The longitudinal magnetophonon effect in semiconductors containing magnetic impurities

The dependence of longitudinal magnetoresistance on magnetic field in semiconductors containing magnetic impurities is investigated theoretically. The calculation takes into account the scattering of electrons on magnetic impurities and on optical phonons. The inelastic optical phonon scattering itself is responsible for magnetophonon oscillations of the magnetoresistance, the extremes of these oscillations occuring when energy distance between Landau levels is equal to the energy of optical phonon, $\text{h}\text{?}$ω₀. The scattering on magnetic impurities may lead to spin flip electronic transitions. The spin flip electronic transitions manifest themselves as additional minima on the oscillatory picture of magnetoresistance. These new minima occur when the energy separation between spin-split Landau levels is equal to $\text{h}\text{?}$ω₀.     

Resonant interaction of acceptor states and optical phonons in silicon

The resonance broadening of line 2 in the excitation spectrum of gallium acceptors in silicon due to near coincidence of its energy with that of the zone center optical phonons, $\text{h}\text{?}$ω₀, has been confirmed under significantly improved experimental conditions. An additional feature labeled X and line 2 are interpreted as mixed excitations of the bound-hole and the optical phonon. Under uniaxial stress, the stress induced components of line 2 which approach $\text{h}\text{?}$ω₀ become more phonon-like and get “pinned” while the components of X become bound-hole-like as they recede from $\text{h}\text{?}$ω₀, and exhibit a striking increase in intensity.     

NMR in single crystal metallic ferromagnets: GdAl2

Necessary conditions to observe NMR in wall-free metallic single crystal ferromagnets are formulated. ²⁷Al NMR study in a magnetized single crystal GdAl₂ confirms the validity of the preconditions. Improved resolution and control over orientation, both inherent to single crystal study, enable for the first time an angular dependent NMR measurement of hyperfine interaction in metallic ferromagnetic system. The significance of the measured hyperfine tensor $\text{A}\text{?}\text{(A}{}_{\mathrm{\chi \chi }}\text{/λ}\text{h}\text{?}\text{= A}{}_{\mathrm{yy}}\text{/λ}\text{h}\text{?}\text{= - 14.825}\text{kG}$; $\text{A}{}_{\mathrm{zz}}\text{/gl}\text{h}\text{?}\text{= - 15.313}\text{kG}$) is briefly discussed.     

Infrared hole burning in matrix-isolated 1,2-difluoroethane with a tunable diode laser

Infrared hole burning within the absorption profile of the ν₁₇ vibrational transition of 1,2-difluoroethane matrix-isolated in solid Ar, Kr, and N₂ was observed. These measurements allowed the determination of the homogeneous and inhomogeneous linewidth ($\text{Δ}\text{ν}\text{?}{}_{\mathrm{<mtext>h</mtext>}}\text{= 0.002}\text{cm}{}^{\mathrm{?1}}$ at 2.5 K in Kr, $\text{Δ}\text{ν}\text{?}{}_{\mathrm{<mtext>i</mtext>}}\text{= 0.25}\text{cm}{}^{\mathrm{?1}}$). The temperature dependence of the homogeneous linewidth is explained in terms of vibrational relaxation as well as dephasing processes. A detailed analysis of the changes in the absorption profile with irradiation and calculation of the potential energy surface for rotation of the molecule in the matrix cage suggest a reorientation of the molecules in the matrix to be the cause of the observed hole burning.     

Brillouin study of acoustic phonon softening and optical absorption coefficients of ultraheavily doped n-Si

The self-energies of acoustic phonons in ion implanted and laser annealed ultraheavily doped n-type Si have been measured by Brillouin scattering. The corresponding softening of the elastic constants has been estimated from the observed phonon softening and compared it with theory. At high doping levels ($\text{N}{}_{\mathrm{e}}\text{≧ 10}{}^{21}\text{cm}{}^{-3}$) the effect of the increase in atomic mass on the phonon frequency is observed in the case of doping with As. From the increase in the linewidths of the Brillouin lines with doping, the optical absorption coefficients for $\text{λ = 5145}\text{A}\text{?}$ as a function of doping are determined.     

