Showing papers on "Brillouin zone published in 1996"
TL;DR: A new sensing technique for the distributed measurement of temperature and strain, based on Brillouin optical frequency-domain analysis, is presented and the first experimental results demonstrate the feasibility of this new concept.
Abstract: A new sensing technique for the distributed measurement of temperature and strain, based on Brillouin optical frequency-domain analysis, is presented. Theoretical investigations and first experimental results of distributed measurements demonstrate the feasibility of this new concept.
236 citations
TL;DR: By the use of an iterative method the linearized phonon-Boltzmann equation for a dielectric solid subjected to a thermal gradient is solved and it is possible to calculate the thermal conductivity of rare-gas solids starting from the pair potential and accounting for the real Brillouin zone of the lattice.
Abstract: By the use of an iterative method the linearized phonon-Boltzmann equation for a dielectric solid subjected to a thermal gradient is solved in the frame of three-phonon interactions. In this way it is possible to calculate the thermal conductivity of rare-gas solids starting from the pair potential and accounting for the real Brillouin zone of the lattice. The numerical results are in full agreement with experiment and represent a considerable improvement with respect to those previously deduced for an isotropic solid.
213 citations
TL;DR: The influence of electron-electron scattering on quasiparticle lifetimes in graphite is calculated and the inverse lifetime increases linearly with energy, in agreement with recent experiments.
Abstract: The influence of electron-electron scattering on quasiparticle lifetimes in graphite is calculated. In the limit when the Fermi surface is reduced to isolated points in the Brillouin zone, the suppression of screening leads to deviations from conventional Fermi liquid behavior. The inverse lifetime increases linearly with energy, in agreement with recent experiments. Similar features should also be present in narrow gap semiconductors and in carbon nanotubes.
201 citations
TL;DR: In this article, the SBS threshold of a fiber with Brillouin frequency shift distribution along its length is investigated theoretically and experimentally, and a simple equation for estimating the sBS threshold from the effective gain coefficient, which is calculated by using the frequency distribution along the length of the fiber.
Abstract: The SBS threshold of a fiber with Brillouin frequency shift distribution along its length is investigated theoretically and experimentally. We obtain a simple equation for estimating the SBS threshold from the effective gain coefficient, which is calculated by using the Brillouin frequency distribution along its length. The dopant concentration dependence of the Brillouin frequency shift are measured for fibers with an F and GeO/sub 2/ codoped silica core. The evaluated frequency shift per unit of dopant concentration is 277 MHz/wt% and 45 MHz/wt% for F and GeO/sub 2/, respectively, at 1.55 /spl mu/m. The SBS threshold of a fiber with a nonuniform Brillouin frequency shift distribution prepared by the VAD method is investigated experimentally. The fiber exhibits 7 dB improvement in its SBS threshold. This value is in good agreement with one estimated by calculating the effective gain coefficient. This simple equation will be useful for estimating the SBS threshold of various fibers.
172 citations
TL;DR: In this article, the virtual gap states (ViGS) of complex semiconductor band structure are derived from the Brillouin zone and their character varies from predominantly donor-like closer to the valence band to mostly acceptor-like nearer to the conduction band.
Abstract: The band lineup at metal–semiconductor contacts as well as at semiconductor heterostructures may be described by one and the same physical concept, the continuum of interface‐induced gap states. These intrinsic interface states derive from the virtual gap states (ViGS) of the complex semiconductor band structure and their character varies from predominantly donorlike closer to the valence band to mostly acceptorlike nearer to the conduction band. Calculations are presented of the respective branch points for elemental and binary as well as ternary compound semiconductors which make use of Baldereschi’s concept of mean‐value points in the Brillouin zone [Phys. Rev. B 7, 5212 (1973)], Penn’s idea of dielectric band gaps [Phys. Rev. 128, 2093 (1962)], and the empirical tight‐binding approximation (ETB). The results are as follows. First, at the mean‐value point the band gaps calculated in the GW approximation have the same widths as the dielectric band gaps. Second, the ETB approximation reproduces the GW va...
