bluuebunny/crossref_metadata_2025_split huggingface dataset:
Photoluminescence of a Dense Quasi‐2D Electron‐Hole System in a Modulation‐Doped Heterostructure with Strained InGaAs QW
Authors: Butov L. V. , Kulakovskii V. D. , Andersson T. G. 
Published: July 2007

AbstractThe photoluminescence of dense homogeneous quasi‐2D electron‐hole (e‐h) system in the strained InGaAs QW is investigated for the modulation‐doped n‐AlGaAs‐InGaAs‐GaAs heterostructure under excitation density up to 105 W/cm2 and magnetic field H ≦ 8.3 T. The many body effects are found to become well pronounced in the emission spectra when the concentration of the photoexcited e‐h pairs exceeds the electronic density due to modulation doping (1012 cm−3). There are found and investigated i) the band gap renormalization, ii) the effective mass renormalization, and iii) the change of the damping of one‐particle states in the dense e‐h system.
Multistability of Absorption Domains in Bulk CdS Due to Band Edge Nonlinearities
Authors: Stadnik V. A. 
Published: July 2007

AbstractThe domain instability phenomenon in semiconductors of CdS are investigated. Multistability of high absorption states is explained by features of the nonlinear behaviour of the absorption coefficient and the longitudinal transport of photoexcitations. It is shown that for the explanation of the observed effects besides the thermal mechanism of the nonlinearity the process of the saturation of the excitonic absorption should be taken into account.
Quantum Confined DC Stark Effect in Microcrystallites
Authors: Rossmann H. , Schülzgen A. , Henneberger F. , Müller M. 
Published: July 2007

AbstractThis paper reports on the electric field induced absorption change in the situation of zero‐dimensional quantum confinement. We have studied CdS microcrystallites embedded in glass by a sensitive modulation spectroscopy technique at room temperature. We observe a two‐line spectrum and a quadratic dependence on the applied field. This absorption change is related to the Stark shift of the lowest electron‐hole pair state of the quantum dot.
Excitonic Optical Nonlinearity in II‐VI MOCVD‐Grown Crystals
Authors: Zimin L. G. , Gaponenko S. V. , Malinovskii I. E. , Lebed V. Yu. , Kuznetsov P. I. , Yakushcheva G. G. , Kuznetsov A. V. 
Published: July 2007

AbstractUsing the method of single‐ and two‐beam laser spectroscopy, the nonlinear optical properties of high‐quality MOCVD‐grown ZnSe and CdSe samples are studied. At nitrogen temperatures the dominating mechanism of absorption nonlinearity is the plasma screening of excitons. Along with this, in the nonlinear response of ZnSe crystals the exciton‐exciton interaction causing band broadening takes place. At room temperatures, in CdSe a strong dependence is revealed of absorption spectrum deformation on the exciting radiation quanta energy which is associated with slowing down of electron‐hole plasma cooling.
The Concept of Production Bias and Its Possible Role in Defect Accumulation under Cascade Damage Conditions
Authors: Woo C. H. , Singh B. N. 
Published: July 2007

AbstractIn the study of microstructural evolution and macroscopic property changes due to radiation damage, the point defects are usually modelled as being produced continuously in time and uniformly in space. Furthermore, the excess of vacancies required to sustain the void growth is assumed to arise entirely due to the preferential trapping of interstitial atoms at dislocations. It is shown that this approach may not be appropriate for cascade damage conditions where both vacancies and interstitials are produced in a highly localized and segregated fashion. A model is presented which takes into account the effects of both, vacancy and interstitial clustering in the cascade zones on the defect accumulation rate (e. g. swelling rate) under cascade damage conditions. The consideration of interstitial clustering in the cascade yields a production bias which is found to be a potent driving force for void swelling in addition to the one provided by the dislocation bias.
Adsorption of H2O (Molecular and Dissociative) on Si(100) and Si(111) Surfaces Considered by an Empirical Pair Potential Method
Authors: Engler C. 
Published: July 2007

AbstractThe adsorption of H2O on Si(100) and Si(111) surfaces is examined by an empirical method, which connects pair potential considerations with the BEBO‐concept. For both surfaces, only small energetic differences between molecular SiH2O and dissociative SiH and SiOH species are obtained, which lie within the margin of error of the method. For the dissociation process of adsorbed H2O‐molecules on Si(100)−(2 × 1), the course of the total energy along a possible reaction path is discussed.
Scattering of Two‐Dimensional Electron Gas on the Semibounded Three‐Dimensional Electron Gas
Authors: Boiko I. I. , Sirenko Yu. M. 
Published: July 2007