Exciton binding energy in GaAs quantum wells deduced from magneto-optical absorption measurement

Magneto-optical absorption spectra due to exciton states and Landau-levels were measured in GaAs/AlAs multi-quantum-wells. By extrapolating the photon energies of the absorption peaks to zero magnetic field, the lowest state (1S) heavy hole exciton binding energy, E^B_$\text{h}$(1S), was obtained as a function of well size L_z in the range $\text{58}\text{A}\text{?}\text{?}\text{L}{}_{\mathrm{z}}\text{?252}\text{A}\text{?}$. The L_z dependence of E^B_h showed the change of the exciton character from three-dimensional to two-dimensional with decreasing L_z. The diamagnetic shift observed for the heavy hole exciton peak was larger than that for the light hole exciton peak, showing the anisotropic nature of the Luttinger-Kohn Hamiltonian. The diamagnetic shift of the heavy hole exciton peak became smaller as L_z was decreased, suggesting the enhancement of the two-dimensional exciton character.     

Electron diffraction and infrared study of the semimetallic layered compound Ti1−xVxSe2

The crystals of the system Ti_1?xV_xSe₂ (C ≤ x ≤ 0.05) undergo a second order structural phase transition. Electron diffraction studies show that the transition temperature decreases with progressive V-doping. The phase transition considerably affects the infrared reflectivity, measured at 300 and 77 K in the spectral range 40 cm^?1 to 4000 cm^?1.The presence of free carriers and the existence of optical infrared active E_u phonon modes $\text{(}\text{E}\text{⊥}\text{c}\text{)}$ confer their characteristic appearance to the spectra. At room temperature one phonon structure is measured at 143 cm^?1. At 77 K a new series of phonon peaks appears up to a V-concentration of 5 % as a direct consequence of superlattice formation.At room temperature the plasma-edge shifts towards higher frequencies as the vanadium concentration increases. This effect is caused by a large increase of $\text{N}\text{m}{}^1$, associated with the mixing of impurities. It is indicative of the small density of states at the Fermi level in semimetallic TiSe₂. Our results suggest a phase transition driven by lattice dynamical effects.     

Self-consistent cranking calculations for 20Ne

The rotational spectrum of ²⁰Ne has been calculated in the self-consistent cranking model using the Skyrme interaction. The qualitative features of the spectrum, e.g., the band cutoff at $\text{J = 8}\text{h}\text{?}$, are reproduced. The inclusion of states of the oscillator f-shell in the expansion of the single-particle states leads to a transition to an excited band for $\text{J > 8}\text{h}\text{?}$. Special emphasis is put on an investigation of the structural properties near and beyond this band cutoff at $\text{J = 8}\text{h}\text{?}$. The calculated rotational spacings are found to be considerably too small with all conventional variants of the Skyrme interaction. The difficulty is attributed to the p-state part of the Skyrme interaction.     

Electron-phonon interaction in superconducting Nb

Acoustic phonon damping in Nb due to superconductivity is accurately measured by the inelastic neutron scattering technique. The phonon line widths can be characterized by the reduced parameters $\text{h}\text{?}\text{ω}{}_{\mathrm{p}}\text{/2Δ(0)}$ and T/T_c, and are in good qualitative agreement with the calculation by Bobetic based on the BCS theory.     

Structural changes within the plastic phase of diamantane

Structural changes within the pre-melting plastic phase of diamantane have been revealed from high-temperature X-ray powder diffraction data. A gradual transition to a more disordered state is suggested, and hexagonal symmetry ($\text{a = 14.1}\text{A}\text{?}\text{, c = 11.0}\text{A}\text{?}$) for the plastic phase is firmly established.     

