bluuebunny/crossref_metadata_2025 huggingface dataset:
Electron Paramagnetic Resonance of the Mn Cluster in Silicon
Authors: Kreissl J. , Gehlhoff W.
Published: July 2007

In high‐resistivity p‐type and n‐type silicon doped with manganese the Mn cluster is identified by EPR. The spectrum shows a characteristic hyperfine structure and an angular dependence of fine structure at 20 K. The analysis of the spectrum yield the assumption of the following cluster model: the cluster consists of four Mn0 atoms on nearest interstitial sites; it has cubic/tetrahedral symmetry; spin multiplets with S = 0, 1, 2, 3, 4, 5, and 6 are produced by a dominant exchange coupling where the multiplet with S = 6 is the ground state observed by the EPR experiments. The photo‐EPR results suggest a donor level (Mn4)0/+ near midgap.
The Substitutional Shallow Donor Size Effect
Authors: Grinberg M.
Published: July 2007

The influence of lattice deformation in the nearest neighbourhood of the impurity on the energy of localized states is investigated. The deformation potential and the energy contributions up to square of dilation are obtained for the shallow donors. As an example the donors in ZnSe are considered.
Superconductor—Semiconductor Transition in BaPb1−xBixO3
Authors: Hidaka M. , Fujii H. , Horie Y. , Mase S.
Published: July 2007

The origin of superconductor—semiconductor transition in BaPb1−xBixO3 is studied from the structural and dielectric properties obtained by measurements of the energy‐dispersive X‐ray diffraction, piezoelectric resonance, electric capacitance, and (D—E) hysteresis loop. The transition is clearly characterized by a rapid vanishing tendency of some characteristic temperatures associated with the above‐mentioned properties in the semiconductor region toward the limiting bismuth composition x ≈ 0.35.
Magnetic Relaxation in the Heisenberg Spin Glass
Authors: Schreiber J. , Schulz D.
Published: July 2007

On the basis of a dynamical theory for Heisenberg spin glasses the isothermal magnetic relaxation R(t) = M(t)/H after switching off a magnetic field H at t = 0 is calculated. The extreme short time relaxation shows an exponential decay with a temperature dependent relaxation time τ(T) and is essentially influenced by many‐body quantum effects in the spin glass state. An estimation of the long time relaxation yields in the qualitative agreement to experimental investigation a non‐exponential behaviour R(t) ∼ t−1/γ, where γ = 2 in an intermediate time region is found for T ≦ Tf. This anomalous relaxation is caused by a broad distribution of relaxation times owing to a distribution of local fields.
Decay Kinetics of UV Luminescence from Undoped PbCl2 Crystals
Authors: Polák K. , Birch D. J. S. , Nikl M.
Published: July 2007

The kinetics of the UV luminescence from PbCl2 crystals are measured from 3.8 to 25 K. Two components in UV luminescence are found. The form of the long time component of the UV luminescence decay curve is thoroughly investigated and compared with theoretical predictions. A model based upon exciton—exciton annihilation leading to free electron—hole pairs is used to describe the decay at temperatures above 15 K.
The Melting Laws
Authors: Kumari M. , Dass N.
Published: July 2007

It is shown that Simon's melting law is not a mere empirical relation but is based on the theoretical concepts of Lindemann. Thus, for the first time, Simon constants are identified correctly in term of the physical properties of the concerned solid. Moreover, it is shown that the other melting laws as given by Kennedy, Reynold et al. and Dass et al. follow well from it. The calculations of the melting temperature, Tm, are done in the case of argon and sodium chloride. Good agreement is found in each case.
Interaction Between Two Surface Excitations in Degenerate Polar Semiconductors
Authors: Srivastava K. S. , Sinha Achla , Srivastava Reena , Tandon Ajay
Published: July 2007

A systematic study of the interaction of surface plasmons with surface optical phonons is made for III–V group polar semiconductors to find the factors which can influence the coupling between the two modes of vibrations. It is found that the extent of coupling depends upon the Szigeti effective charge or the ionicity of the compound.
Indirect Nuclear Spin Interaction in Ferromagnets. Highest Approximation
Authors: Bokuchava G. G. , Buishvili L. L. , Tugushi A. I.
Published: July 2007

The problem of obtaining the nuclear spin interaction Hamilton operator via magnon field in ferromagnets is discussed by consecutive canonic transformation method. Using this method the one magnon nuclear spin interaction in any order of perturbation theory is taken into account. The indirect spin interaction Hamilton operator constant obtained is compared with the well known Suhl‐Nakamura interaction constant. It is shown, that in the second order of perturbation theory these results coincide.
On the Probability of Recoilless Absorption f′ and Reemission f″ in Some Fe‐Containing Compounds
Authors: Angelov V. , Bonchev Ts. , Rusanov V. , Mandjukov I.
Published: July 2007

The recoilless absorption probability f′ and the probability f″ of recoilless reemission after absorption are measured for four Fe‐containing compounds. It is established that f″ > f′. This discrepancy has already been observed for 119Sn. The results obtained disagree with the commonly accepted assumption that f′ and f″ are equal. The interpretation of this inequality is made in terms of two relaxation models.
On the Multipole Character of the X‐Ray Transitions in the Pre‐Edge Structure of Fe K Absorption Spectra. An Experimental Study
Authors: Dräger G. , Frahm R. , Materlik G. , Brümmer O.
Published: July 2007

