bluuebunny/crossref_metadata_2025_split huggingface dataset:
The Effect of Long‐Range Disorder on the Optical Spectra of Tetrahedrally Bonded Semiconductors
Authors: Maschke K. , Overhof H. , Thomas P. 
Published: July 2007

AbstractA comparison is made of the configurational averaged spectral function for amorphous ZnS obtained from a pseudopotential (CPSP) and a muffin‐tin (CKKR) approach using the same scattering correlation function. This function leads to a relaxation only of the long‐ range order in the CKKR scheme whereas for the CPSP scheme short‐range potential fluctuations are also introduced. As a result, the CKKR conduction band states are affected equally by disorder. Only the pseudopotential states exhibit selective changes which are essential in order to obtain agreement with experimental spectra. It is, therefore, concluded that short‐range potential fluctuations are responsible for the difference in ϵ2 of amorphous and crystalline semiconductors.
Ground State Energy of the Truncated Anderson Hamiltonian
Authors: Rudra P. 
Published: July 2007

AbstractThe ground state energy of the Anderson Hamiltonian for infinite dd correlation energy is calculated using the method of thermodynamic Green's functions. The quantum mechanical ground state energy has a term proportional to exp (−α · ed/rv2) for rv2 ⪅ 1.5 where ed, r, v denote the energy of the d‐electron, the density of state and strength of interaction between the d‐electron and the conduction band electrons, all expressed in dimensionless units. The value of α remains almost constant over a wide range of the physical parameter rv2.
Recoilless Fraction of Iodine Ion in RbI, NaI, and KI by the Shell Model
Authors: Sneh  , Dayal B. 
Published: July 2007

AbstractRecoilless fraction f(T) of iodine ion in RbI, NaI, and KI has been calculated at different temperatures using the simple shell model. The temperature dependence of the shell model parameters is taken into account by a method discussed by Pandey and Dayal in their study of thermal expansion of ionic crystals. The calculated values of f(T) are compared with available experimental results and good agreement is obtained.
Exciton Polaritons in HgI2 Crystals
Authors: Akopyan I. , Novikov B. , Permogorov S. , Selkin A. , Travnikov V. 
Published: July 2007

AbstractAt low temperatures a detailed study of the emission and reflection spectra of HgI2 crystals in the region of the ground state n = 1(Γ−Γ) exciton resonance has been carried out. It is found that the shape of the resonant exciton emission spectra in allowed and forbidden polarizations E ⊥ cand E ‖, and the relative positions of the emission and reflection spectra are similar to that in many direct gap semiconductors with the high oscillator strength of n = 1 exciton transition. The emission and reflection spectra of the HgI2 crystals are correlated with the energy structure of the exciton resonance using the polariton model. The interrelation between the resonant exciton emission and the exciton absorption is discussed. The polariton dispersion curves in the region of the n =1 exciton resonance in HgI2 crystals are calculated on the basis of experimental data.
Biexcitons in Indirect‐Gap Semiconductors: Applications to GaSe and AgBr
Authors: Quattropani A. , Forney J. J. , Bassani F. 
Published: July 2007

AbstractThe effective mass approximation for biexciton states is extended to semiconductors with indirect gap. An equation similar to that valid for direct‐gap semiconductors is obtained for the envelope function. The electron‐hole exchange contribution is formally the same as that for the direct‐gap case. Intervalley interaction lifts the degeneracy of the biexciton ground state. The procedure is applied to the case of GaSe and AgBr, where the ground state multiplet of the biexcitons is related to the band structures.
On the Connection between Electric and Magnetic Properties of the Hubbard Model I. Electrical Conductivity
Authors: Nolting W. 
Published: July 2007

AbstractAn approximate expression for the electrical conductivity σ is derived by means of the method of spectral moments. Therefore, σ is written in terms of a spectral density, for which a suitable ansatz is chosen. Free parameters of this ansatz are fixed by equating moments. The so obtained approximate solution of the conductivity tensor fulfils the well‐known sum rules and contains nearly all exactly calculable limiting cases. Furthermore, Moneckes statement that the conductivity exhibits free acceleration behaviour even in the case of strong electronic correlations, is shown to be incorrect.
Theory of Electro‐Absorption in Heavily Doped Semiconductors
Authors: Yang E. 
Published: July 2007