Study of the photoluminescence spectrum in high purity CdTe

In this work, a study of the photoluminescence produced by a high purity sample of n-type CdTe of $\text{?}\text{N}{}_{\mathrm{<mtext>D</mtext>}}\text{?}\text{N}{}_{\mathrm{<mtext>A</mtext>}}\text{? < 10}{}^{14}$ impurities per cm³ was done at several temperatures, varying from 10 to 35 K. Several sharp lines were observed in the spectral region between 1.5 to 1.6 eV, plus the well-known 1.4 eV band with several well-defined structures on it. The observed temperature behaviour of the line positions, linewidths and relative intensities allowed us to establish the presence of a new transition, located at 10 K 21.3 meV below in energy from the free exciton (FE) line, as well as its first phonon replica. Its nature seems to be transitions originating from the conduction band to an acceptor level, 32 meV above the valence band. These two lines appear at the same position where previous works had reported the first and second phonon replicas of the FE. A scheme of impurity level is proposed to explain the observed transitions in terms of previously established levels and this new acceptor level.     

Separation of overlapping singlet and triplet band systems in Cl2CS by LFES and MRS techniques

The visible absorption band systems of Cl₂CS have been reexamined using laser fluorescence excitation and magnetic rotation spectroscopy. Since the former is sensitive only to S₁ ← S₀ transitions and the latter primarily to T₁ ← S₀ transition, the spin multiplicities of the features in the overlapping singlet and triplet systems could be unambiguously determined. Analyses of the spectra gave new values for ν′₆ = 189 cm^?1 in the $\text{A}\text{?}$ state and ν′₁ = 923 cm^?1 in the $\text{a}\text{?}$ state. Bands with types A and C polarization were found to occur only very weakly in the $\text{A}\text{?}\text{←}\text{X}\text{?}$ spectrum in marked contrast to the corresponding system in the prototype thiocarbonyl compound, H₂CS.     

High-spin states in 208Rn

The yrast decay scheme of ²⁰⁸Rn has been investigated up to spin $\text{≈ 20}\text{h}\text{?}$ and an excitation energy of ≈ 6 MeV. Several different γ-ray spectroscopic techniques were used to determine the properties of excited states and transitions in the nucleus. Significant changes to the previously established level scheme are proposed, based on the existence of an unobserved 3.1 keV transition. Simple empirical shell-model calculations of level energies aided in the assignment of shell-model configurations to excited states and the decay scheme is discussed in terms of these configurations. The energy level systematics for the even radon isotopes, from A = 206 to 212 are discussed, as are core polarization effects in the even radon isotopes (A = 204 to 210) and polonium isotopes (A = 202–208).     

The accommodation of trivalent gold in Silver Chloride

Gold-doped silver chloride annealed in a chlorine atmosphere at 300°C is shown to contain precipitates of AgAuCl₄, a compound not previously reported. The substance melts at 265 ± 2°C and has a monoclinic unit cell with $\text{a = 11.124 ± 0.008}\text{A}\text{?}$, $\text{b = 4.105 ± 0.002}\text{A}\text{?}$, $\text{c = 6.539 ± 0.006}\text{A}\text{?}$ and β = 93.11 ± 0.05°. Its optical absorption spectrum is discussed and the method of precipitate formation in silver chloride is described in terms of an internal oxidation type of process.     

Microscopic theory on the Raman spectra of transition metal dichalcogenides in CDW state

Microscopic mechanisms are clarified for Raman scattering of collective modes, i.e., amplitude and phase modes in the charge density wave (CDW) state of transition metal dichalcogenides. We study three phonon process in triple CDW state and effects of $\text{partial}$ destruction of the Fermi surface due to the phase transition. It has then been understood how both phase and amplitude modes are given Raman activity and how A-E splittings of both modes and the commensurability pinning of the phase mode are related to the three phonon process. We can also explain change of Raman intensity of the originally Raman active A_1g phonon mode at phase transition as interference between paramagnetic and diamagnetic contributions for 2HTaSe₂ as well as other materials.     