AbstractFrom first principles, basing on the averaging of the equation for exact fluctuating distribution functions, the classical kinetic equation is derived for a two‐dimensional electron gas (2DEG), interacting with a random potential of an external system. Using the approximation of a Fermi function with a shifted argument for the 2DEG distribution function the frequencies of energy and momentum relaxation are obtained. In the case of equilibrium external system the frequencies are expressed in terms of the dielectric functions of the 2DEG and external system. Energy and momentum relaxation frequencies of 2DEG, scattered on the three‐dimensional electron gas, are calculated.
Positron Band Structures of GaAs and CdTe
Authors: Aourag H. , Khelifa B. , Belaidi A. , Tadjer A. , Rezki M. , Gamoudi M. 
Published: July 2007

AbstractThe problem of positron band structure in aperiodic lattice is similar to its electron counterpart. GaAs and CdTe positron band structures are calculated a comparison between the electron and positron energies is discussed.
Calculation of Local‐Field Correction in the Two‐Dimensional Electron Gas
Authors: Tanatar B. 
Published: July 2007

AbstractThe frequency independent local‐field correction factor G(k) is calculated for the two‐dimensional electron gas. The method is based on decoupling and solving the equations of motion for the charge‐density operator by a moment‐conserving scheme. The expression obtained for G(k) is evaluated by a Monte Carlo integration. The results for G(k) and the static dielectric function ε(k) are tabulated.
Foundations of the Quasi‐One‐Dimensional Bisoliton Model of Superconductivity of Ceramic Oxides
Authors: Davydov A. S. 
Published: July 2007

AbstractIt is shown that in the plane square lattice the most stable self‐localized states are of quasi‐one‐dimensional character. This may serve to substantiate the applicability of a quasi‐one‐dimensional bisoliton model of high‐temperature superconductors containing square plane layers of alternating copper and oxygen ions.
On Mössbauer Spectrum Analysis for Spin Orientation in Fe2As
Authors: Kulshreshtha S. K. 
Published: July 2007

AbstractThe reports of the analysis of 57Fe Mössbauer spectra of Fe2As and the derived spin orientation are inconsistent. To understand the reasons for this inconsistency, the spectra are recorded at various temperatures between 4.2 and 375 K and least squares fitted by solving the complete nuclear hyperfine Hamiltonian matrix using different sets of fitting parameters. The trade off in the fitting of the spectra corresponding to the two iron sites is responsible for this inconsistency. The incorporation of magnetically induced asymmetry parameter in the fitting procedure as suggested in a recent study, did not produce consistent results at all temperatures. The possible reasons for the reported discrepancies are discussed.
A Study of the Disorder in Heavily Doped Ba1–xLaxF2+x by Raman Scattering
Authors: Kolesík M. , Tunega D. , Sobolev B. P. 
Published: July 2007

AbstractThe Raman spectra of the Ba1–xLaxF2+x solid solutions (0.005 ≦ x ≦ 0.31) are presented. The low‐frequency scattering is studied in some detail. The spectra indicate that no large clusters are present in solid solutions studied. A cross‐over which can be interpreted in terms of the fracton model is observed.
Modification of the INDO Calculation Scheme and Parametrization for Ionic Crystals
Authors: Stefanovich E. , Shidlovskaya E. , Shluger A. , Zakharov M. 
Published: July 2007

AbstractA new parametrization of the semiempirical quantum‐chemical INDO method is proposed for the study of the electronic structure of a wide class of perfect and defective ionic insulating crystals. The applicability of the “cut‐off function” concept for the calculations of exchange interactions in the large unit cell (LUC) model is also briefly discussed. Both, the proposed calculation scheme and the parametrization are tested on a number of molecules, ionic crystals (LiH, LiF, LiCl, KCl, MgO, K2SO4), and (100) crystal surfaces of LiF, KCl, MgO.
Point Defects in Electron‐Irradiated Stoichiometric Magnetite
Authors: Walz F. , Kronmüller H. 
Published: July 2007

