bluuebunny/crossref_metadata_2025_split huggingface dataset:
Field Dependence of Dilute Ising Paramagnets
Authors: Taggart G. B. 
Published: July 2007

AbstractQuenched and annealed dilute, spin one‐half, Ising paramagnets are studied under the influence of an external magnetic field of arbitrary magnitude. Both cases are considered for non‐interacting and interacting magnetic species. The short range magnetic interactions are taken into account by using, to the first order in the interaction strength, the exponential operator technique introduced by Honmura and Kaneyoshi. The results clearly show the differences between the behavior of the magnetization and susceptibility as magnetic interactions are turned on for the quenched and annealed cases. For the annealed dilute paramagnet, the magnetization and concentration are calculated for arbitrary external field and chemical potential and, as expected, exhibit phase behavior similar to a three‐state, spin‐one, Ising model.
Parametric Excitation of Laser in Magnetoactive Doped Piezoelectric Semiconductors
Authors: Aghamkar P. , Sen P. K. 
Published: July 2007

AbstractUsing the hydrodynamic model of a semiconductor plasma, a detailed analytical investigation of parametric excitation is made for a doped piezoelectric semiconductor in presence of a large transverse magnetostatic field. The analysis deals with the qualitative behaviour of the threshold condition and the gain mechanisms with respect to the doping level and the magnetostatic field. Numerical estimates are made for n‐InSb crystals at 77 K duly shined by a 10.6 μm CO2 laser. Efforts are directed towards optimizing the doping level and the applied magnetic field for the occurrence of parametric excitation using the lowest possible threshold to yield the maximum possible gain. The analysis suggests the possibility of observing parametric gain in a moderately doped magnetoactiv n‐InSb crystal even under continuous wave laser irradiation for an excitation intensity as low as 1 W cm−2.
The Relation between the Orientation of Streamer Discharges and Anisotropy of Thermal Vibrations of Atoms in II‐VI Semiconductors
Authors: Zubritskii V. V. , Purlys R. P. 
Published: July 2007

AbstractFor the first time the relationship is established between the thresholds (probabilities) of excitation of streamer discharges and anisotropy of thermal atomic vibrations of crystal lattices in semiconductors. By the example of cadmium sulphide for the first time the temperature dependence of streamer orientation at 294 K is modelled by doping the samples with lithium impurities; the mean‐square dynamic displacements of atoms are measured, and it is shown that the dynamic characteristics of crystal lattices of doped semiconductors cardinally differ from analogous parameters for undoped crystals, but as in purposely undoped samples, their anisotropy determines the temperature dependence of the excitation thresholds of streamers.
The Kinetic Theory of the Orientational Ordering Phase Transition. The Model and the Kinetic Behavior
Authors: Yang Zhengju , Ma Guangquen 
Published: July 2007

AbstractUsing a simple microscopic model, the kinetic equations of the orientational ordering phase transition are established and the general characters of the kinetic behavior of the first‐order and the second‐order phase transitions are obtained. The results about the equilibrium state obtained as a special case agree completely with those obtained from the phenomenological theories of the first‐order and the second‐order phase transitions. The different behavior of these two kinds of phase transitions is explained by a unified model. Meanwhile, the relation between them is given and the possibility of a system transiting from one to another caused by external influence is discussed. Lastly, it is shown that in such a non‐equilibrium process, a “potential function” corresponding to the thermodynamic force can be established which is equivalent to the free energy function in the thermodynamics in the equilibrium state and can be used to give the direction and speed of the phase transition in the whole non‐equilibrium process too.
Self‐Similarity of the Density of States of Electron and Phonon Models in Fibonacci Chains. An Analytic Study
Authors: Böttger H. , Kasner G. 
Published: July 2007

AbstractFor periodic one‐dimensional phonon and tight‐binding electron models, the densities of states are expressed through the trace of the dynamic transfer matrix. The resulting formulae are used for studying the self‐similarity of the spectrum of Fibonacci chains.
Diamagnetic Susceptibility of a Donor in a GaAs/Ga1−xAlxAs Quantum Well Heterostructure and Its Pressure Dependence
Authors: Sukumar B. , Navaneethakrishnan K. 
Published: July 2007