Nuclear matrix elements in the first-forbidden β-decay of 125Sb

Nuclear matrix elements in the $\text{7}\text{2}$⁺(444 keV β^?)$\text{9}\text{2}$^?(177 keV γ)$\text{11}\text{2}$^? β-γ cascade in have been extracted from the available experimental data. A significant cancellation in the Coulomb-enhanced matrix element combination permits good limits of error to be placed on the individual matrix elements, even though there is not a large amount of experimental data available.     

Loss of ferromagnetism in YNi3 after H2 absorption

The compound YNi₃ ($\text{PuNi}{}_3\text{-}\text{type}\text{,}\text{a}\text{= 4.973}\text{A}\text{?}\text{,}\text{c}\text{= 24.42}\text{A}\text{?}$) is ferromagnetic below T_c = 35 K. After hydrogen absorption it loses its ferromagnetic character and becomes Pauli paramagnetic. The composition of the ternary hydride is approximately YNi₃H₄. The lattice constants are $\text{a}\text{= 5.267}\text{A}\text{?}$, $\text{c}\text{= 26.57}\text{A}\text{?}$.     

Dipole moment function and vibration-rotation matrix elements of HCl35 and DCl35

The infrared intensity measurements and molecular beam electric resonance dipole moment measurements for HCl and DCl have been reviewed. A method not previously exploited is used to determine infrared matrix elements from the electric resonance dipole moment measurements. A ‘best’ set of matrix element values was selected for HCl and from these the M_i-coefficients of a polynomial dipole moment approximation were determined; M₀ = 1.0935±0.0007 D, $\text{M}{}_1\text{= 0.947±0.023 D/}\text{A}\text{?}$, $\text{M}{}_2\text{= 0.015±0.041 D/}\text{A}\text{?}{}^2$, $\text{M}{}_3\text{= -0.814± 0.116 D/}\text{A}\text{?}{}^3$. Calculations using this dipole moment function for both HCl and DCl are shown to give good agreement with available band strength and vibration-rotation interaction factor measurements. RKR potentials are also calculated for both molecules.     

Etude Cristallographique Et Magnetique De Fe2GeS4 Structures Magnetiques A 85 Et 4,2°K

Fe₂GeS₄ crystallizes in the orthorhombic space group Pnma; the cell parameters are: $\text{a = 12,467}\text{A}\text{?}$, $\text{b = 7,213}\text{A}\text{?}$, $\text{c = 5,902}\text{A}\text{?}$; the crystal structure is isotype with olivine.A magnetic study by the extraction method shows that Fe₂GeS₄ is paramagnetic until 108°K, then antiferromagnetic until 69°K and finally antiferro- and ferrimagnetic at lower temperatures.Neutron diffraction reveals the magnetic structures at 85 and 4,2°K and explains the anisotropy transition at 69°K.     

nπ1 Transitions in tetramethyl-1,3-cyclobutanedithione-h12 and -d12

The polarized low-temperature crystal absorption spectra of tetramethyl-1,3-cyclobutanedithione-h₁₂ and -d₁₂ have been measured in the visible region, and $\text{nπ}{}^1$ excited states identified as follows: ³A_u with origin ($\text{h}{}_{12}\text{d}{}_{12}$) at $\text{16 829}\text{16 836}\text{cm}{}^{\mathrm{?1}}$; ¹A_u and ¹B₁₀ with nearly degenerate origins near 18 000 cm^?1; and probably ¹A_u and ¹B_1g near 19 500 cm^?1. The singlet excited states lie close together and perturb each other strongly. As in the corresponding dione, $\text{CH}\text{CD}$ stretching vibrations of the substituent methyl groups are active in intensity borrowing, and the effects of excitation are delocalized over the entire molecule.