The K absorption edge of pure Fe and the pre‐edge Fe K absorption of FeS2 (pyrite), Fe2O3 (hematite), and FeCO3 (siderite) are investigated with single crystal absorbers of these materials using linearly polarized synchrotron X‐radiation. From the angular dependence of the pre‐edge K absorption the existence of predominantly ligand‐field‐induced dipole transition in Fe2O3 and of quadrupole transitions in FeCO3 is concluded. The multipole character and the mechanism of the pre‐edge K absorption are discussed.
Excitons at High Density in CdS and GaSe, and Optical Bistability
Authors: Dneprovskii V. S. , Furtichev A. I. , Klimov V. I. , Nazvanova E. V. , Okorokov D. K. , Vandishev U. V.
Published: July 2007

Changes in the absorption and refractive index caused by laser absorption in CdS and GaSe are investigated and used to produce absorptive resonatorless bistability in CdS and to explain dispersive optical bistability in a GaSe Fabry‐Perot cavity.
A MREI Model for the Zincblende‐Like Phonons in the Mixed Defect Chalcopyrite ZnGa2(SxSe1–x)4
Authors: Lottici P. P.
Published: July 2007

Results are given on the compositional dependence of the optical phonon frequencies in the pseudoternary defect chalcopyrite mixed crystals ZnGa2(SxSe1–x)4 over all the composition range. The compositional variation of the TO and LO highest frequency polar zincblende‐like phonons is explained in terms of a MREI (modified random element isodisplacement) model.
Simplest Properties of Guided Wave Polaritons in Three‐Layer Structures
Authors: Burshta I. I. , Venger E. F. , Pasechnik Yu. A. , Snitko O. V.
Published: July 2007

The properties of guided‐wave polaritons of E‐ and H‐types are studied both, theoretically and experimentally. It is shown, that the interaction of an electromagnetic wave with film and substrate lattice oscillations changes the field spatial structure, ranges of existence, and dispersion dependences of surface excitations, i.e. of optical guided wave modes. Expressions describing the frequency dependences of attenuation and absorption factors of guided wave polaritons are received. It is shown that the course of these dependences is determined by peculiarities of the energy distribution between the system layers.
Ground State and Electronic Properties of Silicon Carbide and Boron Nitride
Authors: Van Camp P. E. , Van Doren V. E. , Devreese J. T.
Published: July 2007

The results of ab‐initio calculations of the ground state and electronic properties of the IV‐IV and III–V compounds, SiC and BN, are presented. These properties are derived from the total ground state energy of the crystal calculated in the local density approximation and from the one‐Particle Kohn‐Sham equations. The ab‐initio norm‐conserving non‐local pseudopotential of Bachelet, Hamann, and Schlüter is used. The bulk modulus, its pressure coefficients, and the pressure coefficients of the electron energy differences between the top valence band and lowest conduction bands are also derived. The results are compared with the few existing measurements and with calculations by other investigators.
Stimulated Emission of the I1 – TA (PM) Band in CdS
Authors: Hönig T. , Gutowski J.
Published: July 2007

In CdS, a strong transverse‐acoustic phonon replica of the acceptor–exciton recombination line I1 is observable. This band is called I1 – TA or PM band. Under high excitation desities, the I1 – TA shows a stimulated emission behavior, which leads to laser activity under suitable arrangements. By means of excitation spectroscopy, this behavior is shown to be strongly correlated with the creation of acceptor–exciton complexes (A0,X) in their ground and excited electronic states. Thus, the I1 – TA is not only unambiguously demonstrated to be an efficient recombination channel of acceptor–exciton complexes but also offers an excellent possibility to realize a four‐level bound‐exciton laser in CdS. This emission band is a valuable object to deepen the study of excited states of bound excitons in semiconductors under the use of high excitation densities.
Soliton Generation in Semi‐Infinite Molecular Chains
Authors: Brizhik L. S. , Gaididei Yu. B. , Vakhnenko A. A. , Vakhnenko V. A.
Published: July 2007

A mechanism for generating solitons in semi‐infinite molecular chains by exciting the impurity molecules is considered. The generation criteria of solitons are found and their dependence on molecular chain parameters, the input place, and localization degree of initiating excitation. The possibility to govern the generation efficiency and solitons velocity by changing the parameters of exciting singal is pointed out.
Vibrational Structure of Hydrogenated Amorphous Silicon Carbide Alloys
Authors: Ghosh B. K. , Agrawal Bal K.
Published: July 2007

Theoretical investigations of the various vibrational modes induced by hydrogen atoms in amorphous silicon carbide are made using a cluster Bethe lattice method (CBLM). The calculated results are in good agreement with available infrared data. Some theoretically calculated peaks need experimental verification.
Thermal Conductivity of Amorphous Si at Low Temperatures
Authors: Pompe G. , Hegenbarth E.
Published: July 2007

Measurements of thermal conductivity of amorphous Si films from 2 to 50 K are presented. The qualitative and quantitative behaviour is similar to thermal conductivity of other amorphous dielectrics. The temperature range of the plateau of λ(T) correlates with the maximum Tm = 30 K of the function c/T3(T). An analysis of the effective free path of phonons in dependence on the reduced temperature T/θD results in a remarkable coincidence for amorphous As, Se, Si, Ge, and SiO2, GeO2 in the plateau range. This fact leads to a restriction of hypotheses for explanation of the plateau of thermal conductivity at amorphous materials.
The Pressure Effect on the Phase Diagrams of the GeSn and SiSn Systems
Authors: Soma T. , Kamada K. , Kagaya H.‐Matsuo
Published: July 2007