149 citations
TL;DR: Inelastic neutron scattering is used to measure the spin wave dispersion throughout the Brillouin zone of the double-exchange ferromagnet La0.7Pb0.3MnO3 and yields unusual broadening of the high frequency spin waves, even within the ferromagnetic phase.
Abstract: We use inelastic neutron scattering to measure the spin wave dispersion throughout the Brillouin zone of the double-exchange ferromagnet La0.7Pb0.3MnO3. Magnons with energies as high as 95 meV are directly observed and an unexpectedly simple Heisenberg Hamiltonian, with solely a nearest-neighbor coupling of 8.79 +/- 0.21 meV, accounts for the entire dispersion relation. The calculated Curie temperature for this local moment Hamiltonian overestimates the measured Curie point (355 K) by only 15%. Raising temperature yields unusual broadening of the high frequency spin waves, even within the ferromagnetic phase.
144 citations
TL;DR: In this article, it was shown experimentally that the ratio of the intensities of Rayleigh and Brillouin backscattered light (Landau Placzek ratio) in an optical fiber has a temperature dependence which may be used for the basis of a distributed temperature sensor.
130 citations
TL;DR: In this article, a finite difference method is developed to analyze the guided-wave properties of a class of two-dimensional photonic crystals (irregular dielectric rods) for both in-plane and out-of-plane propagation.
Abstract: In this paper, a finite difference method is developed to analyze the guided-wave properties of a class of two-dimensional photonic crystals (irregular dielectric rods). An efficient numerical scheme is developed to deal with the deterministic equations resulting from a set of finite difference equations for inhomogeneous periodic structures. Photonic band structures within an irreducible Brillouin zone are investigated for both in-plane and out-of-plane propagation. For out-of-plane propagation, the guided waves are hybrid modes; while for in-plane propagation, the guided waves are either TE or TM modes, and there exist photonic bandgaps within which wave propagation is prohibited. Photonic bandgap maps for squares, veins, and crosses are investigated to determine the effects of the filling factor, the dielectric contrast, and lattice constants, on the band-gap width and location. Possible applications of photonic bandgap materials are discussed.
124 citations
TL;DR: A dark lattice of atoms in dark atomic ground states is a promising system to observe periodic excursion across the Brillouin zone in a uniform force field.
Abstract: Atoms in dark atomic ground states do not interact with the laser light present and are therefore not susceptible to spontaneous processes. Laser cooling populates these states. Confinement of atoms in dark states in a (periodic) gauge potential allows for a lattice of atoms with a very low decay rate, a dark lattice. A dark lattice is a promising system to observe Bloch oscillations of neutral atoms, i.e., periodic excursion across the Brillouin zone in a uniform force field.
102 citations
TL;DR: Inelastic neutron-scattering experiments have been performed on a single crystal of a compound with a spin fluctuation spectrum that is broad in energy and strongly correlated in wave vector, with maximum intensity at the Brillouin zone boundary as mentioned in this paper.
Abstract: Inelastic neutron-scattering experiments have been performed on a single crystal of $({\mathrm{Y}}_{0.97}{\mathrm{Sc}}_{0.03}){\mathrm{Mn}}_{2}$. The spin fluctuation spectrum is broad in energy and strongly correlated in wave vector, with maximum intensity at the Brillouin zone boundary. There is no magnetic scattering for Brillouin zones centered at the origin and at certain reciprocal lattice points, suggesting the existence of short-lived 4-site collective spin singlets. The unusual features of the dynamical susceptibility discovered in this experiment result from geometrical frustration and give new insight into the heavy-fermion-like behavior of the compound.
101 citations
01 Jan 1996
TL;DR: In this article, Bloch oscillations of atoms in the fundamental energy band of a periodic optical potential were measured under the influence of a constant inertial force for various potential depths.