AbstractThe imaginary part of the interband dielectric function of a heavily doped semiconductor in the presence of a uniform electric field is calculated. The expression is calculated directly from the Kubo equation in the one‐electron approximation. The average over the impurity coordinates is carried out by means of the cluster integral technique and small time approximation. Under the weak field and low temperature approximation, the dielectric function of a heavily doped semiconductor in the presence of a uniform electric field may be calculated explicitly. It can be expressed in two terms; one is the Franz‐Keldysh effect and the other is due to the impurities in the semiconductors. The results are given for both n‐ and p‐type semiconductors.
The Critical Voltage Effect in Transmission Electron Microscopy IV. Influence of High‐Order Systematic Reflections
Authors: David M. , Gevers R. , Serneels R. 
Published: July 2007

AbstractThe second order critical voltage effect in centrosymmetrical crystals without absorption is discussed in the general linear (2n + 1)‐beam system. It is shown that the qualitative description in the three‐beam approximation remains valid, provided one corrects the value of the critical voltage. A study of the effect in noncentrosymmetrical and absorbing crystals is prepared; it is shown that a three‐beam approximation will be sufficient for these discussions as well.
Jahn‐Teller Effect on the Optical Absorption Spectra of CdS:Ti2+ and CdSe:Ti2+
Authors: Rosenfeld A. , Boyn R. , Ruszczynski G. 
Published: July 2007

AbstractA study is made of electron‐phonon interaction at Ti2+ centres in CdS and CdSe by analyzing the temperature dependence of the 3A2 → 3T1(3F) and 3A2 → 3T1(3P) absorption bands of these systems. Triplet structure in the 3T1(3F) band due to coupling with τ2‐type vibrations is found for CdSe, just as earlier reported for CdS, while the 3T1(3P) bands do not exhibit pronounced structure for both host substances. This behaviour is discussed on the basis of a cluster model involving coupling only to the displacements of the impurity and ligand ions. A point‐charge estimate shows that for both the 3T1(3F) and 3T1(3P) excited states the overall coupling to τ2‐type vibrations should be rather strong. The different shapes of the two bands can be interpreted in such a way that the 3T1(3F) states are especially sensitive to a group of τ2 vibrations having very low frequency, whereas the 3T1(3P) states are mainly coupled to higher frequency τ2 vibrations.
Interface States in a Linear Model of Heterojunctions
Authors: Kandilarov B. D. , Detcheva V. , Petrova P. C. 
Published: July 2007

AbstractThe necessary and sufficient conditions for the existence of interface states in a heterojunction between a one‐atomic and a two‐atomic crystal are derived on the basis of a linear model using the scattering theoretical method of Saxon and Hutner. A discussion of the general features of the above conditions and their interpretation is given and particular cases are visualized applying numerical analysis.
Influence of the Form of the Random‐Field Probability Functional upon the Interband Dielectric Function and Its Modulation by an External Field
Authors: Esser B. , Herzog F.‐N. 
Published: July 2007

AbstractA method is developed enabling one to take account of the influence of an arbitrary random‐field probability functional of a disordered semiconductor on both the interband dielectric function ε(ω) and its external field induced change ε(ω). The influence of a deformation of the Gaussian distribution upon ε(ω) and Δε(ω) is considered. The corresponding plots are presented. The change of the exponential linear tail in Δ2(ω) due to the random Franz‐Keldysh effect is found to be small. The functions Δε1(ω) and Δε2(ω), however, are more sensitive to the particular form of the random‐field probability functional.
A Criterion for Energy Gaps in Three‐Dimensional Disordered Alloys
Authors: Lehmann G. 
Published: July 2007

AbstractA new general criterion for the existence of band gaps in disordered alloys is given. It is represented as a condition for the generalized logarithmic derivatives in the potentials of the alloying constituents at spheres circumscribing the Wigner‐Seitz cells. Other three‐dimensional gap criteria published up to now are contained as special cases. The application of the new criterion is not restricted to approximations for the potentials and to the condition of corresponding states in the systems of pure constituents. A comparison with criteria for one‐dimensional systems is given.
Pseudopotential Method and Thermodynamics of Alloys. II. The Calculation of Intermediate Phases in Alloys with limited Solubility
Authors: Fuks D. L. , Zhorovkov M. F. , Panin V. E. 
Published: July 2007