The pressure effect on the phase diagrams of the GeSn and SiSn systems is studied using the previous electronic theory based on pseudopotentials and considering the α–β phase transition under pressure. The calculated results predict the appearance of the α‐phase solid solution for the GeSn system under pressure. The obtained curves near the melting point under pressure are shown for the GeSn and SiSn systems.
Cylindrical Quantum Well with Position‐Dependent Mass
Authors: Pérez‐Alvarez R. , Parra‐Santiago J. L. , Pajón‐Suarez P.
Published: July 2007

Using the envelope function approximation and a one band model, the cylindrical quantum well with position‐dependent mass problem is studied. The boundary conditions to be fulfilled by the radial wave functions are deduced. The transcendental equation for the energy levels, the normalised wave functions, and the confinement are obtained in the flat band approximation considering a sectionally constant mass profile. Also numerical results for the GaAsAl0.32Ga0.68As cylindrical quantum well are reported.
Surface Modes of a Type II Semiconductor Superlattice
Authors: Yonashiro K. , Tomoyose T. , Yamshiro M. , Kobayashi M.
Published: July 2007

The surface excitations are investigated in the three‐medium system of an ionic crystal, vacuum, and a type II semiconductor superlattice by making use of Maxwell's equations. The dispersion relations for the plasmon–optical phonon coupled modes are obtained on the interface between these two materials. The surface modes are discussed in detail in both, the high‐ and low‐frequency regions for the weak coupling limit.
Frequency‐Dependent Solution of the Time‐Dependent Hartree‐Fock Equation in the Electron Gas
Authors: Brosens F. , Devreese J. T.
Published: July 2007

A numerical procedure is presented to solve the time‐dependent Hartree‐Fock equation for the homogeneous electron gas. This equation accounts for the dynamical exchange effects in the dielectric function. The analytical and numerical techniques are described, and a comparison is made with the results of a variational approach, developed earlier. In general, the variational localfield correction turns out to be in good agreement with the (exact) numerical results. But the logarithmic singularities in the variational calculation are shown to be an artefact of the variational procedure, and not an inherent property of the dynamical exchange effects.
On the Static Dielectric Constant and Plasmon Energy of TiS2 and TiSe2
Authors: Oliveira L. E.
Published: July 2007

A simple extreme‐tight‐binding scheme is proposed to evaluate the long‐wavelength dielectric constant and main plasmon energy of the titanium dichalcogenide compounds TiS2 and TiSe2.
Conductivity and Dielectric Constant of Interacting Anderson Localized Systems at T = 0
Authors: Chicón R.
Published: July 2007

The electrical conductivity as a function of frequency at zero temperature is calculated for a system of interacting electrons with strongly localized wave functions due to disorder. The calculations are concentrated on the contribution from resonant phononless absorption by singly occupied pairs at low frequencies, where the Coulomb gap in the density of states is important. The static dielectric constant is also obtained using the Kramers‐Kronig relations.
Effect of Broadening of Tail States on the Einstein Relation in Heavily Doped Compensated Semiconductors
Authors: Ghosh S. , Chakravarti A. N.
Published: July 2007

An attempt is made to study the dependence of the Einstein relation on carrier concentration in heavily doped compensated semiconductors with broadened tail states, both in the presence and absence of a quantizing magnetic field, taking n‐InSb as an example. It is found that, corresponding to a given free electron concentration, the broadening of the tail states modifies the Einstein relation by enhancing the diffusivity–mobility ratio in the absence of magnetic quantization while the reverse is observed in the presence of a quantizing magnetic field. Besides, the rate of decrease of the ratio with increasing magnetic field in the quantum limit is found to be independent of such broadening effects.
Intrinsic Pinning in Superconductors with Extremely Small Coherence Lengths
Authors: Schimmele L. , Kronmüller H. , Teichler H.
Published: July 2007

By means of a Ginsburg‐Landau‐type theory which takes into account the discrete lattice structure the variation of the energy (“Peierls potential”) of an isolated flux line is calculated when shifted relatively to the crystal lattice. In particular, a primitive cubic lattice is considered with a straight flux line, aligned parallel to a cube axis. The resulting Peierls potential may lead to intrinsic pinning if the coherence length is smaller than about two nearest neighbour distances. The coherence lengths at low temperatures determined for the recently discovered high Tc superconductors of the YBa2Cu3O7 class come very close to this value so that intrinsic pinning might possibly be relevant for these superconductors.
Application of the Embedded Atom Method to Phonon Dispersions and Local Surface Vibrations in Copper
Authors: Luo Ningsheng , Xu Wenlan , Shen Shuechu
Published: July 2007

A formula of force constants between planes in lattice dynamics is derived from a new model within the framework of the Embedded Atom Method (EAM), which is based on results from density‐functional theory. Semiempirical functions for the description of the interaction properties in the ground state of Cu are determined by means of the EAM. Finally, force constants between planes of Cu, which lead to agreement between the obtained phonon dispersions and local surface vibrations and experimental results, may be calculated.
Plasma Waves in Degenerate Electron Systems with Random Impurities
Authors: Van Trong Nguyen
Published: July 2007

Propagation of plasma waves in degenerate electron systems is considered. A modified dispersion equation for plasma waves is derived by taking into account the influence of random impurities without using perturbation theory. The damping of plasma waves is calculated for the T = 0 limit. It is shown that the damping is non‐zero in long wavelength limit due to the random impurities.
Thermoelectric Properties of p‐Hg1−xCdxTe
Authors: Höschl P. , Moravec P. , Belas E. , Franc J. , Grill R.
Published: July 2007