AbstractHigh‐purity, stoichiometric, single crystalline magnetite (Fe3O4) has been electron (e−)‐irradiated below 45 K to a dose of 1023 electrons/m2. Radiation‐induced point defects give rise to both drastic modifications of intrinsic electronic processes and the occurrence of reorientation‐type magnetic relaxations. Both phenomena offer deeper insights into the mechanisms of (i) electronic charge transport and (ii) thermally activated reactions of interstitials and vacancies. Coordination between migration of elementary defects and corresponding anncaling stages can be established in Fe3O4 with higher precision than in any other magnetic system investigated so far.
Computer Simulation on the Threefold Coordinated Oxygen Atom in Vitreous Silicon Dioxide
Authors: Dianov E. M. , Egibyan A. V. , Akopyan S. A. , Rustamyan A. É. , Sokolov V. O. , Sulimov V. B. 
Published: July 2007

AbstractDissociation of SiO bonds in vitreous silicon dioxide is proved to yield threefold coordinated oxygen atoms with three silicon atoms or one oxygen and two silicon atoms being the nearest neighbours. Electronic spectra, wave functions, and transition probabilities are investigated for three charge states of both the defects by the semiempirical LCAO MO method MINDO/3 in a cluster approach.
Strength and Stability of Silver
Authors: Singh G. 
Published: July 2007

AbstractSemiquantitative calculations are made of the theoretical strength and range of stability of a perfect uniaxially stressed crystal of silver by using a pseudopotential. The rigorously estimated total binding energy of the metal consists of kinetic, exchange, and correlation parts along with ion‐ion and electron‐ion interactions. The computed value of tensile strength is 1.01 × 109 N/m2 with a corresponding strain of 2.72%. These values are fairly close to 1.7 × 109 N/m2 tensile strength and about 3% strain observed experimentally for silver whiskers.
On the Effect of Three‐Body Interactions and Proximity of the Fermi Level to the Brillouin Zone Faces on Elastic Modules of Simple Metals
Authors: Fomichev S. V. , Katsnelson M. I. , Koreshkov V. G. , Trefilov A. V. 
Published: July 2007

AbstractA discussion is made in the model of the local pseudo‐potential V(q) ≡ Vq on effects going beyond the scope of the second‐order terms of the Vq perturbation theory for describing the static properties of simple metals. It is shown that the allowance for third order in Vq hardly improves the description of static properties (energy, pressure, elastic modules, etc.), being nevertheless apparently essential for Ba and Al. The effect of non‐sphericity of the Fermi surface ignored in the third order in Vq is discussed in the two‐wave approximation. The ranges of parameters in which the simple perturbation theory in Vq is not adequate are found for the b.c.c., f.c.c., and h.c.p. structures of simple metals alloys in the rigid‐band approximation.
Reflectivity and Photoreflectivity in Superlattices and Quantum Wells
Authors: Ivchenko E. L. , Kochereshko V. P. , Uraltsev I. N. , Yakovlev D. R. 
Published: July 2007

AbstractOblique‐incidence reflectance and photoreflectance of heterostructures near the resonance frequencies of excitons confined in a single quantum well are studied. Under illumination with above barrier band gap light at low temperature, the relative change ΔR/R of the reflectivity is found to reach 10% and even more. The experimental results can be explained by a photo‐induced decrease in the exciton damping and attributed to neutralization of the barrier impurity centres under the illumination.
Experimental and Theoretical Study of Heavy Ion Irradiation Processes in Polymer Materials
Authors: Danziger M. , Andrassy G. 
Published: July 2007

AbstractDue to the fact that the anomalous behaviour of most different physical characteristics in vitreous solids compared with crystalline solids can be described by the action of a system of additional low‐energy excitations, the application of this model to processes in polymer films irradiated with heavy ions, is studied. The irradiated polymer films were etched with simultaneous electrical conductivity measurements. It is shown that the dependence of the radial etching rate on the distance from the trajectory of the heavy ion up to a determined radius can be described by the response function developed from the model of low‐energy excitations.
The Effect of Quantum Screening on the Energy Loss Rates of Hot Electrons in n‐Hg0.8Cd0.2Te in the Extreme Quantum Limit at Low Temperatures
Authors: Bhowmik S. , Sarkar C. K. , Santra K. 
Published: July 2007