Abstract: The early quantum theory of electrical conductivity in crystal lattices by Bloch and Zener [1,2] led to the striking prediction that a homogeneous static electric field induces an oscillatory rather than uniform motion of the electrons. These so-called Bloch oscillations have never been observed in natural crystals because the scattering time of the electrons by the lattice defects is much shorter than the Bloch period. In semiconductor superlattices the larger spatial period leads to a much shorter Bloch period (,600 fs) and Bloch oscillations have recently been observed through the emission of THz radiation by the electrons [3]. Here we present Bloch oscillations of atoms in the fundamental energy band of a periodic optical potential. We directly measure the atomic momentum distribution evolving in time under the influence of a constant inertial force for various potential depths. We experimentally observe oscillation periods in the millisecond range as well as positive and negative effective masses. Bloch oscillations are a pure quantum effect which can be explained in a simple one-dimensional model. The periodicity of the lattice (period d) leads to a band structure (Fig. 1) of the energy spectrum of the particle and the corresponding eigenenergies Ensqd and eigenstates jn, ql (Bloch states) are labeled by the discrete band index n and the continuous quasimomentum q; Ensqd and jn, ql are periodic functions of q with period 2pyd and q is conventionally restricted to the first Brillouin zone g2pyd, pydg [4]. Under the influence of a constant external force F, weak enough not to induce interband transitions, a given Bloch state jn, qs0dl evolves (up to a phase factor) into the state jn, qstdl according to qstd qs0d 1 Ftyh . (1) This evolution is periodic with a period tB hyjFjd corresponding to the time required for the quasimomentum to scan a full Brillouin zone. The mean velocity in jn, qstdl
TL;DR: In this paper, a k-point sampling scheme is proposed, which is computationally efficient and its efficacy relative to other common approaches is demonstrated. But it is shown that the use of a single sampling point at the origin of reciprocal space is especially inefficient.
Abstract: Brillouin-zone sampling in total-energy calculations of aperiodic systems using periodic boundary conditions is considered. Although the energies converge to the exact result in the limit of large supercells for any k-point sampling scheme, they do not converge at the same rate. In particular, it is shown that the use of a single sampling point at the origin of reciprocal space is especially inefficient. A k-point sampling scheme is proposed, which is computationally efficient and its efficacy relative to other common approaches is demonstrated.
TL;DR: A quantum field theory for nonuniform spin configurations is derived within a coherent state path integral approach and external fields can be used to interpolate continuously between the Bloch wall dispersions for half-integer and integer spin.
Abstract: We study spin parity effects and the quantum propagation of solitons (Bloch walls) in quasi-one-dimensional ferromagnets. Within a coherent state path integral approach we derive a quantum field theory for nonuniform spin configurations. The effective action for the soliton position is shown to contain a gauge potential due to the Berry phase and a damping term caused by the interaction between soliton and spin waves. For temperatures below the anisotropy gap this dissipation reduces to a pure soliton mass renormalization. The quantum dynamics of the soliton in a periodic lattice or pinning potential reveals remarkable consequences of the Ferry phase. For half-integer spin, destructive interference between opposite chiralities suppresses nearest-neighbor hopping. Thus the Brillouin zone is halved, and for small mixing of the chiralities the dispersion reveals a surprising dynamical correlation. Two subsequent band minima belong to different chirality states of the soliton. For integer spin the Ferry phase is inoperative and a simple tight-binding dispersion is obtained. Finally it is shown that external fields can be used to interpolate continuously between the Bloch wall dispersions for half-integer and integer spin.
Journal Article•
TL;DR: In this article, the lattice dynamics of CaSi03 perovskite were investigated and it was shown that the ground-state structure is a distorted phase with lower than cubic symmetry.
Abstract: ABsTRACI' First-principles linear-response calculations were used to investigate the lattice dynamics of what is thought to be the third most abundant phase in the lower mantle, CaSi03 perovskite. The commonly assumed cubic structure (Pm3m) was found to be dynamically unstable at all pressures, exhibiting unstable modes along the Brillouin zone edge ftom the M point to the R point. On the basis of these results, we predict that the ground-state structure of CaSi03 perovskite is a distorted phase with lower than cubic symmetry. We predict that a phase transition occurs in CaSi03 perovskite within the Earth's lower mantle from the low-temperature distorted phase to the high-temperature cubic phase. The predicted phase transition possibly explains some of the seismologicalobservations of reflective features within the lower mantle.