Low temperature (77 to 300 K) thermoelectric measurements of undoped and well characterized p‐Hg1−xCdxTe (x ≈︁ 0.2) samples are reported. Analysis of the thermoelectric power is suggested on the basis of a three acceptor level model with one divalent acceptor (Hg‐vacancy) and one monovalent acceptor (foreign atom). From the temperature at which reversal of sign of the thermoelectric power takes place the concentration of holes at 77 K may be simply determined. The method is also suitable for the investigation of homogeneity of wafers of Hg1−xCdxTe with x ≈︁ 0.2.
Exact Solutions of Few First Passage Problems in Linear Correlated Walks. Applications to the Electron Trapping in a Semiconductor
Authors: Godoy S. , Fujita S.
Published: July 2007

The average number of steps, 〈N〉, in which a walker gets trapped at the origin when he starts at one of L − 1 non‐trap sites on a looping linear lattice of L points, is calculated for an arbitrary correlation. It is given by 〈N〉 = (L/6(1 + δ)) [(1 − δ) L + 1 + 5δ], where δ = α − β is the degree of correlation with α and β respresenting step probabilities for forward and direction‐changing motion, respectively. This result and others are obtained by solving basic difference equations for linear correlated walks with the aid of Fourier‐Laplace transformation techniques. Potential applications of the theory to trappings of electrons in a semiconductor and others are discussed.
EPR of V4+ in Apophyllite
Authors: Vassilikou‐Dova A. B. , Lehmann G.
Published: July 2007

In a natural apophyllite two crystallographically inequivalent centers of V4+ with triclinic point symmetries are observed. The more intense one is assigned to the Ca sites. Superhyperfine splitting due to one F nucleus is evident for many orientations, but a large portion of V4+ is evidently coordinated to an OH group replacing F. The less intense center is assigned to K sites in agreement with results of an earlier publication for a specimen from a different locality. Due to large linewidths its spectra were incompletely resolved. Both centers must arise from replacement of one water molecule by the oxygen of a VO2+ ion.
The Coherent Pairing and Bose‐Einstein Condensation of Excitons in Semiconductors
Authors: Bobrysheva A. I. , Moskalenko S. A. , Shvera Yu. M.
Published: July 2007

The possibility of particle and pair Bose‐Einstein condensation in a system of four species of excitons with different values of spin projections of the electron and of the hole is studied. It is known that the system has the following properties: 1) the interaction of the exciton of either type with all the exciton species is repulsive on the average; 2) the pairs of excitons with antiparallel spins of electrons as well as of holes interact attractively and biexcitons can be formed. In two limiting cases when the exciton–exciton interaction energy W is greater or smaller than the ortho–para‐exciton splitting Δ, it is shown that: 1. the coherent pairing of excitons with momenta k and −k coincides with Bose‐Einstein condensation of biexcitons with zero translational momentum. Such a state persists without collapse due to the internal spin structure of excitons. 2. In the system of para‐ and ortho‐excitons the Bose‐Einstein condensation of para‐excitons and biexcitons formed by two ortho‐excitons with zero total spin can take place simultaneously.
Picosecond Kinetics of Luminescence in Highly Excited Direct‐Gap Semiconductors
Authors: Klochikhin A. A. , Razbirin B. S. , Nelson D. K. , Amand T. , Brousseau M. , Collet J. , Cornet A. , Pugnet M.
Published: July 2007

Experimental and theoretical investigations of luminescence spectra kinetics are carried out in CuI, CdS, and CdSe crystals at concentrations below the Mott threshold. The observed radiation is shown to be due to exciton‐phonon‐plasmon interaction caused by the coexistence of excitons and an electron‐hole plasma (EHP) during the time interval shorter than the time, necessary for the EHP to undergo the transition into the gas of excitons. It is found that the inhomogeneous distribution of excitons and EHP is developing in a crystal despite the initially homogeneous excitation. Theoretical lineshape analysis of exciton‐phonon‐plasmon luminescence is shown to be able to provide information of its spatial distribution.
The Dispersion Relations of the Nonlinear Surface Waves Due to the Exciton and Biexciton Formation
Authors: Khadzhi P. I. , Kiseleva E. S.
Published: July 2007

Nonlinear surface waves (NSW) are considered taking into account both, the exciton‐photon interaction and the exciton‐biexciton conversion. Two different types of NSW solutions for the longitudinal component of the electric field Ex are obtained: monotonous and nonmonotonous ones. Dispersion laws are obtained and disussed for each type of the NSW solutions.
Effect of Magnetic Field on 3A1u → 1A1g Luminescence of Pb2+ in CaF2 and SrF2 and of Au− in NaCl
Authors: Overberg A. , Fischer F.
Published: July 2007

The magnetic field dependence of the zero‐phonon line intensity I0 and of the lifetime of the 3A1u → 1A1g emission is measured between LHeT and LNT. It is found that I0 prop. B2 up to 2.37 T. In NaCl:Au− already at this field strength the emission is completely π‐polarized. The structured phonon sidebands are strongly changed in the B field. Reciprocal lifetime versus B2 follows a straight line with a slope nearly independent of temperature. The results are discussed in analogy to those obtained on Pb2+ an Bi3+ alkaline‐earth chalcogenides.
Final State Core Level Shifts in Supported and Free Metal Particles
Authors: Castellani N. J. , Leroy D. B.
Published: July 2007