AbstractA theoretical model is proposed to calculate the energy loss rates of hot electrons in semiconductors in high magnetic fields at low temperatures. The energy loss due to the acoustic phonon scattering via deformation potential and piezoelectric coupling is considered for lowest Landau level occupancy, i.e. the extreme quantum limit. The model includes the effect of the modified free carrier screening due to Landau quantisation, on the acoustic phonon scattering, assumed to be the dominant loss mechanisms. The band nonparabolicity, the non‐equipartition of acoustic phonons, and the Landau level broadening due to electron‐impurity interactions are also included. The model is used to interpret the experimental results obtained from the specific heat measurements in n‐Hg0.8Cd0.2Te at 1.5 K. The theoretical values of the energy loss rate are found to be larger compared to the experimental values. The inclusion of quantum effects on the free carrier screening overestimates the theoretical energy loss rates.
Impact Ionization of Free and Bound Excitons by Free Carriers in an Electric Field in CdS. Investigation by Optical Methods
Authors: Jakobson M. A. , Kagan V. D. , Katilius R. , Müller G. O. 
Published: July 2007

AbstractQuenching of the exciton luminescence of cadmium sulfide at 1.8 K in a static electric field is observed and attributed to impact ionization of free excitons and delocalization of bound excitons by hot electrons. A continuous transition from the T ownsend‐Shockley to the Davydov‐Wolf law is observed when the field is increased to 1 kV/cm. A theoretical analysis of the results on the quenching of luminescence lines of bound excitons makes it possible to identify the mechanisms of relaxation of high‐energy electrons dominating in CdS at low temperatures. It turned out that these electrons lose their quasi‐momentum by spontaneous emission of piezo‐phonons in “pure” samples and are scattered by impurities in “less pure” samples. The mean free path of 4 meV electrons in moderate fields is 10−4 cm in the “pure” samples and 5 × 10−6 cm in the remaining samples.
Synchrotron Radiation, Radiative Losses, and Polarization Effects for Relativistic Beams in Bent Crystal
Authors: Arutyunov V. A. , Kudryashov N. A. , Mishin O. A. , Samsonov V. M. , Strikhanov M. N. , Sytsko Yu. A. 
Published: July 2007

AbstractExpressions for the intensity of specific radiation accompanying the deflection of high‐energy particles by a bent crystal are presented. It is shown that when R → ∞ (R is the bending radius) the corresponding formulas are transformed into those for channeling radiation in an unbent (straight) crystal. Dipole, synchrotron‐like radiation, and polarization effects are analysed. Numerical calculations of the radiation and polarization in the bent planes using a realistic potential are made for beams with different parameters.
The Size‐Quantized States of the Wannier‐Mott Exciton in Structures with Superthin Films of CdTe
Authors: Pokatilov E. P. , Beril S. I. , Fomin V. M. , Kalinovskii V. V. 
Published: July 2007

AbstractThe results of experimental investigations of excitonic spectra of the CdTe superthin films on MgFe2 are theoretically discussed. The significance of different terms in the experimentally measured quantity — the energy of a photon which generates an exciton — is analysed. The theory is in good quantitative and qualitative agreement with experiments.
A Model Theory of Structural and Superconducting Phase Transitions in Chain‐Like Systems
Authors: Kiselev A. A. , Liaptsev A. V. 
Published: July 2007

AbstractA model Hamiltonian for the study of non‐adiabatic effects caused by orbital degeneracy of electronic states in conducting systems is obtainded basing on the dynamics of a quasi‐one‐dimensional chain of tri‐atomic linear molecules, each in the ground electronic ∏‐state. The Renner‐type electron‐phonon interaction which arises in such systems, differs essentially from Fröhlich's one: it is non‐diagonal with respect to the electronic quantum numbers and quadratic in the phonon operators. This interaction is shown to induce structural and superconducting phase transitions, the structural one lowers the symmetry of the charge density and cause the enlarging of the gap in the electronic spectrum. An example of the Renner‐type interaction in the high‐Tc superconductor is given.
Systematization of Binary Intermetallic Compounds
Authors: Walzer U. 
Published: July 2007

