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1.
Summary It is shown that the upper polariton branch forB n=1 exciton (E‖e) crosses then=3, 4, ... branches for A-exciton (E∼c). It indicates the possibility of energy transfer between ordinary and extraodinary modes near the crossing (?isotropic?) points.  相似文献   

2.
The anisotropy of the optical properties of a single crystal of the hexagonal manganite HoMnO3 has been investigated by spectroscopic ellipsometry in the spectral range 0.6–5.0 eV. It has been demonstrated that the optical absorption edge for the polarization Ec is determined by the intense narrow transition O(2p) → Mn(3d) centered at 1.5 eV, whereas this transition for the polarization Ec is strongly suppressed and shifted toward higher energies by 0.2 eV. It has been revealed that, at the temperature T = 293 K, the spectra for both polarizations Ec and Ec exhibit a broad absorption band centered at ∼2.4 eV, which was earlier observed in nonlinear spectra during optical second harmonic generation.  相似文献   

3.
The effect of diffusion anisotropy of material particles in toroidal vortices (TVs) is experimentally studied in plasma TVs in air, in vortex rings in air and water. The essence of this effect consists in the fact that diffusion coefficients of material particles in TVs in the direction perpendicular to the rotation axis D are much lower than in the direction parallel to this axis D . The coefficient D is determined for propane molecules in air TVs, and the dependence of the coefficient D of ink particles in water TVs on the rotation angular velocity ω is studied. It is shown that the coefficient D can decrease with increasing ω by a factor of 10–25 in comparison with the coefficient D .  相似文献   

4.
Summary The spin-orbit structure ofF A centres in KCl:Li and KCl:Na have been studied by means of the magnetic circular dichroism. Due to theirC 4V symmetry theF A centres have two different spin-orbit parameters, Δ and Δ, which only in the KCl:Li case follow the relation: Δ < ΔF < Δ as expected from the theory. For a close comparison we have also reported our measurement of the spin-orbit coupling ofF centre in KCl. The spin-orbit parameters of theF andF A centres have been determined using the method of moment.  相似文献   

5.
Boltzmann-transport equation is analytically solved for two-component magnetoplasma using Chapman-Enskog analysis to include collisional diffusion transport having anisotropies in both streaming velocity and temperature components. The modified collisional integrals are analytically solved with flux integrals and perturbed kinetic equation to arrive at drift diffusion velocity and resulting transport coefficients which are markedly affected by both streaming and temperature anisotropy. The early isotropic results are recovered in the limit V 0 = 0 and T = T which reduce to eqs (11.30) and (11.31) of [1] and eqs (2.7) and (2.13) of [2]. The electrical resistivity (η) diminishes sharply in fusion temperature limit kT = 1 keV. The shape of the curves for both electrical resistivity and thermal conductivity is rectangular hyperbolic. However, for low thermal ratio (T /T < 1), the curves are raised up and for high thermal ratio (T /T > 1), they are lowered down the isotropic case (T /T > 1), showing comparatively diminished magnitudes of the quantities.   相似文献   

6.
B R Ratna  R Shashidhar 《Pramana》1976,6(5):278-283
The principal dielectric constants of the pentyl to octyl derivatives of 4′-n-alkyl-4-cyanobiphenyl have been measured as functions of temperature in their nematic and isotropic phases. All the compounds exhibit a strong positive dielectric anisotropy due to the presence of a large dipole moment along the major molecular axis. The principal dielectric constantsε andε as well as the anisotropy Δε decrease with increasing alkyl chain length. The experimental value of (ε+2ε) decreases with decreasing temperature, and is throughout less than the extrapolated isotropic value, in conformity with the model of antiferroelectric short range order proposed by Madhusudana and Chandrasekhar.  相似文献   

7.
The EPR spectra of Ce3+ impurity ions in LiYF4, LiLuF4, and LiTmF4 double-fluoride single crystals have been investigated at a frequency of ∼9.3 GHz in the temperature range 5–25 K. The effective g factors of the ground Kramers doublet of the cerium ions in three crystals are close to each other (g = 2.737, g = 1.475 for LiYF4:Ce3+). A superhyperfine structure of the EPR spectrum of Ce3+ ions in the LiTmF4 Van Vleck paramagnet has been observed in the external magnetic field B oriented along the crystallographic axis c (Bc). The superhyperfine structure of the EPR soectra of the Ce3+ ions in the LiYF4 and LiLuF4 diamagnetic matrices is resolved for Bc. Possible factors responsible for this pronounced difference in the properties of the systems studied have been discussed.  相似文献   