The final state contribution to core level electron binding energy shifts is analysed in the case of small free and supported particles. The results of a pseudopotential–electron gas linear response model that was developed in a preceding paper are compared with other jellium models (atom‐in‐jellium vacancy DFT, semi‐classical). As small particles are generally supported as clusters, the support contribution is also calculated, considering a possible charge transfer. Total relaxation contribution is then compared with the experimental results of Kohiki for the Pd/SiO2 system. Good agreement is obtained in the range 10 to 40 at. units.
Size‐Quantum Effect of the Energy of a Charge Carrier in a Semiconductor Crystallite
Authors: Pan J. S. , Pan H. B.
Published: July 2007

The size‐quantum effect of the energy of a charged carrier in a spherical semiconductor crystallite embedded in another spherical dielectric layer is discussed and the interaction of the charged carrier with surface optical (SO) and longitudinal optical (LO) vibrations is taken into account. In the first‐order approximation of the energy the charged carrier does not interact with SO vibrations, and it interacts only with LO vibration of the dielectric in which the charged carrier is located. The interaction energy between the charged carrier and LO vibrations will increase with decreasing the size of crystallite.
Theory of Electron Emission from Solids by Proton and Electron Bombardment
Authors: Rösler M. , Brauer W.
Published: July 2007

Using the microscopic theory of kinetic ion‐induced electron emission (IIEE) and secondary electron emission (SEE) developed earlier an improved description of transport processes of excited electrons is given. Electron–electron scattering rates are calculated including the dynamic screening of the Coulomb interaction. The resulting enhancement of these scattering rates compared with the Thomas‐Fermi approximation leads to new statements concerning the magnitude of contributions from different excitation mechanisms. The theory is applied to polycrystalline aluminum. For the proton‐induced electron emission the primary energies are limited to 20 to 800 keV and for the SEE to 1 to 2 keV. Compared to the other excitation mechanisms the excitation of single conduction electrons for IIEE (H+ → Al) and the excitation from inner shells for SEE produces the largest contribution to the yield, respectively. A better agreement between theory and experiment is achieved for both emission phenomena.
Dye‐Laser 4f–4f‐Line Probing of Crystal‐Field Fluctuations in ZnS:Sm3+ Polycrystalline Films
Authors: Löbe K. , Boyn R.
Published: July 2007

Using the dye‐laser site‐selective excitation technique, a study is made of 4G5/2 → 6H9/2, 6H7/2 inter‐Stark level transitions for a special type of Sm3+ centers in ZnS polycrystalline films. It is found that the emission lines become narrowed compared with the case of “nonselective” excitation, with the peak positions and intensities depending on the location of the dye‐laser energy within the 4f–4f excitation line profiles. The results can be quantitatively described by a simple model which involves small centre‐to‐centre fluctuations of crystal‐field parameters. A comparison with the (much sharper) lines measured for the same type of Sm centers in ZnS bulk crystals shows that these fluctuations have a Gaussian distribution with maximum corresponding to the bulk crystal situation. An explanation can be given on the basis of random strain originating from high dislocation densities. A discussion is made of whether the linewidths are affected by interactions between the Sm centres and by electric fields due to dislocation charge.
A Simple Scheme for Studies of Surface Phonons of Covalent Semiconductors. I. Calculation of Force Constants
Authors: Lin Zijing , Wang Kelin
Published: July 2007

A framework is given for calculating and interpreting vibrational surface properties of covalent semiconductors. The bond orbital approximation (BOA) in a tight‐binding theory for electronic structural energies is developed and applied to deriving atomic force constants that are essential for calculating dynamical matrix and phonon dispersion relations in these systems. The method used connects force constants with electronic structure directly and is able to predict phonon spectra as well as the change of force constant at the surface. Some analytical expressions for force constant calculation are obtained for the first time with this semiempirical models. It is shown that the scheme is fairly simple, yet accurate enough within the frame of tight‐binding theory.
Electronic Structure of SmH2
Authors: Gupta R. Sen , Chatterjee S.
Published: July 2007

The electronic energy bands of SmH2 are calculated using composite wave variational method. The presence of two low‐lying bands below the d‐bands supports the general characteristic of dihydride. Between the two bands, the antibonding band Γ overlaps the metal d states which indicates a depopulation of metal d bands. The electrical and magnetic behaviour of SmH2 is analyzed in the light of this depopulation. A discussion about the formation and stability of SmH2 is made in terms of the relative positions of various energy bands. From the band structure data, density of states, optical properties, and Fermi surfaces are calculated and interpreted.
EPR of a New O Centre in KCl
Authors: Callens R. , Callens F. , Matthys P. , Boesman E.
Published: July 2007

EPR results are given of a new O2− paramagnetic defect, formed following room temperature X‐ray irradiation in KCl, heavily doped in the melt with KNO2. The EPR spectra indicate that the O2− molecular ion has two equivalent equilibrium positions between which it jumps. Above 10 K the EPR spectrum of this molecular ion is orthorhombic, with principal axes [110], [001], and [110]. Below this transition temperature the principal axes are tilted by 1° with respect to the [110] and [110] directions in the (110) plane. A possible model for the perturbing impurity responsible for this tilt is proposed.
Carrier Heating in GaAs by Nonradiative Recombination
Authors: Rühle W. W. , Leo K.
Published: July 2007

Heating and cooling of a photoexcited electron–hole plasma is investigated by time‐resolved luminescence at low lattice temperatures (< 10 K) in Czochralski grown GaAs. Heating processes are experimentally detected by generating (with photon energies close to the band gap) a cool plasma and studying its heating process to temperatures higher than the lattice temperature. The influence of these heating processes on the cooling rate of a hot electron–hole plasma is demonstrated.
Analysis of the Intensity and Polarization Dependence of Two‐Photon Absorption in the Channel E3/2(4f)−E3/2(5d) for Ce3+ in CaF2
Authors: Makhanek A. G. , Korolkov V. S. , Yuguryan L. A.
Published: July 2007