AbstractThe diamagnetic susceptibility (χdin) of a donor in the GaAs quanturn well of the GaAs/Ga1−xAlxAs heterostructure is calculated for a well of infinite strength. The binding energy of the donor electron in different magnetic fields is computed variationally and the χdia values estimated using the Langevin expression. It is found that as the well width increases the χdia values also increase, Using the pressure dependence of the effective mass, dielectric constant, and lattice constant of GaAs, the donor ionization energies are estimated for different pressures of 50 × 108, 150 × 108, and 200 × 108 Pa applied along the growth axis of the superlattice. It is shown that both, the ionization energies and χdia values increase with pressure for a given well width. Also the ionization energy decreases with increasing well width in the presence of both, pressure and magnetic field.
Quantum Oscillations of Galvanomagnetic Effects in Bismuth Bicrystals
Authors: Muntyanu F. M. , Onu M. I. , Kistol V. G. 
Published: July 2007

AbstractThe quantum oscillations of galvanomagnetic effects are studied in bismuth bicrystals with a crystallite boundary of an inclination or twisting type. The quantum oscillations of the Hall components of a the resistivity tensor, that occur due to a quanturn interaction between the charge carriers and intercrystallite boundary are observed. It is shown that the character of the quantum oscillations of galvanomagnetic effects in the Bi bicrystals depends essentially on the tilt angle of the crystallites.
Anisotropy of Magnetoresistance of the p‐Type Ferromagnetic Semiconductor HgCr2Se4
Authors: Kostylev V. A. , Gizhevskii B. A. , Samokhvalov A. A. , Auslender M. I. , Bebenin N. G. 
Published: July 2007

AbstractAn experimental investigation is made of the anisotropy of magnetoresistance of the ferromagnetic p‐type semiconductor HgCr2Se4 on specimens doped with intrinsic defects and Ag. A simple theory is developed dealing with the magnetoresistance of the p‐type ferromagnetic semiconductor with Γ8 symmetry of the valence band top split by a strong exchange field produced by localized spins. The theory provides a good description of the experimental data.
Generation of Picosecond Acoustic Pulses by Laser Radiation in Piezosemiconductors
Authors: Gusev V. E. 
Published: July 2007

AbstractTheoretical description is proposed of the frequency spectrum of strain pulses, excited by optical generation of nonequilibrium charge carriers in piezocrystals. The acoustic pulses are excited by the inverse piezoeffect by electric fields induced by spatial separation of electrons and holes. The conditions necessary for picosecond strain pulse generation are determined. The possibility of acoustic pulse excitation with duration governed by Debye screening time is predicted. It is shown that piezomechanism of optoacoustic transformation may be more effective than thermoelastic and electronic mechanisms.
Coherent Signal Generation in CuCl by Light‐Induced Grating and Induced Biexciton Decay
Authors: Lévy R. , Gomes M. J. M. , Kippelen B. , Hönerlage B. 
Published: July 2007

AbstractUsing a picosecond light source and a streak camera as detection system, the temporal evolution of the signal generated throughout degenerate four‐wave mixing (DFWM) experiments is analysed in CuCl at low temperature. The signal emission shows different temporal behaviour depending on whether the test pulse reaches the surface of the sample before, during, or after the pump pulse. This enables one to distinguish the light‐induced grating contribution from the induced decay of quasi‐particles. The latter process can then be used to determine their dephasing time.
Tellurium Diffusion in the Mixed System CdxHg1−xTe
Authors: Madhavan Y. , Ramachandran K. , Haridasan T. M. 
Published: July 2007

AbstractLattice dynamical calculations on the jump frequencies of different isotopes of tellurium in the mixed system CdxHg1−x Te are worked out following the general theory of diffusion for metals by Achar, assuming an active role for the vacancy. An isotope effect, which is a measure of the diffusion rate is also deduced. The lattice dynamics of this mixed system is worked out in the virtual crystal approximation using the rigid ion model of Plumelle and Vandevyver. The results indicate that diffusion is carried out prominently by the single vacancy mechanism.
Lattice Dynamics of Ca and Sr in B. C. C. and F. C. C. Phases. A dynamic treatment
Authors: Singh N. , Singh S. P. 
Published: July 2007

