Directional dispersion of extraordinary phonons in layer compound InSe

The resonant Raman scattering of polar optical phonons has been measured in trigonal γ-InSe at the E'₁ exciton edge. The two-phonon scattering spectrum widely spreads over the frequency range of 50 cm^-1 with an extremely asymmetric lineshape. This spectrum has been interpreted in terms of the directional dispersion of extraordinary LO and TO phonons.     

High-temperature absorption coefficient of methane at 3.392μ

The spectral absorption coefficient of methane at 3.392μ has been measured in the temperature range 965 ?T, °K≤2710 behind incident and reflected shock waves. It is given by the relation P'=P'₀(T₀/T)ⁿ where P'₀=(1.34±0.58)x10²cm^-1atm^-1 at T₀=300°K and n=2.88±0.21. The empirically determined temperature exponent n may be approximately accounted for by a simplified theoretical analysis.     

Phase transitions in ferroelectric ceramics of the type Sr0.5Ba0.5Nb2O6

The ferro-paraelectric transition in Sr_0.5Ba_0.5Nb₂O₆ ceramics has been studied by measuring the dielectric pennitivity as a function of temperature at different frequencies. Experimental results in the transition region over ?'_max fit the relation $\text{1}\text{?'}\text{?}\text{1}\text{?'}{}_{\max }\text{= A(T ?}\text{T}{}_0\text{)}{}^{\mathrm{\gamma }}$ with γ > 1, as is typical for dif transitions. In an interval of temperatures of 17°C over T₀ (=Tfor?'_max), γ = 2. Using the relaxors' model of Kirillov-Isupov an equation is inferred in order to compute the activation energy of the relaxors as a function of parameters directly obtained from the experimental results.     

High resolution nonlinear spectroscopy. Dicke narrowing and dispersion of the third-order nonlinear susceptibility of H2 near the Q01 (1) vibrational resonance

The forward scattering process of motional narrowing in hydrogen gas has been investigated by an original method of nl spectroscopy of general application. The method has allowed a detailed study of the dispersion of the nl susceptibility χ⁽³⁾(ω) showing an unexpected behavior of χ⁽³⁾(ω)' near the Q₀₁ (1) molecular eigenfrequency.     

Collective excitations in the 1-D-ferromagnet CsFeCl3 with singlet ground state

By means of inalastic neutron scattering we have determined the dispersion relation of the magnetic excitations in CsFeCl₃ at different temperatures.The dispersion in c-direction, along the Fe-chains is typically ferromagnetic and in the hexagonal plane antiferromagnetic. Due to the lack of an applicable theory the data were parametrized by the simple heuristic formula:?ω = [2J[1 - cos πq_c] [A + 2J(1 - cos π)q_c)] + [C + J' (1.5 + γ(q))]²]^{$\text{1}\text{2}$}The gap was found to be C = 0.148 THz, the easy plane anisotropy A = 0.308 THz, the ferromagnetic interaction J = 0.148 THz and the antiferromagnetic interaction J' = -0.04 THz. At 1.25 K all excitations had a width smaller than the instrumental resolution ΔE = 0.025 THz. These results can be interpreted as follows: CsFeCl₃ is a singlet ground state system with strong ferromagnetic interaction J along the crystallographic c-axis and weak antiferromagnetic interaction J' in the plane perpendicular to c.In addition we have measured the influence of a magnetic field along the hexagonal c-axis. The splitting found agrees with the assumed level scheme yielding g = 2.5 for the first excited level.     

Landau damping: New aspects of an old story

We reinvestigate the dispersion relation for longitudinal plasma waves in a collisionless electron plasma. We show that even at finite temperature there exists a critical wave number k_cr below which Landau damping is absent. Furthermore, the magnitude of damping deviates from Landau's formula also well above k_cr. We propose to extend existing experiments to wave numbers k ～ k_cr.     