A calculation is made of the parity‐forbidden two‐photon absorption cross section of the transition between the lowest Stark sublevels for a tetragonal site Ce3+ (symmetry C4v) in a cubic fluorite crystal as well as of polarization characteristics of a CaF2:Ce3+ monocrystal with different orientations (k ∥ [100], k ∥ [110], k ∥ [111], k is the wave vector of the incident laser beam). The calculated cross‐sectional value (σ0 = 3.7 × 10−54 cm−4 s) and the polarization dependences agree with experiment.
Magnetic Behavior and Crystal Field of Pr3+ in Praseodymium Selenate Octahydrate
Authors: Nandi J. , Neogy D.
Published: July 2007

Measurements are made on the principal magnetic susceptibilities and anisotropies of praseodymium selenate octahydrate single crystals in the temperature range 90 to 300 K. Although the effective magnetic moment is close to the free ion value, the anisotropy is quite high at room temperature. A least squares fit of the Curie‐Weiss law to the observed average susceptibility yields −36.5 K as the paramagnetic Curie temperature. An analysis of the results with a crystal field (CF) of D4 symmetry, explains the observed results quite well. The CF and the spin‐orbit interaction matrix is block diagonalized in the complete 33 dimensional basis of the 3H term in order to obtain the Stark energies and their eigenstates. Intermediate coupling effects are also considered. The ground state being a singlet, the g‐factors are absent. Some predictions on the electronic heat capacity and the electronic quadrupole splitting are made in the light of the proposed CF.
A Theory of Higher‐Order Correlations. I. Ising Model with Spin \documentclass{article}\pagestyle{empty}\begin{document}$ \frac{1}{2} $\end{document}
Authors: Šamaj L.
Published: July 2007

An analytic method for finding highly accurate values of the transition temperature for the spin \documentclass{article}\pagestyle{empty}\begin{document}$ \frac{1}{2} $\end{document} Ising model is presented. The method is based on the previously introduced formalism, where certain well defined higher‐order correlations are treated by means of physical considerations. In this way, an inadequate description of the higher‐order correlations within the correlation reduction theory is removed. The results for the critical temperature for all cubic lattices are consistent with series expansions to within ≈ 20%.
On the Pinning of Spin‐Density Waves by Impurities
Authors: Seidel Ch.
Published: July 2007

In a nonperturbative way, using the Bosonization technique the behaviour of longitudinal and transverse SDW's in a random field of impurities is studied. It is shown that magnetic as well as nonmagnetic species can pin SDW's. However, the pinning strength of nonmagnetic impurities is found to be essentially reduced compared to the CDW pinning. In contrast to this, locally strong pinning is expected to appear at kinks in the spin‐density phase. Thus, continuously changing the kink density by a magnetic field applied parallel to the easiest axis a significant enhancement of the pinning should be obtained when the period of kink lattice is commensurate with 2kF, i.e., with the period of the superstructure.
Correlation between the Structures of GeS Glasses and that of Impurity Mn2+ Complexes
Authors: Zhilinskaya E. A. , Lazukin V. N. , Bychkov E. A. , Rosenkov S. B.
Published: July 2007

EPR method is used to study the Mn impurity in glass system (GeS)x(GeS2)100−x for 0 ≦ x ≦ 80. Three types of Mn2+ centers homogeneously incorporated in the glass network are found. They have different coordination numbers and different magnitude and symmetry of crystal field. The dependence of the parameters of Mn2+ EPR spectra on glass composition is obtained for every Mn2+ center. The results are compared with known glass structure data.
Lattice Dynamics of B.C.C. Transition Metals
Authors: Mishra S. K. , Singh T. N.
Published: July 2007

A theoretical model for the lattice dynamics of b.c.c. metals is develoed. Contribution to ion‐ion interaction is evaluated applying the valence force field. The contribution to the potential energy from ion‐electron interaction is considered by a screened Coulomb potential. Computed phonon dispersion curves and Debye characteristic temperatures for α‐iron and tungsten on the basis of the model compare well with the experimental results. The Cauchy discrepancy is expressed in terms of an angle‐dependent potential energy in the present model.
Electrical Resistivity Due to Electron–Phonon Scattering in Thin Gadolinum Films
Authors: Urbaniak‐Kucharczyk A.
Published: July 2007

The contribution to the electrical resistivity due to the electron–phonon scattering for the special case of h.c.p. structure is derived. The numerical results obtained for the case of polycrystalline gadolinum films show the resistivity dependence on the film thickness and the surface properties.
Low‐Temperature Electron Transport in Quasi‐Two‐Dimensional Systems
Authors: Pratsch Chr. , Suhrke M.
Published: July 2007

A theoretical approach including multi‐subband coupling is applied to electron transport in quasitwo‐dimensional systems. This results in a modified contribution of the several scattering mechanisms to the total scattering rate. Taking into account the dominant scattering mechanisms the low‐temperature mobility is calculated in the electric quantum limit and is compared with experimental data for heterojunctions and single quantum wells (particularly consisting of Ga1−x. AlxAs/GaAs).
Behaviour and Hysteresis Losses of Irreversible Type‐II Superconducting Cylindrical Shells
Authors: Saif A. G.
Published: July 2007