AbstractNorm‐conserving pseudopotentials derived from the Dirac equation serve for the derivation of new characteristic quantities. For each chemical element and each electron shell, two characteristic energy and two characteristic spacing quantities are calculated. Therefrom, functions are formed for binary compounds and alloys of type AB. If two each of these functions are plotted in pairs, an arrangement is obtained according to regions with crystals of the same structure type and same space group, of the same melting temperature class etc. This systematics enables one to eliminate unfavourable combinations in the search for specific physical properties. A few results are plotted.
A Green's Function Estimation of Lattice Relaxation for Isovalent Substitutional Defects in Alkali Halide Crystals over the Entire Composition Range
Authors: Roy (Paul) S. Datta , Sengupta S. 
Published: July 2007

AbstractA Green's function calculation is presented for dilute concentration isovalent substitutional defects in alkali halides. A simple model is suggested to extend this calculation to the high concentration range. Comparing the values of lattice relaxation obtained from this estimation to EXAFS measurement, a very good agreement is noticed over the entire composition range.
Anisotropic Diffusion of Point Defects to Spheroidal Cavities
Authors: Grande N. Smetniansky‐De , Tomé C. N. , Passianot R. 
Published: July 2007

AbstractThe problem of point defects diffusing anisotropically towards spheroidal sinks is solved using an analytical treatment. Depending on the ratios between the sink semi‐axes (a0, b0) and the diffusivity main components (D⟂, Dz), two different situations are solved separately: the prolate and the oblate cases. For each case two boundary conditions are considered: a) periodic sink distribution and b) a constant boundary concentration condition. The results of this study allow to derive qualitative conclusions with respect to the influence of the diffusion anisotropy, the boundary conditions, and the cavity shape on the point defect concentration profiles around spheroidal sinks. In a coming paper these results are applied to study the diffusion of irradiation produced point defects towards cavities and to calculate defect bias and cavity sink strength.
EPR Parameters and Spectral Fine Structure of Ni2+ in LiNbO3
Authors: Zhou Kang‐Wei , Zhao Sang‐Bo , Wu Ping‐Feng , Xie Jun‐Kai 
Published: July 2007

AbstractBy means of the eigenvalues and eigenvectors of the complete energy matrix of the C (d8) ion and the spin Hamiltonian theory, the Spectral fine structure, the EPR parameters (D, g) and the ground state Zeeman splitting of Ni2+ in LiNbO3 are calculated in a unified scheme for the first time. The results agree well with the findings, thus the optical and paramagnetic properties of LiNbO3:Ni2+ are uniformly explained. The theoretical methods, including the g formulae, are suitable for any C (d8,2) ion.
Nonlinear Oscillations and Chaos in CdS Single Crystals under Temperature‐Electric Instability Conditions
Authors: Golik L. L. , Gutman M. M. , Pakseev V. E. 
Published: July 2007

AbstractLow‐frequency chaotic and complex regular oscillations of photocurrent and temperature in CdS single crystals occurring at constant applied voltage and illumination are investigated. Routes from periodicity to chaos are studied. Explanation of the complex behaviour is presented on base of a rate‐equation model of temperature‐electric instability in semiconductors with two types of electron trap levels. Numerical results of computer calculations of the model are in agreement with the experimental results.
On Functional Integral Representations Satisfying the Constraints in the Correlation Models of High‐Temperature Superconductors
Authors: Weller W. 
Published: July 2007

AbstractFunctional integral representations are constructed for Fermions with spin 1/2, in which the fields satisfy directly by construction the constraints (e.g., exclusion of double occupancy of a site) appearing in recent models in the theory of high‐temperature superconductivity. Thus, the enforcement of the constraints by delta functions in the integration measure is avoided. Perelomov's concept of generalized coherent states is used. However, in constructing such representations, exponential functions of linear combinations of operators (which are difficult to disentangle) are avoided, as is the construction and reduction of the invariant measure. Instead, an ansatz is used for the resolution of the unity operator. This approach also provides more freedom in choosing the appropriate fields. Several new and simple representations with only few elementary fields are given. The representation already used by Wiegmann is recovered. In this case and in any other cases the integration measure is explicitly given. In all these representations, the original Fermi operators are substituted by the product of a spin independent Graßmann field and a spin dependent bosonic (complex) field in accordance with the physical idea of separation of charge and spin degrees of freedom. It is further shown how a change in the integration measure eliminates also zero occupancy (the case of the Heisenberg antiferromagnet). The absence of an explicit delta function constraint in the functional integral is reflected in a special form of the kinetic part of the action. The considered representations are compared with that of the slave boson method.