On the third order elastic constants of AgCl-AgBr mixed system

Lowdin's many body effect is accounted to explain the violation of Cauchy's relation (C₁₂=C₄₄) in silver halides. Lundqvists potential model with many body effect has been used to evaluate the third order elastic constants of AgCl and AgBr. A modified Lundqvist potential model is used to calculate the third order elastic constants for the simple AgCl- AgBr mixed system with varying concentration of AgCl and AgBr.     

Proprietes electroniques et electrogalvaniques du seleniure d'argent β: Domaine d'existence

A study of the electronic and electrogalvanic properties of β silver selenide has been performed on polycrystalline samples whose non-stoichiometry is controlled by eoulometric titration with the cell Ag/RbAg₄I₅/Ag_2+? Se/Pt. The adoption of an electronic model according to which the Frenkel defects of the silver sublattice are completely ionised allows us to compute independently the non-stoichiometry with the two formulaes δ = [Ag^o_i] ? [V'_Ag] and δ = n ? p. The homogeneity range has been drawn at positive temperatures and the formation enthalpy of the Frenkel defects is H'_F = 0,40 eV.     

An unconditionally stable time-domain discretization on cartesian meshes for the simulation of nonuniform magnetized cold plasma

In this paper an unconditionally stable, spatially and temporally implicit time-domain discretization for nonuniform magnetized cold plasma is developed. The discrete dispersion relation is free of spurious solutions and approximates the continuous dispersion relation for well-resolved wavelengths and frequencies (kΔ ? π, ωΔ_t ? π). For a specific choice of parameters, the discrete dispersion relation approximates the continuous dispersion relation for all wavelengths and frequencies up to the Nyquist limit. A few examples, amongst them one involving mode conversion, illustrate the new method.     

Generalized dielectric function and the plasmon-phonon coupling in GaAs and CdTe

Far infrared (12–235 cm^-1 reflectivity data for GaAs and CdTe have been fitted equally well with the usual two-oscillator dielectric function and Kukharskii's generalized form ?_K. Kukharskii's extended Lyddane—Sachs—Teller relation was confirmed and the quantities appearing in ?_K agreed fairly well with other determinations. ?_K was used to analyze the damped plasmon-phonon modes.     

Absorption intensities for vibration-rotation bands and the dipole-moment expansion of HBr

Line intensities in the four 0–2, 0–3, 0–4, 0–5 vibration-rotation bands of HBr were measured. The electric dipole matrix elements 〈0|M|ν'〉 for vibrational transitions with ν'?5 have been calculated by using a Dunham potential and the analytical solution of the Schrödinger equation described by R.H. Tipping. A dipole-moment expansion accurate to M₅ was determined by fitting these matrix elements to the available experimental data on line intensities. The experimental results were also used to calculate the Einstein coefficients of the R₀ lines for the bands ν' → ν′' with ? ν' ? 5.     

The symmetry properties of the normal vibrations of C-15 type superconductor HfV2

The symmetry species of the normal vibrations of HfV₂ are analysed. The symmetry vectors at Г, δ and X, and phonon dispersion ω(δ) are given. The irreducible representation Г'₂ is responsible for the structural transition O_h⁷ → C_2v²⁰.     

Resonant Raman scattering at higher M0 exciton edge in layer compound InSe

Resonant Raman spectra of γ-rich InSe have been measured at the absorption peak, E'₁, which lies 1.2 eV above the lowest direct gap. The resonance behaviors observed indicate that the E'₁ peak is due to the formation of damped M₀ excitons.     

Measurement of complex susceptibility on a metallic spin glass with broad relaxation spectrum

AC susceptibility measurements (0.625 H_z?_v?625 H_z) have been performed in a SQUID magnetometer on the amorphous metallic spin glass (Fe_0.06Ni_0.94)₇₅P₁₆B₆Al₃. The in-phase component of the susceptibility (x') shows a sharp peak at the spin glass freezing temperature T_g≈8 K with a frequency dependence of ?T_g/T_g≈0.015 per decade of frequency increase. The out-of-phase component (x″) exhibits a small anomaly at the spin glass transition with the magnitude of the anomaly almost independent of frequency. In particular we find the relation x″=(π;/2)?x'/? lnω to be valid in the vicinity of T_g. This relation and a frequency independence of x″ are fundamental characteristics of a spin glass having a broad spectrum of relaxation times. We argue that similar results from ac susceptibility measurements should be found in many spin glass systems, metallic as well as non-metallic.     