AbstractThe pair potential defined for transition metals in a previous paper is extended to study the phonon dispersion of alkaline earths. The overlap between d states on different ions and the effect of sd hybridization are included in ion‐ion interaction as has been suggested by Wills and Harrison. The temperature dependence is also included through an asymptotic factor. The calculated dispersion curves do not differ from experimental values by more than 10% for both, Ca and Sr in both, f. c. c. and b. c. c. phases except at a few wave vectors near the zone boundary in the case of Ca(b. c. c). The binding energy and elastic constants are also calculated and compared with existing experimental data.
Vibrational Spectra of CuGaS2 and CuGaSe2 Compounds and CuGaS2xSe2(1−x) Solid Solutions2)
Authors: Bodnar I. V. , Smirnova G. F. , Karoza A. G. , Chernyakova A. P. 
Published: July 2007

AbstractThe phonon modes of the ternary compounds CuGaS2, CuGaSe2, and the CuGaS2xSe2(1−x) solid solution are investigated by means of IR and Raman Spectroscopy. The dependence of the frequences on the composition of the solid solutions is obtained. It is shown that the lattice vibrations of the solid solutions display mixed type behaviour.
A Field‐Theoretical Treatment of Third‐Sound Localization
Authors: Kleinert P. 
Published: July 2007

AbstractThe nonlinear σ model approach to Anderson localization is studied for third‐sound modes of a 4He film on a disordered substrate. The disorder is assumed to be spatially long‐range correlated. Gaussian and exponentially decaying correlations are considered. From the renormalization group equation a nonlinear equation is derived for the renormalized diffusion coefficient. The localization length and numerically calculated diffusion spectra are discussed.
Self‐Energy of an Electron in the Vacuum Gap between Two Metals
Authors: Thoai D. B. Tran , Zeitler E. , Nam Do 
Published: July 2007

AbstractExpressions for the self‐energy of an electron at rest in the vacuum gap between two identical metals are derived using the formalism of Manson and Ritchie. Besides the quantum recoil effects, the effects of the spatial dispersion are included using the hydrodynamic model. The numerial results show that the effects of the spatial dispersion are even stronger than the quantum recoil effects. The corrections to the classical image potential due to the quantum recoil effects play a role only for small gap separation. However, the spatial dispersion increases the range of gap separation, at which the corrections to the classical image potential are non‐negligible.
The Functional Equations for the Kinetic and Exchange Energy Functionals
Authors: Baumann G. , Duscher R. 
Published: July 2007

AbstractThe Hohenberg‐Kohn theorem proves the existence of a universal energy functional. But still its explicit structure is unknown. Unknown parts of the energy functional, namely the kinetic and the exchange interaction energy are discussed. Based on a functional formulation of the virial theorem “functional equations” for these unknown quantities are deduced establishing a relation between the functional and its derivative. Though there is no general formalism for solving such equations they may be used to determine the structure of the unknown functionals. Starting with simple formal assumptions for the exchange energy, some well‐known approximations are derived for this functional thus proving the value of this new technique.
Antisite Defects in SiAlAs/GaAs Modulation‐Doped Superlattices
Authors: Wang En‐Ge , Zhang Li‐Yuan , Wang Huai‐Yu , Jin Wei‐Min 
Published: July 2007

AbstractThe electronic structure and binding energy of the antisite defects GaAs and ASGa in SiAlAs/GaAs modulation‐doped superlattices are calculated with use of the developed recursion technique. A detailed comparison between the antisites and impurities in the multilayer systems is presented based on the discussion of the local density of states and the electronic occupation possibilities on each defect site. The results are used to explain recent experiments.
Theory of the Residual Resistivity Dipole. Flow of Non‐Interacting Particles under a Weak Driving Force around a Fixed Point Scatterer
Authors: Lenk R. 
Published: July 2007

AbstractEmploying a superposition representation of the density matrix the perturbation of the stationary current flow by a fixed point scatterer is treated approximately. The current is driven by a weak constant force. The problem, the method, and the result parallel closely those of the corresponding force‐free diffusion case discussed previously. For all current‐proportional perturbation terms, the Einstein equivalence between a force and a density gradient is established for the inhomogeneous case under study. This equivalences, however, is broken by an additional current‐free term of the density matrix. This term can be identified as a relict of the inhomogeneous equilibrium state in the given static force field. This equilibrium state itself is also studied. In the ensemble the limitations of the concept of a local chemical potential become evident, even in the current‐free state.
Auger Recombination in Heavily Doped Semiconductors
Authors: Quang Doan Nhat 
Published: July 2007