AbstractTo construct the thermodynamical potential of an ordering alloy the pseudopotential method is applied. The conditions of the intermediate phase formation are studied in systems with limited solubility. Possible reasons for a narrow homogeneity region of these phases are established. An analysis is made of the dependence of phase equilibrium on composition and temperature. Numerical calculations are given for the BaCd system, having a b.c.c. lattice.
The Optical Properties of In2Te3
Authors: Hughes O. H. , Nikolió P. M. , Doran C. J. , Vujatović S. S. 
Published: July 2007

AbstractThe fundamental band gap of In2Te3 as a function of temperature has been deduced from transmission measurements. The absorption edge is due to direct allowed transitions and the room temperature band gap is 1.13 eV. The Debye temperature is found to be 200 °K. Reflectivity measurements in the infrared range indicate the existence of a complex rest‐strahlen band with four peaks in the value of ε2 at 143, 155, 180, and 190 cm−1. The first peak is attributed to a TO lattice phonon mode and the other three to localised modes due to the statistically vacant In sites.
The β Parameter and Velický's Approximation in the Calculation of the Optical Properties of GaAs
Authors: González O. D. Castaño , de Dios Leyva M. , Alvarez R. Pérez 
Published: July 2007

AbstractThe optical properties of GaAs are calculated by the Kramers‐Kronig dispersion relation s A study is made of the method proposed by Velický, establishing a rigorous bound which permits to neglect an infinite number of terms in the series which gives the contribution of. the unknown part of the spectrum for the phase angle. A possible interpretation of the extrapolation parameter β is proposed. Also, the causes of the inadmissible values obtained for the extinction coefficient are made a bit clearer. Values for the interband transition energies in the range 0 to 25.3 eV, for the plasma frequency, and plasmon lifetime are reported.
Structural Phase Transitions in BaMF4 Antiferromagnets
Authors: Dvořák V. 
Published: July 2007

AbstractTwo‐dimensional antiferromagnets BaMF4 where M = Mn, Fe, Co, or Ni exhibit a linear magnetoelectric effect. It is known that this effect is forbidden by symmetry unless a structural phase transition takes place in these compounds. Recently such phase transition was discovered in BaMnF4. Using the group theory and the knowledge of magnetic structure and magnetoelectric effect, essential characteristics of this structural phase transition, i.e., symmetry of the phase transition parameter, possible symmetry changes, anomalous dielectric and elastic constants, are determined.
s–d Interaction in the Transition Range between Metals and Insulators: CdS: Mn
Authors: Spehlich G. , Múller H. 
Published: July 2007

AbstractIn metallic compounds with low charge‐carrier concentrations the Korringa relaxation rate can be so small that it reaches the order of magnitude of the direct spin–lattice relaxation rate. We report on an ESR investigation of CdS doped with the S‐state ions Mn and Eu, where between both contributions to the homogeneous ESR line‐width could be distinguished. Mn‐doped CdS turns out to have an extremely small Korringa slope of the ESR linewidth. We were able to vary this slope from zero to about 0.02 G/K by variation of the electric conductivity of CdS from insulator to a compound with metallic behavior.
Electric Field Gradients in Hexagonal Crystals of Cd, Zn, Gd, and Te Acting on Sm, W, and Os Impurities
Authors: Roesch L. Ph. , Kulessa R. , Horber F. 
Published: July 2007

AbstractThe quadrupole interactions of the 2 + states of Sm, W, and Os isotopes have been studied by using time‐integrated perturbed angular correlations. It has been possible to derive the electric field gradients by applying known data of the quadrupole moments of the implanted probe nuclei. A comparison with the calculated ionic contribution of the lattice shows that great importance has to be attributed to the conduction electrons.
Jahn‐Teller Effect in the Ligand Field Theory of Trigonal Bipyramidal V4+ Complexes
Authors: Bhattacharyya B. D. 
Published: July 2007

AbstractA ligand field model for 3d1 ions with approximate D3h site symmetry has been developed which satisfactorily explains the fine structure parameters, the EPR spectra, and the magnetic susceptibility. The treatment includes the essential features of Jahn‐Teller distortion and covalency effects which are found to have important bearing on the nature of the Jahn‐Teller distortion. Finally by the spin Hamiltonian formalism of Pryce the g‐values and magnetic susceptibility arecalculated. Attempts are made to fit the experimental data of optical absorption, gr‐values, and magnetic susceptibility with a set of parameter values in the theoretical expressions at different temperatures. From this an estimate is made of covalency and Jahn‐Teller parameters.
On the Calculation of Mode Grüneisen Parameters in Rubidium Halides
Authors: Kress W. , Jex H. 
Published: July 2007