TL;DR: It is shown that a linear coupling of orthorhombic strain to one of the modes at \ensuremath{\Gamma} plays a role in the discussion of the possibility of this phase transition, and no mechanical instabilities (soft modes) are found, either at £Gamma or at any of the other high-symmetry points of the Brillouin zone.
Abstract: A first-principles study of the vibrational modes of ${\mathrm{PbTiO}}_{3}$ in the ferroelectric tetragonal phase has been performed at all the main symmetry points of the Brillouin zone (BZ). The calculations use the local-density approximation and ultrasoft pseudopotentials with a plane-wave basis, and reproduce well the available experimental information on the modes at the \ensuremath{\Gamma} point, including the LO-TO splittings. The work was motivated in part by a previously reported transition to an orthorhombic phase at low temperatures [(J. Kobayashi, Y. Uesu, and Y. Sakemi, Phys. Rev. B 28, 3866 (1983).] We show that a linear coupling of orthorhombic strain to one of the modes at \ensuremath{\Gamma} plays a role in the discussion of the possibility of this phase transition. However, no mechanical instabilities (soft modes) are found, either at \ensuremath{\Gamma} or at any of the other high-symmetry points of the BZ. \textcopyright{} 1996 The American Physical Society.
TL;DR: Brillouin light scattering is utilized to investigate the magnetic properties of the hexagonal-close-packed as well as the body- and face-centered cubic phases of elemental cobalt stabilized as thin epilayers and the implications towards the understanding of magnetic property of itinerant ferromagnets are discussed.
Abstract: We utilize Brillouin light scattering to investigate the magnetic properties of the hexagonal-close-packed as well as the body- and face-centered cubic phases of elemental cobalt stabilized as thin epilayers. Expressions for the dependence of the surface and bulk magnons on applied magnetic field and in-plane propagation direction yield the exchange stiffness constant D, saturation magnetization M, and magnetic anisotropy fields of the cobalt atoms synthesized in these distinct crystal structures. Estimates of D and M are also calculated from the electronic band structure for the different crystalline phases. Satisfactory agreement is found between theory and experiment. The implications of these results towards our understanding of magnetic properties of itinerant ferromagnets are discussed. \textcopyright{} 1996 The American Physical Society.
TL;DR: The complete spectrum of the double spinon excitation in the spin-Peierls system CuGe${\mathrm{O}}_{3}$ is mapped as a function of temperature for the first time.
Abstract: The complete spectrum of the double spinon excitation in the spin-Peierls system CuGe${\mathrm{O}}_{3}$ is mapped as a function of temperature for the first time. The spin dynamics of the lower boundary and the excitation continuum evolve quite differently. Moreover, the dimerization of the lattice produces a sharp excitation in the lower energy boundary at the edge of the Brillouin zone, as well as the well known spin-gap opening at the zone center.
TL;DR: Optical transmission measurement on two similar two-dimensional triangular lattices of air rods with different lattice constants has revealed that the central frequencies of photonic band gaps show a reasonable shift relative to each other, providing firm evidence for the existence of a common gap for H polarization in the entire 2D Brillouin zone.
Abstract: Optical transmission measurement on two similar two-dimensional (2D) triangular lattices of air rods with different lattice constants of the order of 1.0 \ensuremath{\mu}m has revealed that the central frequencies of photonic band gaps show a reasonable shift relative to each other. The respective gap frequencies observed in the 1.02-\ensuremath{\mu}m lattice are found to be consistent with the theoretical ones. These two facts provide firm evidence for the existence of a common gap for H polarization in the entire 2D Brillouin zone. \textcopyright{} 1996 The American Physical Society.
TL;DR: In this article, a Monte Carlo study of the high-field electron transport in 4H-SiC is presented using a new analytic band model, which consists of two analytical bands that include band bending at the Brillouin zone boundaries.