AbstractA theory is developed of the Auger recombination in a heavily doped semiconductor, taking into account the influence of the random inpurity field. For various recombination processes, general analytic expressions of the Auger coefficients are derived, which describe the effect of the random field in explicit dependence on the doping concentration, compensation, and excitation levels as well. The degeneracy and screening effects of non‐equilibrium carriers are shown to be of great importance. It is found that the Auger coefficients may be strongly enhanced due to the impurity field up to several orders of magnitude at high doping concentration and low excitation level. The numerical evaluation on p‐type GaAs indicates especially that in the case of low temperature (77 K) and high acceptor concentration (> 1019 cm−3) the random field effect on the valence band process is predominant over that caused by the phonon. Moreover, in a n‐type material the valence band process is predominant over that caused by the phonon. Moreover, in a n‐type material the valence band process might be competable with the conduction band one even at weak excitation.
Theory of R. F. Mössbauer Spectra of the Magnetics with Magnetic Anisotropy
Authors: Sadykov E. K. , Skvortsov A. I. 
Published: July 2007

AbstractThe theory of the r. f. collapse phenomenon in nuclear γ resonance (NGR) for magnetics is proposed. In contrast to the existing rotating‐field and stepwise‐field models this approach takes into consideration the detailed behaviour of the magnetization (consequently of hyperfine field (HF) under external r. f. field and magnetic anisotropy field. Using the Liouville superopetor technique the expression for NGR absorption cross‐section (57Fe) is obtained on the basis of time periodicity of the HF alone. The possibility of the chaotic evolution of the magnetization in some cases and the corresponding changes in the NGR spectra are shown. Numerical model calculations for a system of single domain particles with uniaxial anisotropy using the chain fraction method are carried out. So the matter under discussion is a quantitative to the r. f. collapse regime valid for an arbitrary time dependence of the HF.
Spin Glass Properties of Zn1−xMnxSe
Authors: Graf A. , Obermaier R. , Gebhardt W. 
Published: July 2007

AbstractFaraday rotation is measured in Zn1−xMnxSe as a function of temperature and magnetic field in the range between 5 and 50 K and fields up to 5 T. Two characteristic temperatures, T1B) and T2B), are observed. T1 can be interpreted as transition temperature into the spin glass state which is supported by a plot of the Edwards‐Anderson order parameter qEA(T). The time dependent magnetization is investigated at T < T1. It is found that the decay of the themoremanent and isothermal remanent magnetization fits well a stretched exponential function.
NQR Measurements of 63Cu in YBa2Cu3O7−x
Authors: Grande S. , Lippold B. , Mayer G. , Schmiedel H. 
Published: July 2007

Abstract63Cu‐NQR measurements are performed in powdered samples of superconducting YBa2Cu3O7−x (YBaCu) in weak external magnetic fields B0 < 2 mT at temperatures T > Tc (normal conducting state). The NQR‐echo amplitudes exhibit damped oscillations with increasing magnetic field B0. The theoretical evaluation of these oscillations allows the direct determination of the asymmetry parameter η of the electrical field gradient (EFG) tensor and the local magnetic field at the Cu‐sites in the lattice of YBaCu.
Stimulated Echo and Vibrational Dynamics
Authors: Hizhnyakov V. 
Published: July 2007

AbstractStimulated echo (SE), excited in an inhomogeneously‐broadened vibronic absorption band of impurity centres by three successive pulses, is considered. SE for a small delay time t2 of the second pulse, comparable with the characteristic time of vibrational relaxation, is essentially determined by the vibrational dynamics of the excited centres. The processes of a absorption and amplification of the third exciting pulse are differently modulated by vibrations, giving different contributions to the amplitude of SE. The absorption contribution is described by the function A(t3, t2, t2), while that of the amplification by A(t2, t3, t3), where A(μ, τ, τ′), is the correlation function of the resonance secondary emission of centres. For very short t2 and t3, i. e. essentially smaller than the periods of vibrations, the latter can play a role of inhomogeneity in the system, allowing one to observe the SE on homogeneous systems, such as ionic crystals with colour centres (F‐centres).
A Model Calculation of the Dielectric Band Structure of Diamond and Silicon
Authors: Castro J. D'Albuquerque E , Muniz R. Bechara , Oliveira L. E. 
Published: July 2007