Magneto-optic phase shift in plasmon propagation along garnet/semiconductor-on-insulator structures

This paper discusses the magneto-optic phase shift in garnet/semiconductor-on-insulator plasmonic waveguides. We consider two structures: (1) Y IG/Si/SiO₂ and (2) Y IG/GaInAsP/AlInAs-oxide. A dispersion relation for the plasmon propagation has been derived and the nonreciprocal phase shift of the fundamental TM mode has been determined at wavelengths of 1.55 μm, 1.5 μm and 1.3 μm.     

Indirect exciton dispersion in III–V semiconductors: “Camel's back” in GaP

A new perturbation approach to exciton dispersion in indirect gap semiconductors is developed. For GaP and AlSb existence of the “camel's back” in exciton dispersion is confirmed, and a precise value of the “camel's back” parameter for X^c₁-minima in GaP is reported: E(X^c₁)?E_min(Δ^c₁)=3.5±0.3 meV. At the X-point the 21.44 and 19.48 meV exciton binding energies in GaP are obtained. The corresponding valley-anisotropy splitting is 1.96 meV.     

Spinel block doping and conductivity of sodium beta″-alumina ceramics

Sodium ion conducting fully stabilized, single phase β″-Al₂O₃ ceramics of compositions Na_1+z+2z'M_zLi_z'Al_11?z?z'O[in17, M=Mg or Ni, have been investigated. The conductivities of these ceramics do not depend upon the kind of stabilizing ions introduced into the spinel blocks, but predominantly depend upon the composition of the conduction slab. For fully magnesium stabilized ceramics with M=Mg and z′= 0, conductivity at 300°C is maximal for 3z = 2.0…2.2.     

The forced magnetostriction of nickel at 4.2 K

The forced volume magnetostriction of polycrystalline nickel at 4.2 K has been determined with a relative accuracy of 2 × 10^?2. Combining our result with previous data on the forced magnetostriction, we derive for the forced magnetostriction constants: h'₀ = (40 ± 1) × 10^?8T^?1, h'₁ = (-95 ± 2) × 10^?8T^?1, h'₂ = (-19 ± 2) × 10 ^?8T^?1.     

Direct experimental evidence of the hyperfine predissociation of molecular iodine using a saturated absorption experiment

A saturated absorption technique using an actively stabilized C.W. dye laser has been used to study the hyperfine structure of some lines lying in the 9-3, 10-3, 11-3, 11-4, 12-3 bands of the B-X system of molecular iodine. The comparison of the different spectra shows that the intensities of the different hyperfine components of one line deviate from the 2F + 1 proportionality when 'v decreases towards the value 'v=6 where the potential curves of the ³Π⁺₀ and 1u states are crossing. The preliminary experimental results concerning the hyperfine component intensity variations versus the quantum numbers 'v, J and F give a direct qualitative support to the recently reported hyperfine predissociation in I₂.     

Modified expression for permeability tensor in partially magnetised ferrites

Green and Sandy's experimental results [IEEE Trans Microwave Theory Tech.MTT-22 641 (1974)] for μ', the permeability tensor element of the partially magnetised ferrites, show systematic discrepancies with the values computed by them from their formula for large values of the normalised average magnetisation. It has been shown that a good agreement is possible if Schlömann's expression for μ'₀ occuring in this formula is replaced by another expression originally given by Sandy provided the average demagnetisation factor N of the domains is taken as a linear function of the magnetisation. This modification is also able to interpret the author's experimental results on Magneto-Microwave Kerr Effect successfully, which are not at all explained by the original Green and Sandy formula.