Abstract: A Monte Carlo study of the high‐field electron transport in 4H–SiC is presented using a new analytic band model. The band model consists of two analytical bands that include band bending at the Brillouin zone boundaries. The band bending is very important in 4H–SiC and 6H–SiC and has to be taken into account in order to have an accurate model at high electric fields. Numerical calculation of the density of states given by the new model has been used in order to model the energy dependence of the scattering mechanisms accurately. The new model predicts a lower saturation velocity in the c direction (peak velocity 1.8×107 cm/s) than in perpendicular directions (peak velocity 2.1×107 cm/s). This is directly related to the strong band bending in the c direction. This effect is also responsible for a much more pronounced velocity peak in the c direction compared to perpendicular directions. In the low‐field region the mobility is higher in the c direction (mobility ratio near 0.8), which is in agreement with experimental results.
TL;DR: In this article, an angle resolved photoemission study of a surface state on the SiC(0001)-(√3 × √3) surface is reported, and the results indicate that Si adatoms on top of an outermost SiC bilayer may be an inadequate structural model for explaining recent experimental findings for the Si c(0001) surface.
TL;DR: In this article, high-resolution angle-resolved photoemission spectroscopy (ARPES) measurements of the noncuprate layered perovskite superconductor Sr2RuO4 were presented.
Abstract: We present high-resolution (HR) angle-resolved photoemission spectroscopy (ARPES) measurements of the noncuprate layered perovskite superconductor Sr2RuO4. ARPES spectra of the whole valence-band region obtained along two high-symmetry directions in the Brillouin zone show clear dispersion, generally similar to that of a band calculation. However, HRARPES measurements taken in the vicinity of the Fermi level (E(F)) show narrower Ru4d epsilon(xy,yz,zx)-O2p pi antibonding bands than those predicted by the band calculation. More significantly, there is an extended van Hove singularity very close to E(F) (E(B)=11 meV) along the Ru-O bonding direction, which is known to exist in cuprate high-temperature superconductors. The Fermi-surface topology obtained by HRARPES (one electronlike Fermi surface sheet centered at the Gamma point and two holelike sheets centered at the X point) is different from the band calculation (two electronlike sheets centered at the Gamma point and one holelike sheet centered at the X point), although the electron count is the same in both cases. These results suggest that electron-electron correlations cause the modification of the Fermi-surface topology, and is thus necessary for understanding the electronic structure and properties of Sr2RuO4.
TL;DR: Using a nearly-free-electron model, the origin of a Brillouin-zone-dependent intensity variation for equivalent valence states is identified, i.e., states which are related by reflection through a (010)-type Bragg plane and which lie close to such a plane.
Abstract: We model photoelectron angular distributions obtained earlier by Himpsel et al. [Phys. Rev. Lett. 68, 3611 (1992)] for the F 2p bands in LiF(100). The F 2p states are treated within a many-body, quasiparticle approach, and a nearly-free-electron model is presented for the description of conduction-band states relevant to the photoemission process. In the quasiparticle results, we find a band gap of 14.4 eV and a F 2p bandwidth of 3.6 eV, in satisfactory agreement with experimental values of 14.2 and 3.5 eV for these respective quantities. A method for computing photoelectron angular distributions is presented, followed by a comparison of simulated and measured photoelectron angular distributions for several parts of the three-dimensional Brillouin zone. In this comparison, constant-energy contours in the F 2p bands are clearly portrayed in both theoretical and experimental images. Using the model, we also identify the origin of a Brillouin-zone-dependent intensity variation for equivalent valence states, i.e., states which are related by reflection through a (010)-type Bragg plane and which lie close to such a plane. \textcopyright{} 1996 The American Physical Society.
TL;DR: Christenson and Lau as discussed by the authors showed that a small amount of dissipation, caused by current flow in a lossy external circuit, can produce a disruption of steady-state cycloidal electron flow, leading to the establishment of a turbulent steady state that is close to, but not exactly, Brillouin flow.