AbstractRecently both authors have calculated the mode Grüneisen parameters of RbI using different methods. A critical comparison is made and the consequences of different approximations for the third order coupling constants are discussed. It is shown that the pressure dependence of at least five shell model parameters has to be taken into account in order to reproduce the measured pressure derivatives of the elastic and dielectric constants. In the most stringent approximation, however, where only the third order terms of the rigid part of the shell model are taken into account in the central potential approximation, qualitative agreement with the measured mode Grüneisen dispersion curves is still maintained.
The Parasusceptibility of Gadolinium
Authors: Hof H.‐j. , Kronmüller H. , Rothfuss B. 
Published: July 2007

AbstractThe parasusceptibility, 𝔵p, of Gd single crystals was measured in the temperature range between 4.2 and 290 K, and in the field range from 0.07to 3.0 T. Below 0.8 Tc the parasusceptibility depends linearly on temperature and the field dependence follows a H‐0.44. law. The experimental results are interpreted by means of the spin wave theory taking into account the indirect exchange coupling, the dipolar interactions, and the anisotropy of the energy spectrum of the conduction electrons.
Experimental Evidence of an Electronic Localization in n‐Type InSb Using a Microwave Technique
Authors: Ferre D. , Dubois H. , Biskupski G. 
Published: July 2007

AbstractIt is well known that, when irradiated by two microwaves of frequenciesv1 and v2, a sample of n‐type indium antimonide generates a beat at the intermediate frequency (i.f.) v [v1 _ v2]; that superheterodyne‐detecting property originates from the non‐linearity ofthe I‐U characteristic in weak electric field. It is shown here that, if the classical results about InSb bolometer mixer are valid whenelectrons are free, a new feature appears when localized and delocalized electronic states are both present in the crystal; in this case, the signal detected at i.f. frequency must be separated into two parts: the beat generated by free electrons at frequency v on the one hand and the “response” of localized electrons subjected to this beat on the other hand. It is also shown that information obtained about electronic localization is in good agreement with that one previously deduced from resistivity measurements. In conclusion, such a method appears to be a very convenient way of sonding electronic distribution in a given material.
Structure and Effective Interionic Potential of Liquid Titanium
Authors: Waseua Y. , Tamake S. 
Published: July 2007

AbstractX‐ray diffraction patterns from liquid titanium have been obtained at 1700 and 1850 °C. After calculating the interference function in Fourier analysis, the atomic radial distribution function is obtained from which interatomic distance and coordination number are estimated. Comparingthe results with the structure of liquid calcium, a broadening of the firstpeak maximum is found in the pair distribution function of liquid titanium. The Born‐Green equation is analyzed numerically to derive the effective interionic potentials from the observed structural data. The temperature insensitive long‐range oscillatory potentials are found.
On the Connection between Electric and Magnetic Properties of the Hubbard Model II. Optical Absorption
Authors: Nolting W. 
Published: July 2007

AbstractThe optical absorption, caused by interband transitions between quasiparticle bands, is investigated within the limits of the Hubbard model for a system of correlated electrons in a narrow energy band. Thereby first of all the influence of magnetic orderings over absorption spectra is discussed. It is shown that a phase transition paramagnetism ↔ ferro‐magnetism is signalled by a significant modification of the absorption curves. The numerical evaluation is done for a simple cubic lattice for arbitrary band occupation n and arbitrary interaction constant I.
Image of a Stacking Fault
Authors: Indenbom V. L. , Sh. Slobodetskii I. 
Published: July 2007

AbstractThe wave field of X‐rays is investigated in a crystal with a stacking fault whose line of intersection with the scattering plane is parallel to the surface. The conditions are regarded in which the stacking fault acts as a diffraction lense focusing the X‐rays. The solutions found are illustrated by calculated semi‐shadow maps of the images of stacking fault and intensity distribution of the wave field in the scattering plane of the crystal.
Anderson's Hamiltonian for an Electron in a Distorted Crystal Lattice
Authors: Mezincescu G. A. 
Published: July 2007