AbstractA model microscopic dielectric response previously proposed is used to calculate the dielectric band structure of diamond and silicon along several symmetry directions in the Brillouin zone. The most screened dielectric eigenpotentials at the Γ point are also obtained. Comparison of the present results with previous model calculations provides an indication that the model dielectric response used is satisfactorily accurate and realistically incorporates local‐field effects.
Ultrafast Nonlinear Optical Effects in Biased Semiconductor Quantum Wells
Authors: Chemla D. S. , Schmitt‐Rink S. , Knox W. H. , Miller D. A. B. , Goossen K. W. , Hasnain G. 
Published: July 2007

AbstractThe development of electronic and photonic devices operating in the many‐THz regime will require the invention of novel structure concepts and will implement physical processes different from those presently used in optoelectronics. An analysis is reviewed of the physical mechanisms that can be implemented to generate, propagate and detect femtosecond electrical signals in properly designed semiconductor quantum well structures. Also discussed are recent experimental investigations of these effects as well as the fundamental limitations caused by two photon absorption.
Screening of the Coulomb Potential in the Athermal Stage of Highly Excited Direct‐Gap Semiconductors
Authors: Heiner E. 
Published: July 2007

AbstractEquations for the reduced density operator are evaluated. Investigating the subdynamics of nonrelevant observables a resolvent formulation is obtained selfconsistently for the screening part of the evolution superoperator in the athermal nonequilibrium. The analysis is taken in the limit of many collisional events and corresponds to an extension fo the RPA‐result. Thereby, the short memory approximation is improved.
Phonoriton Transient Phenomena
Authors: Gippius N. A. , Ivanov A. L. , Tikhodeev S. G. , Vygovskii S. G. 
Published: July 2007

AbstractThe modifications of exciton optical properties of a direct‐band semiconductor due to anti‐Stokes Raman scattering of intense polariton wave (phonoriton effect) are investigated theoretically. Special attention is paid to the role of ABC and to the reflection of short pulses. A possibility of processing light by means of total internal reflection from pumping beam boundary is proposed.
Kinetics of Partially Coherent Polaritons in Scmiconductors. Schwinger‐Dyson Equations
Authors: Beloussov I. V. , Shvera Yu. M. 
Published: July 2007

AbstractA derivation of the equations is given describing kinetic and dynamic properties of a high density polariton system excited in direct‐gap semiconductors by an external laser field. Keldysh diagram technique for non‐equilibrium processes formulated in terms of functionals is used. Using functional Legendre transformation the Dyson equations are obtained for normal and abnormal connected Keldysh‐Green's functions, which describe quantum fluctuations in the system, as well as for a coherent amplitude of the polariton field. The vertices in the Dyson equations are calculated using perturbation theory.
Self‐Supporting Acoustoelectronic Pulses Driven by Optical Excitation of a Semiconductor in the Transparency Region
Authors: Kochelap V. A. , Kuznetsov A. V. 
Published: July 2007

AbstractIt is shown that the electron‐phonon interaction under certain circumstances can lead to the existence of moving self‐consistent distributions of lattice deformation and carrier density which are supported by an external optical excitation. They are moving towards the source of light with an intensity‐dependent velocity of the order of the sound velocity. The conditions of existence and the stability of such structures are investigated.
Passive and Active Q‐Switching in an AlGaAs/GaAs SQW Laser. Giant Stark Shift in the Laser p‐n SQW Heterostructure
Authors: Aleiner I. L. , Chistyakova L. M. , Kokhanovskii S. I. , Seisyan R. P. , Toropov A. A. , Shubina T. V. 
Published: July 2007

AbstractA giant Stark shift is observed in AlGaAs/GaAs p‐n SQW heterostructures grown by MBE and LPE. The band edge shift determined from the photocurrent and transmission spectra is several times higher then predicted by the quantum confined Stark effect for pure QW in a pin structure. An efficient active Q‐switching is demonstrated in an injection laser with an intracavity monolithic loss modulator.
Possibilities for Intrinsic Optical Bistability in Semiconductor‐Doped Glasses
Authors: Peschel Th. 
Published: July 2007

AbstractEquations of motion for the excitation rate of electron‐hole pairs in semiconductor microcrystals are derived for excitation with picosecond pulses. The inhomogeneous and nonlocal character of the polarization is taken into account. The result are equations describing the macroscopic susceptibility of a semiconductor‐doped glass. On this basis different possibilities for resonatorless optical bistability due to local field effects are discussed and necessary conditions for its appearence are derived.