Abstract: It is shown that a small amount of dissipation, caused by current flow in a lossy external circuit, can produce a disruption of steady‐state cycloidal electron flow in a crossed‐field gap, leading to the establishment of a turbulent steady state that is close to, but not exactly, Brillouin flow. This disruption, which has nothing to do with a diocotron or cyclotron instability, is fundamentally caused by the failure of a subset of the emitted electrons to return to the cathode surface as a result of resistive dissipation. This mechanism was revealed in particle simulations, and was confirmed by an analytic theory. These near‐Brillouin states differ in several interesting respects from classic Brillouin flow, the most important of which is the presence of a microsheath and a time‐varying potential minimum very close to the cathode surface. They are essentially identical to that produced when (i) injected current exceeds a certain critical value [P. J. Christenson and Y. Y. Lau, Phys. Plasmas 1, 3725 (1994)...
TL;DR: In this paper, the authors reported the results of a first-principles LAPW calculation of the equation-of-state, dynamic stability, and infrared-active transverse optic vibrational mode frequencies of CaSiO3 perovskite.
Abstract: We report the results of a first-principles LAPW calculation of the equation-of-state, dynamic stability, and infrared-active transverse optic vibrational mode frequencies of CaSiO3 perovskite. A Birch-Murnaghan fit to the computed energy-volume relation of the cubic phase yields values of Vo=45.62 A³, Ko=227 GPa, and Ko′=4.29 for the thermally-corrected equation-of-state parameters. These values are in excellent agreement with recent quasi-hydrostatic compression data to 10 GPa, but significantly differ from values derived from higher pressure non-hydrostatic compression data. We calculate the volume dependence of the infrared-active TO mode frequencies using a frozen-phonon approach. The lowest frequency ferroic mode is predicted to occur near 228 cm−1 at ambient pressure and displays classic soft-mode behavior in the tensile regime, in quantitative agreement with earlier molecular and lattice dynamical calculations, based on empirical potentials. These established a link between the low frequency ferroic mode and the thermally activated crystalline-amorphous transition in a model CaSiO3 perovskite system. Our present calculations also reveal that the static cubic perovskite structure is unstable with respect to small octahedral rotations, corresponding to Brillouin zone edge dynamical instabilities, at ambient pressure and throughout the pressure range of the lower mantle. We speculate that coupling of the low frequency ferroic mode with octahedral tilting modes and strain lower the activation energy for the crystalline-amorphous transition.
TL;DR: In this paper, the authors performed optical transmission and synchrotron small-angle x-ray scattering (SAXS) experiments on colloidal crystals with optical refractive index ratios as large as possible over a wide range of volume fractions.
Abstract: We have performed optical transmission and synchrotron small-angle x-ray scattering (SAXS) experiments on colloidal crystals with optical refractive index ratios as large as possible over a wide range of volume fractions. These conditions push colloidal crystals into the regime where strong coupling of photonic crystals with light occurs. The optical transmission spectra reveal minima corresponding to stop gaps on the edges of the Brillouin zone of the photonic band structures. The positions of the optically measured stop gaps agree well with lattice spacings measured by SAXS. The stop gap in the 111 direction of crystals of polystyrene in water has a width of up to 5% of the gap frequency as a function of volume fraction, in agreement with theoretical band-structure calculations. A maximum of the relative width confirms the notion that the strength of the interaction between photonic crystals and light has an optimum as a function of volume fraction. The detailed structural information from SAXS data greatly assists in the interpretation of optical experiments on photonic crystals.
TL;DR: Spin gap behavior of CaV4O9 is studied by including the effects of frustrating magnetic interactions and lattice distortions and its effect on the uniform susceptibility and the spin gap are explored.
Abstract: Spin gap behavior of CaV4O9 is studied by including the effects of frustrating magnetic interactions and lattice distortions. The spectrum of triplet excitations is calculated for a Heisenberg model on the 1/5-depleted square lattice. In the spin gap phase, the location of the minima of the spectrum in the Brillouin zone is found to depend nontrivially on the exchange parameters. Experimental consequences of the temperature-dependent lattice distortion including its effect on the uniform susceptibility and the spin gap are explored.
TL;DR: In this paper, the elastic constants of acoustic and optic phonons were determined by Brillouin scattering as a function of the stoichiometry, and the C44 elastic constant was shown to be a clear minimum for the [Li]/[Nb]=1 in the melt sample.