The internal magnetic field distribution in a type‐II superconducting cylindrical shell is determined. The superheating – and the supercooling – fields are developed. The effect is shown of a transport current on the creation and annihilating of the potential barrier for high χ‐cylindrical shell. The ac losses are studied in the frame of the general critical state theory. For a high‐Tc superconducting sample, smaller superheating – and supercooling – fields than that for conventional superconductors are obtained.
Macroscopic Dynamic Theory of Polar Interface Modes of Superlattices
Authors: Enderlein R.
Published: July 2007

The dynamic theory of polar interface (IF) modes of superlattices is developed. The former electromagnetic theory of these modes is reformulated in terms of sheet polarization charges and currents. The spatial variations of the various electromagnetic field vectors of IF‐modes as electric polarizations, dielectric displacements, and electric field strengths are calculated. Within the dynamic theory polar IF‐modes are characterized by relative mechanical displacement fields having no bulk sources and vortices but sheet sources and vortices on interfaces. A set of Newtons equations is derived for the relative mechanical displacement fields. This set is solved, and the equivalence of the dynamic and electromagnetic approaches with respect to eigenfrequencies is demonstrated. The displacement field eigenvectors are calculated and proven to be orthogonal and complete. They are discussed with the regard of their polarizations and spatial variations. With the exclusion of vanishing wave vector component q parallel to SL‐layers they are neither longitudinal nor transverse but elliptically polarized with polarization ellipses depending on z. For q = 0 the relative mechanical displacement fields of IF‐modes are confined to one of the two SL‐materials, just like for confined bulk modes. The displacement fields are quantized, and the electron–IF‐phonon interaction Hamiltonians are given both for deformation potential and Fröhlich coupling.
Determination of Polariton–Phonon Interaction Parameters in Anthracene Crystals
Authors: Maksimov A. A. , Tartakovskii I. I. , Krivenko T. A.
Published: July 2007

The resonant Raman scattering of light and luminescence excitation spectra of anthracene crystals (T = 1.5 to 40 K) under resonant excitation by a tunable dye laser near the bottom of the lowest exciton band (ωT = 25096 cm−1) are studied. The mean free paths of polaritons for Stokes and anti‐Stokes scattering by optical and acoustic phonons of different branches and values of polariton phonon interaction matrix elements are obtained. The calculated mean free paths for anti‐Stokes scattering by acoustic phonons at T ⪆ 5 K are in a good agreement with the experimental data.
Investigation of the Valence Band Structure of Thermoelectric (Bi1−xSbx)2Te3Single Crystals
Authors: Stordeur M. , Stölzer M. , Sobotta H. , Riede V.
Published: July 2007

Using combined optical‐spectroscopic and transport investigations it is succeeded for the first time to determine all relevant valence band data for the whole series of mixed crystals (Bi1−xSbx)2Te3(0 ≦x≦ 1). The reflectivity of polarized infrared light including its anisotropy is measured in the wave number range of 300 to 4000 cm−‐1. In addition to the spectra the Hall coefficients ϱ123and ϱ312, the electrical conductivity σ ⟂c, and the Seebeck coefficientS⟂care also given. In term of a six‐valley band model and scattering by acoustical phonons all experimental data are consistently described. The main axis massesm, the ellipsoid tilt angle ϑ, the effective density‐of‐states massmd, and the susceptibility massesm,∥care calculated in dependence on composition, also the Fermi levelEF, the carrier densityp, the mobility μ ⟂c, the high frequency dielectric constant ϵ∞⟂,∥c, and the relaxation time τopt. For the first time the structure factors in the Hall coefficients are given. In the plotm(x) the distinct maxima ofmandmdnearx= 0.8 are evident and important for the application of these substances.
Measurements of Ultrafast Optical Nonlinearities in Semiconductors
Authors: Fluegel B. D. , Sokoloff J. P. , Jarka F. , Koch S. W. , Lindberg M. , Peyghambarian N. , Joffre M. , Hulin D. , Migus A. , Antonetti A. , Ell C. , Banyai L. , Haug H.
Published: July 2007

The response of a bulk semiconductor platelet under the influence of nonresonant pulse excitation below the band gap is measured using femtosecond laser techniques. These optical Stark effect measurements are analyzed using the effective Bloch equations for semiconductors. These equations are solved (i) dynamically in the large detuning, low intensity limit and (ii) for arbitrary intensities in the adiabatic limit.
Resonant and Off‐Resonant Light–Matter Interaction in Semiconductors Kinetics and Transients
Authors: Zimmermann R. , Hartmann M.
Published: July 2007

Kinetic problems for off‐resonance excitation (dynamical Stark effect) and resonant excitation (laser‐induced gaps) are studied. Within the Hartree‐Fock theory, Stark shift and bleaching of the exciton line are evaluated. The influence of photon statistics on light‐induced gaps is investigated. Open questions concerning the transient response are clarified.
Evaluation of the Hartree‐Fock Theory of the Excitonic Optical Stark Effect
Authors: Ell C. , Müller J. F. , Sayed K. El , Banyai L. , Haug H.
Published: July 2007