8.
A theory of μSR method is developed for uniaxial anisotropic high-T c superconductors. In two extreme cases ofH ext‖c andH ext⊥c analytical formulas are obtained which makes it possible to determine from the position of van Hove singularities in the Fourier-spectrum of muonium polarization, the type and parameters of the vortex lattice, such as λ ab c ). In caseH extH c2 we obtained the shape of the Fourier-spectrum in analytical form and the simple method of determining the Ginsburg-Landau parameter κ. Convenient expressions for numerical calculations are obtained for the arbitrary orientation of the external field, and an algorithm is provided to compute the mean fieldB, the vortex lattice parameters and the bulk field distribution in anisotropic superconductor. The Fourier spectrum of polarization based on these calculations can be used to independently check the validity of the high-T c parameters determination for “appropriate” orientations.  相似文献   

9.
Ellipsometric spectroscopy has been performed on nonpolar ZnO surfaces in the spectral range 1.5 eV<ħω<4.0 eV. Absolute measurements with two different crystal orientations in air allow the determination of the optical constantsn ,k andn ,k for light polarized parallel and perpendicular to thec-axis. The ellipsometric angles Δ and ψ are changed remarkably on ultrahigh vacuum cleaved surfaces near the band gap energy of ∼3.4eV when oxygen or atomic hydrogen is adsorbed or when the crystal is annealed. This observation is interpreted in terms of a field effect on the optical constants in the space charge layer.  相似文献   

10.
Standard μSR experiments in diamond have shown that the relative sign of the hyperfine parameters of the anisotropic Mu* state is negative (A /A <0). We report an experimental determination of theabsolute sign of the Mu* hyperfine parameters by studying the transferred muon polarization during the thermally-activated transition from the isotropic Mu state to Mu*. The results demonstrate that the isotropic part of the Mu* hyperfine interaction is negative. In a nitrogen-poor diamond, both the Mu disappearance rate and the enhancement of the Mu* signals are well-described by a single Arrhenius law.  相似文献   

11.
Summary Using Stahl's coherent wave approach we calculated the linear interband susceptibility near the band gap. The starting point was the ?MGM? formula with a smeared-out dipole densityM(r) and the Green's functionG for the effective-mass Hamiltonian with a screened Coulomb potential. The susceptibility so obtained was used for calculating transmission spectra of CdS platelets for energies near the so-called isotropic point lying far below the nearest excitonic resonance. By fitting experimental spectra we determined components of the residual dielectric tensor for polarization of the incident beam perpendicular and parallel to thec-axis, the mixed-mode dipole moment corresponding toB-exciton, and decay radii characterizing transition dipole densities. The established set of parameters determines the dielectric tensor for a quite wide energetic range.  相似文献   

12.
The nonlinear resistive properties of superconductors in the mixed state in the presence of a system of unidirectional planar defects (twins) have been investigated theoretically within the framework of the two-dimensional stochastic model of anisotropic pinning based on the Fokker-Planck equations with a concrete form of the pinning potential. These equations allow one to obtain an exact analytical solution of the problem. Formulas are obtained for experimentally observable even and odd (relative to reversal of the direction of the external magnetic field) nonlinear longitudinal and transverse magnetoresistivities ρ ‖,⊥ ± ( j,t,α,ε) as functions of the transport current density j, temperature t, the angle α between the directions of the current and the twins, and the relative volume fraction ε occupied by the twins. In light of the great variety of types of nonlinear resistive dependences contained in these expressions for ρ ‖,⊥ ± the most characteristic of them are presented in the form of graphs with commentary. The desired nonlinear dependences ρ ‖,⊥ ± are linear combinations of the even and odd parts of the function v(j,t, α,ε), which has the sense of the probability of overcoming the potential barrier of the twins; this makes it possible to give a simple physical treatment of the nonlinear regimes. New scaling relations for the Hall conductivity are obtained and investigated which differ from the previously known relations for isotropic pinning. The interaction of vortex motion directed along the twins and the Hall effect is considered for Hall constants which are arbitrary in magnitude and sign, and it is shown that in the case of small Hall viscosity vortex motion directed along the twins has an effect on the odd magnetoresistivities ρ and ρ , whereas the reverse effect can be neglected. It is shown that pinning anisotropy is sufficient to manifest the new nonlinear (in the current) magnetoresistivities ρ + and ρ . Zh. éksp. Teor. Fiz. 116, 2103–2129 (December 1999)  相似文献   

13.
A study of reflectance spectra from thin ZnSxSe1−x solid-solution layers in the region of excitonic resonances is reported. It has been found that an increase in sulfur concentration in the layers increases the inhomogeneous broadening of the quantized polariton lines. It has been established that the inhomogeneous line broadening in a reflectance spectrum depends on the magnitude of exciton-photon mixing; it is small in the long-wavelength region where the photon component of the polariton is large, and large at short wavelengths where the mechanical component dominates. Fiz. Tverd. Tela (St. Petersburg) 40, 867–868 (May 1998)  相似文献   