Abstract: Acoustic and optic phonons have been measured by Brillouin and Raman spectroscopies in LiNbO3 samples with different stoichiometries. Consequently, the elastic constants have been determined by Brillouin scattering as a function of the stoichiometry. The C44 elastic constant presents, as a function of the stoichiometry, a clear minimum for the [Li]/[Nb]=1 in the melt sample. This behavior must be related to the existence and competition of two kind of defects, i.e., extended defects induced when growing samples not at the congruent composition, and point defects present in nonstoichiometric samples. The optic phonons seem to be dominated by the point defects. The linear increase of the phonon lifetimes, with respect to an ideal stoichiometric sample, can be due to the scattering by the static imperfections and to an increase of the anharmonic scattering. Several Raman peaks, which appear when the [Li]/[Nb] ratio decreases, are related to the presence of Nb in antisites. The width of some particular phonon...
TL;DR: In this paper, the exchange coupling in Fe whisker/Cr/nFe specimens, for n=10, 20, 30, and 40 ML, showed no obvious dependence on the Fe layer thickness, and the measured change in the phase of the short wavelength oscillations, the presence of a slowly varying exchange coupling bias, and small measured values of exchange coupling are caused by the same mechanism: interface alloying.
Abstract: Angular resolved Auger electron studies were carried out for Fe whisker/Cr(001) interfaces which were prepared at 100, 180, 246, and 296 °C. The Cr atoms penetrate progressively into the second (counting from the surface) atomic layer at 100, 180, and 246 °C. At 296 °C the Cr atoms enter the third atomic layer. No noticeable fraction of the Cr atoms was found in the fourth atomic layer. The exchange coupling was studied in Fe whisker/Cr/Fe(001) films which were grown in a nearly perfect layer by layer mode. Magneto‐optic Kerr effect and Brillouin light scattering measurements showed that the measured change in the phase of the short wavelength oscillations, the presence of a slowly varying exchange coupling bias, and the small measured values of exchange coupling are caused by the same mechanism: interface alloying. The exchange coupling in Fe whisker/Cr/nFe specimens, for n=10, 20, 30, and 40 ML, showed no obvious dependence on the Fe layer thickness.
TL;DR: The magnitude of the bilinear and biquadratic interlayer coupling strengths between Fe layers separated by Cr spacer layers is investigated by means of Brillouin light scattering, magneto-optic Kerr rotation, and magnetoresistance techniques, and a data analysis scheme yields self-consistent anisotropy and inter layer coupling parameters extracted independently from the three techniques.
Abstract: The magnitude of the bilinear and biquadratic interlayer coupling strengths between Fe layers separated by Cr spacer layers is investigated by means of Brillouin light scattering, magneto-optic Kerr rotation, and magnetoresistance techniques. A data analysis scheme, which treats all three data sets on an equal footing, yields self-consistent anisotropy and interlayer coupling parameters extracted independently from the three techniques. The values of the bilinear and biquadratic coupling strengths are compared for simultaneously grown (211) and (100) Fe/Cr samples. The approach not only provides reliable values for the coupling strengths but also highlights the complementarity of these techniques in uniquely determining the magnetic parameters. \textcopyright{} 1996 The American Physical Society.
TL;DR: In this paper, the performance of an SBS suppression fiber with a non-uniform dopant concentration along its length fabricated by the VAD method was investigated and it was shown that the increase in the SBS threshold can be estimated from the ratio of the Brillouin frequency shift change over the effective interaction length to the intrinsic gain bandwidth.
Abstract: We have investigated experimentally the performance of an SBS suppression fiber with a nonuniform dopant concentration along its length fabricated by the VAD method. We have achieved an SBS threshold of 15 dBm against a continuous wave at 1.55 /spl mu/m. This is 7 dB larger than that of conventional fiber. We have confirmed experimentally that the increase in the SBS threshold can be estimated from the ratio of the Brillouin frequency shift change over the effective interaction length to the intrinsic Brillouin gain bandwidth. Moreover, we have confirmed that there is no BER degradation after a transmission of 138 km through a 2.5 Gb/s intensity modulation direct detection system when the SBS suppression fiber is used with an input power of 16 dBm.