Semiconductor band‐edge absorption spectra of a probe beam under the action of a nonresonant pump beam are evaluated and analyzed, both for two and three dimensional systems. Many‐body effects such as phase space filling and carrier–carrier Coulomb interactions are included within the Hartree‐Fock approximation. In contrast to the atomic optical Stark effect one obtains an exciton blue shift with a nearly constant (2d) or sligthly increasing (3d) exciton oscillator strength. In addition, effects due to the time dependence of the fields are studied, taking pump pulse width, polarization relaxation time and the time delay between pump‐ and probe pulse into account. Deviations from the time independent Hartree‐Fock calculations occur both, with respect to the shift itself and with respect to the shape of the outcoming signal. The results do not reflect all features of earlier experiments, but they are in agreement with recent experimental observations.
Spectral Investigation of the Switching Dynamics in CdS Absorptive Bistable Devices
Authors: Daunois A. , Bigot J.‐Y. , Oberle J. , Eddeqaqi N. Cherkaoui , Wegener M. , Witt A. , Klingshirn C.
Published: July 2007

The transmission spectra of CdS platelets are studied at room temperature with a time‐resolved pump‐probe technique. These measurements are also performed during the switching between the two transmission levels of the bistable crystal induced by the pump pulse. In this case, the third beam from a cw argon laser holds the sample around the switching threshold. These spectral and temporally resolved experiments allow the analysis of the switching dynamics of such absorptive bistable devices.
Optical Bistability and Formation of Localized and Moving High Absorption Domains in ZnSe and ZnCdS
Authors: Esipov S. E. , Stadnik V. A.
Published: July 2007

Results are given of the experimental study of increasing absorption optical bistability that arises from the formation of high absorption domains in bulk ZnSe and ZnCdS. A periodic domain motion causes output signal pulsations. The average domain velocity proved to be about 102 cm/s. A model that describes the behaviour of the absorption domain in semiconductors is discussed. Results of the experimental study of the domain behaviour are explained by the heat conduction regime of the model.
Transverse Effects in Optical Bistability for Transportation of Light Information Signals
Authors: Apanasevich S. P. , Lyakhnovich A. V.
Published: July 2007

The transformation kinetics is studied experimentally of wide light beam profiles at optical switching of the states of bistable thin‐film interferometers with nonlinearity of their thermal nature. The evolution of switch‐wave type autowave processes and inhomogeneous stationary structures at the stages of their stable existence and decay are traced. The possibility is shown of optical control of the direction and speed of switch wave front motion.
Optical Nonlinearities of Semiconductor Microcrystallites
Authors: Woggon U. , Henneberger F. , Müller M.
Published: July 2007

An investigation is made of both, the linear and nonlinear optical properties of semiconductor microcrystallites embedded in glass. The specific situation when the radius of the microcrystallites is 5 to 10 times larger than the bulk exciton radius is studied using CuBr microcrystallites. In this case the observed blue‐shift of the exciton peak is explained in terms of exciton–exciton interaction in the presence of quantum confinement. Effective optical switching at cryo‐ and room temperature is achieved with very large contrast and Lorentzian saturation intensities in the 100 kW/cm2 range. Also the change of transmission with rising excitation intensities of CdS microcrystallites is analyzed with respect to its physical origin. Here a strong broadening due to a large size distribution results in a more complex situation.
Room‐Temperature Optical Nonlinearity in Semiconductor‐Doped Glasses
Authors: Zimin L. G. , Gaponenko S. V. , Lebed V. Yu.
Published: July 2007

The bleaching effect in commercial samples of glasses is investigated at the fundamental absorption edge of semiconductor microcrystals responsible for the colour of the glass. At room temperature under an optical excitation intensity up to 107 W/cm2 an increase of the optical transmission by five orders and more is observed. The spectral band width in which nonlinear optical response occurs reaches 0.5 eV. The results are compared with the results obtained for nonlinear absorption of semiconductor monocrystals.
Carrier Diffusion and Trapping by Quantum Wells
Authors: Uchiki H. , Kobayashi T. , Tokunaga E.
Published: July 2007

A picosecond time‐of‐flight experiment is performed for GaAs/AlGaAs quantum well structures at 77 K in order to obtain diffusion constants and trapping rates of carriers by quantum wells. Analysis of the data by a diffusion model gives an ambipolar diffusion constant of AlxGa1−xAs (x ≈ 0.35) of 16 cm2/s and a capture efficiency of carriers by a single quantum well with 5 nm width of 0.75.
Many‐Body Effects in the Electron–Hole Plasma Confined in GaAs–(GaAl) As Quantum Wells
Authors: Bongiovanni G. , Staehli J. L. , Martin D.
Published: July 2007

Two‐beam transmission and photoluminescence spectra of GaAs–(GaAl)As multiple quantum wells are presented. The spectra are studied as a function of the electron–hole (c–h) pair density. At low and with increasing density a blue‐shift of the lowest exciton line is found. At densities above the Mott value, the band gap reduction depends on the width of the well and is much smaller than in a strictly two‐dimensional e–h plasma. Further, even in a relatively dense plasma the excitonic enhancement factor differs strongly from unity, though it depends only weakly on the energy.
Reflectivity and Dynamic Gratings in Implanted Si Induced by Picosecond Laser Pulses
Authors: Galeckas A. , Netiksis V. , Petrauskas M. , Vaitkus J.
Published: July 2007

The relaxation processes are investigated in high‐excited ion‐implanted silicon using transient‐reflectivity and dynamic grating methods in the picosecond time domain. The dependences of the optical parameters of ion‐implanted Si versus implantation dose are presented. The temporal behaviour of the non‐equilibrium charge carriers obtained from the induced‐reflectivity change and grating decay measurements is analysed. The reflectivity decay process is found to be always faster than the corresponding grating decay process. By the numerical calculations the surface recombination velocity is estimated to S = 4 × 104 cm/s. The influence of the implantation process on the effective carrier lifetime is discussed.