14.
15.
The spectrum and intensities of NMR lines are investigated experimentally and theoretically for excitation by an alternating magnetic field h‖ parallel to a static field H in the quasi-one-dimensional, six-sublattice antiferromagnet CsMnBr3. According to theory, two new NMR lines, which are not excited by a transverse magnetic field h , are observed near the phase transition from triangular to collinear structure (H=H c ) [JETP 86, 197 (1998)]. Zh. éksp. Teor. Fiz. 115, 2228–2241 (June 1999)  相似文献   

16.
Summary A complete polarization analysis of the GaS Raman spectrum, for excitation energies below the indirect energy gap, is reported. In order to assign second-order combinations and defect-induced forbidden modes, that appear in the spectra besides the six well-known Γ-phonons, also IR transmittance and reflectance measurements, for bothEc andEc, have been performed. All the available selection rules are applied to both Raman and IR data, allowing to identify the high-symmetry points of phonons involved in the scattering and, when possible, to ascribe the main non-Γ structures of the spectra to the knownK andM point modes. This analysis brings to several new attributions, also ruling out some previous assignments, based on the separate study of either Raman or IR spectra. Work partially supported by M.P.I.  相似文献   

17.
It is well known that the superconducting transition temperature of high-T c cuprates depends on the number of CuO2 planes in the unit cell. The multilayer structure implies the possibility of interlayer hopping. Under the assumption that the interlayer hopping can be specified by the parameter t (k) = t (cos(k x ) − cos(k y ))2, the quasiparticle excitation spectrum for the bilayer cuprate in the superconducting state has been determined in the framework of the tt′ − t″ − t J* model using the generalized mean-field approximation. It turns out that the interlayer hoppings does not create any additional mechanism of the Cooper paring and does not lead to an increase in T c . The splitting of the upper Hubbard quasiparticle band attributed to the interlayer hoppings is manifested as two peaks in the doping dependence of the superconducting transition temperature at temperatures below the maximum T c value for a single-layer cuprate. It has been found that antiferromagnetic interlayer correlations suppress the interlayer splitting. This probably leads to the common doping dependence of T c for both single-layer and bilayer cuprates.  相似文献   

18.
Muon spin relaxation (μSR) data taken at LAMPF on ac-axis oriented fine powder sample of YBa2Cu3O7−δ (YBCO) embedded in epoxy are analyzed for relaxation rate anisotropy. Clear differences beyond simple magnetic field penetration depth anisotropy are observed forBc andB c. The low-temperature anisotropy ratio is consistent with oriented ceramic data. Small crystallite size and anisotropic flux pinning characteristics are suggested as the fundamental cause of the additional effects.  相似文献   

19.
The Jahn-Teller effect in the ZnGa2O4 spinel single crystal has been investigated using electron paramagnetic resonance of Cu2+ ions in the temperature range 110–560 K. It has been shown that copper ions occupy octahedral sites 16d in the ZnGa2O4 crystal with cubic symmetry O h 7 (Fd-3m). At T < 560 K, the octahedra undergo tetragonal distortions (predominantly tension) and rotation around the fourfold axes by the angle θ ≈ 2.6°. The parameters of the spin Hamiltonian, which characterize the prolate (g = 2.355, g = 2.077, A = 116 Oe, A tp = 12 Oe) and oblate (g = 2.018, g = 2.246, A = 75 Oe, A = 44 Oe) octahedra, have been determined. At temperatures above 560 K, the static Jahn-Teller effect transforms into the dynamic effect and the spectrum of the magnetic resonance becomes isotropic with g = 2.116 (the experimental frequency corresponds to the X band).  相似文献   

20.
Room temperature EPR spectra of (NH4)2SO4 doped K2SO4 monocrystals irradiated with x-rays show the presence of NH3 + radicals. The EPR parameters areg ‖=2.0037 andg ⊥ = 2.0068;14NA XX=13.75;A YY=24.5;A ZZ=25.5 gauss;1HA XX=A YY=22 andA ZZ=25 gauss. From the14N and1H coupling constants it has been inferred that at room temperature the planar NH3 + radical undergoes rotation about theC 3 axis which corroborates with the equivalence of the protons, but the radical itself is in an asymmetric crystal field environment. The 77K spectra indicate a considerable reduction in the motion of the radical with the free motion almost completely stopped. Part of Ph.D. work of the second author  相似文献   

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