect of electrostriction and radiative absorption is discussed.
TL;DR: The conjecture that stress-induced amorphization arises from themore near simultaneous accessibility of multiple modes of instability in the highly metastable parent crystalline phase is supported.
Abstract: ${\mathrm{CaSiO}}_{3}$ and ${\mathrm{MgSiO}}_{3}$ perovskites are known to undergo solid-state crystal to amorphous transitions near ambient pressure when decompressed from their high-pressure stability fields In order to elucidate the mechanistic aspects of this transition we have performed detailed molecular-dynamics simulations and lattice-dynamical calculations on model silicate perovskite systems using empirical rigid-ion pair potentials In the simulations at low temperatures, the model perovskite systems transform under tension to a low-density glass composed of corner shared chains of tetrahedral silicon The amorphization is initiated by a thermally activated step involving a soft polar optic mode in the perovskite phase at the Brillouin zone center Progression of the system along this reaction coordinate triggers, in succession, multiple barrierless modes of instability ultimately producing a catastrophic decohesion of the lattice An important intermediary along the reaction path is a crystalline phase where silicon is in a five-coordinate site and the alkaline-earth metal atom is in eightfold coordination At the onset pressure, this transitory phase is itself dynamically unstable to a number of additional vibrational modes, the most relevant being those which result in transformation to a variety of tetrahedral chain silicate motifs These results support the conjecture that stress-induced amorphization arises from the near simultaneous accessibility of multiple modes of instability in the highly metastable parent crystalline phase
TL;DR: Using a recently developed method for calculating series expansions of the excitation spectra of quantum lattice models, the spin-wave spectra for square lattice, S=1/2 Heisenberg-Ising antiferromagnets are obtained.
Abstract: Using a recently developed method for calculating series expansions of the excitation spectra of quantum lattice models, we obtain the spin-wave spectra for square lattice, S=1/2 Heisenberg-Ising antiferromagnets. The calculated spin-wave spectrum for the Heisenberg model is close to but noticeably different from a uniformly renormalized classical (large-S) spectrum with the renormalization for the spin-wave velocity of approximately 1.18. The relative weights of the single-magnon and multiple-magnon contributions to neutron-scattering spectra are obtained for wave vectors throughout the Brillouin zone.
TL;DR: In this paper, surface phonon dispersion curves have been measured for clean and hydrogen covered Rh(111) surfaces along the high symmetry directions of the surface Brillouin zone using high-resolution He-atom scattering.
TL;DR: In this paper, a simple model defines an effective steady SBS gain, and may explain the dispersion of available measured values, as well as a reduction of the overall SBS gains.
Abstract: Transverse material inhomogeneities yielding the guiding properties of any optical fibre also cause a variation of stimulated Brillouin resonance frequency, and thus a spectral broadening as well as a reduction of the overall SBS gain. A simple model defines an effective steady SBS gain, and may explain the dispersion of available measured values.
TL;DR: In this paper, multiband coupling effects on electronic intersubband single particle excitations (SPE) of IR and Raman processes in type I quantum wells (QWs) were discussed.
Abstract: We discuss multiband coupling effects on electronic intersubband single particle excitations (SPE) of infrared (IR) and Raman processes in type I quantum wells (QWs). Interband couplings between Γc1‐Γv15, Γc1‐Γc15, and Γc15‐Γv15 bulk band edges are treated within 14‐band k⋅p first‐order perturbation theory. Enhanced band‐mixing effects are observed at Brillouin zone center (k∥=0) because of quantization effects (kz≠0). For zinc‐blende‐type QWs, Γc15‐Γv15 band‐mixing effects at high‐lying Γc1 conduction subbands contribute (x,y)‐polarized IR and z(x,x)z‐ and z(x,y)z‐polarized Raman intersubband SPE. Intersubband polarization splittings occur when the QWs are under biaxial strains.
TL;DR: In this article, theoretical and experimental results on three main effects determining the frequency stability of a Brillouin fiber ring laser, namely, the temperature effects and the nonlinear Kerr and frequency pulling effects are presented.
Abstract: This study shows theoretical and experimental results on three main effects determining the frequency stability of a Brillouin fiber ring laser, namely: the temperature effects and the nonlinear Kerr and frequency pulling effects. The oscillation frequency in a Brillouin fiber ring laser is determined mainly by the axial mode of the cold resonator located under the Brillouin gain curve that experiences the highest gain. This oscillation frequency is therefore temperature dependent since both the free spectral range (FSR) and the gain curve center depend on the temperature. The FSR variation gives rise to a continuous lasing frequency variation while the gain curve shift leads to mode hopping. In addition to these temperature effects, the nonlinear Kerr effect and the mode pulling effect will also slightly shift the lasing frequency away from the resonant frequency of the cold resonator. The Kerr effect depends only on the pump power, while the mode pulling effect depends on both the pump power and the relative location between the lasing mode and the gain curve center. The results of this study are useful in many BFRL applications such as Brillouin fiber-optic gyroscopes, microwave generators and frequency shifters. >
TL;DR: In this paper, the longitudinal and transverse Brillouin spectra along phonon direction have been measured as a function of temperature (50-475 K) in singlecrystal PbMg1/3Nb2/3O3 with scattering angles θs=180° and 32.5±0.2°.
Abstract: The longitudinal (LA) and transverse (TA) Brillouin spectra along [001] phonon direction have been measured as a function of temperature (50–475 K) in single‐crystal PbMg1/3Nb2/3O3 with scattering angles θs=180° and 32.5±0.2°. The Brillouin frequency shift with decreasing temperature shows a broad softening anomaly for both LA and TA phonon modes. For θs=180°, a gradual growth in damping with maximum near 270 K is observed and is attributed to order parameter fluctuations. An additional Landau–Khalatnikov maximum is also observed at Tc∼212 K. This anomaly implies a rapid growth of ferroelectric ordering near Tc and is consistent with the earlier linear birefringence results reported by Westphal et al. The elastic stiffness and compliance constants, CE11, CE44, and sE44 are also determined between 200 and 370 K.
TL;DR: The singular value decomposition technique is used to reconstruct the electronic spectral weight function for a half-filled Hubbard model with on-site repulsion U = 4t from quantum Monte Carlo data, finding a two-band structure for the single-particle excitation spectrum.
Abstract: The singular value decomposition technique is used to reconstruct the electronic spectral weight function for a half-filled Hubbard model with on-site repulsion U = 4t from quantum Monte Carlo data. A two-band structure for the single-particle excitation spectrum is found to persist as the lattice size exceeds the spin-spin correlation length. The observed bands are flat in the vicinity of the (0, pi), (pi, 0) points in the Brillouin zone, in accordance with experimental data for high-temperature superconducting compounds.