AbstractThe matrix elements of the Hamiltonian of an electron in a randomly distorted crystal lattice are estimated for a complete and orthonormal system of localized functions, related to the Wannier functions. The estimates agree with the usual neglection of the stochastic behaviour of the off‐diagonal matrix elements. A numerical calculation for the conduction band of Na is in good agreement with the estimated values of the matrix elements.
Luminescence from the Excited States of Excitons in CdS and CdSe Single Crystals
Authors: Vlasov G. K. , Brodin M. S. , Kritskii A. V. 
Published: July 2007

AbstractThe photoluminescence in “pure” crystals of CdS and CdSe atT  1.4, 4.2, and 77 °K and high exciton concentration has been investigated. The correlation between arising (having mainly threshold character) of luminescence from the excited states of excitons A(n  2, 3) and B(n  1) and the existence of a fine structure, related to radiative recombination due to inelastic collisions between excitons (P, P2, P3, P4, and PB−lines) is observed. It is shown that with increasing excitation the “blue” shift of P‐line is twice than that for the A(n  1)‐line. The analysis of the problem using kinetic equations leads to conclusions about the possibility of stimulated enlargement (similarly to laser generation) of exciton concentration in their excited states due to Auger‐throwing of the excitons into these states at luminescence of P‐lines. The numerical estimations correspond to the experimental condition and the agreeement to the theory with experiment permitsto conclude that the observable luminescence from the excited states is dueto the stimulated generation of excitons in these states.
Galvanomagnetic properties of anisotropic semiconductors of the p‐Te type
Authors: Tomchuk P. M. , Shenderovskii V. A. , Gorley P. N. , Gavaleshko N. P. , Solonchuk L. S. 
Published: July 2007

AbstractExpressions for the independent galvanomagnetic resistance tensor components in weak magnetic fields are obtained for p‐Te type semiconductors, using a variational method. Carrier scattering by optical lattice vibrations is considered without using the relaxation time approximation. With p‐Te as an example, the temperature dependence of the tensor components is studied both theoretically and experimentally for temperatures between 77 and 300°K. From comparison between the calculated and measured values of components, the constants for carrier interaction with polar optical phonons are estimated.
Influence of the electron–electron scattering on the kinetic effects in many‐valley semiconductors
Authors: Mitin V. V. , Tolpygo E. I. 
Published: July 2007

AbstractThe conductivity and magnetoresistance (MR) of a many‐valley semiconductor are calculated for the case when electron scattering on impurities and on the electrons of the same and of the other valleys is characterized by different coupling constants. It is shown that, with increasing anisotropy of the ellipsoidal energy surfaces, the contribution of the electron–electron scattering grows rapidly and MR decreases. The ratio of the coupling constants may be determined unambiguously through analysing the stress dependence of the conductivity and of MR in these semiconductors. The piezomagnetoresistance is shown to increase along with growing electron–electron scattering.
Theory of impurity excitation transfer via a phonon field
Authors: Godenko L. P. , Mashkevich V. S. , Shadchin E. A. 
Published: July 2007

AbstractProcesses of impurity excitation energy transfer are studied by the method of quantum correlation functions. The probabilities of the process are calculated. The probability dependence on the spacing of the interacting centres is determined. The contribution of the process to the guest centre spectral line width is investigated.
Near‐edge spontaneous photoluminescence in GaSe1–xSx
Authors: Kuroda N. , Nishina Y. 
Published: July 2007

AbstractPhotoluminescence spectra of GaSe1–xSx (0 ≦ x ≦ 0.2) are investigated at 4.2 K by the time resolving method. The shift in the photon energies of the luminescence lines with respect to the chemical composition x may be understood without any quantitative contradiction if one employs the empirical model that the direct conduction band edge lies 5 meV below the indirect one, whereas the ground state of the direct exciton lies 13 meV above that of the indirect one in ϵ, γ‐GaSe at 4.2 K. The direct–indirect gap reversal occurs near x = 1 × 10−2.
Ab‐initio pseudopotential calculation of static and dynamic crystal properties of H.C.P. metals
Authors: Hafner J. , Eschrig H. 
Published: July 2007

AbstractHarrison's ab‐initio pseudo‐potential scheme is applied to Be and Mg. The influence of the core–valence and the valence‐valence electron exchange and correlation on the atomic radius, the binding energy, the bulk modulus and its pressure derivative, the equation of state, and the phonon spectra is investigated. Satisfactory agreement with experiment is reached.