bluuebunny/crossref_metadata_2025 huggingface dataset:
Coherent and conventional quantum 1/f effect
Authors: Handel Peter H.
Published: July 2007

The quantum 1/f theory is the application of a new type of infrared radiative corrections to the calculation of the rate or cross section of elementary physical processes. These new quantum‐electrodynamical corrections, first introduced in 1975, are time‐dependent and represent fluctuations also known as quantum 1/f noise. They define the new notions of physical cross sections and process rates which contain both the fundamental macroscopic low‐frequency quantum 1/f fluctuations and the well‐known, related, classical, and quantum‐mechanical concepts which are constant in time. A simple universal formula allows the calculation of this quantum 1/f effect for any elementary process, such as scattering, recombination, or tunneling in semiconductors, in other condensed matter, or in free space. This yields quantum 1/f fluctuations in the frequency of collisions, in the mobility of the carriers, their diffusion constant and surface or bulk recombination rate. The quantum 1/f effect presented in this paper thus has a fundamental nature and a practical importance because it limits the performance of semiconductor devices and of most other high‐technology applications.
Investigation of the electronic structure of cubic MoxTi1−xCy carbide alloys
Authors: Krainik V. V. , Lisenko A. A. , Ivashchenko V. I. , Bekenev V. L.
Published: July 2007

The electronic structure of MoxTi1−xCy carbide alloys is calculated by means of the APW‐LCAO‐CPA method. On the basis of the electronic spectra a study both of the generalized susceptibility function and of the topology of the Fermi surface is carried out. It is found that stable MoxTi1−xCy cubic carbide alloys can be formed only at sufficiently great amount of Ti atoms (x ≦ 0.2). Stabilization of cubic MoC can be also achieved by replacing a small amount of Mo atoms by Ti atoms together with the formation of carbon vacancies.
Two‐particle energy spectrum in dense electron–hole plasmas
Authors: Arndt S. , Kraeft W. D. , Seidel J.
Published: July 2007

Two‐particle (exciton) states in equilibrium electron–hole plasmas of highly excited semiconductors are determined. In the framework of the Green's function technique, an effective (two‐particle) wave equation allows to account for the influence of the surrounding plasma in terms of (dynamic) single‐particle self‐energies, Pauli blocking factors, and a dynamic effective potential correction. This equation is solved by expansion of the wave function in terms of Coulomb eigenfunctions. No rational or pole approximation for the dielectric function is used. Exciton binding energies and their imaginary parts (damping of the states) as well as continuum edges are given for Ge and GaAs model systems.
Electrical dislocation resistivity and anisotropic scattering in high‐purity copper single crystals
Authors: Sachslehner F.
Published: July 2007

The experimental dislocation resistivity (or the deviation from Matthiessen's rule (DMR)) at 4.2 and 77 K of several single slip and multislip crystals was investigated. Additionally low‐field Hall effect measurements at 4.2K using a dc SQUID picovoltmeter were performed in order to study the anisotropy of electron–dislocation and electron‐impurity scattering directly. It is shown that oxygen annealing applied to increase the “electrical purity” of the crystals does not change the character of the scattering behaviour. The anisotropy parameters Adis for electron–dislocation scattering derived within the two‐group model are in good agreement with recent results for high‐purity polycrystals.
Autosolitons in electron–hole plasma of InSb heated by electric pulses
Authors: Kamilov I. K. , Stepurenko A. A.
Published: July 2007

It is shown experimentally that autosolitons may be excited in indium antimonide by pulses of a strong electric field either in the form of current layers or electric field strata. Several oscillation modes are found in the external circuit of the sample, generated by the solitons moving in the electric field. Each mode is characterized by its own voltage range. Two main mode types are found. For the first type, the frequency of oscillations decreases and the amplitude increases as voltage increases, while for the other, the frequency increases gradually and there is a maximum in the amplitude curve.
Pairing instabilities induced by residual statistical interactions
Authors: Kolley E. , Kolley W.
Published: July 2007

At two space dimensions we consider small changes in quantum statistics around the bosonic and fermionic limits. An anyon gas near the Bose statistics becomes unstable towards pair condensation at arbitrarily small statistical parameter in front of the Aharonov‐Bohm interaction. The self‐consistency problem within the Cooper scattering channel is solved analytically by taking into account the full momentum dependence of the singular two‐particle vertex. The pairing, whose amplitude and critical temperature we calculate in mean‐field approximation, has d‐wave symmetry unlike the p‐wave BCS‐type pairing instability for anyons near the Fermi point. The connection to paired‐boson (holon) superconductivity is pointed out.
Emergence and inflection angles in the configurational dependence of interface bilayer spin wave energies
Authors: Puszkarski H. , Józefowicz R. , Kolodziejczak B. , Akjouj A. , Djafari‐Rouhani B. , Dobrzynski L.
Published: July 2007

For the two interface cubic cuts b.c.c. (110) and f.c.c. (111) we consider the existence regions of interface spin waves (ISWs) in a ferromagnetic bilayer film on the two‐dimensional Brillouin zone (BZ) concerning their size and shape versus the respective interface related parameters (interface exchange coupling and intrinsic interface anisotropy), applying the approximation of a very thick bilayer film and the method of Brillouin zone mapping (BZM). We emphasize the effect exerted on the BZM by varying (in the plane perpendicular to the film) the configuration angle ϑ of the film magnetization with respect to the film normal. We predict the existence of (at most two) critical angles ϑE at which the ISWs emerge. The emergence angles are functions of the in‐plane wave vector k∥ of ISW propagation along the interface. We show that the ISW energy varies monotonously with variations of the angle ϑ attaining zero slope on the edges of the interval of ϑ variability (implying simultaneously the existence of a characteristic point of inflection inside the interval). We prove that the nature of the monotonicity is determined unequivocally by the type of the intrinsic interface anisotropy, namely: the ISW energy grows (decreases) monotonously with the angle ϑ if the interface anisotropy is of easy‐plane (easy‐axis) type. Moreover, we discuss the effects due to the presence of critical and inflection angles with a view to their exploitation in experimental measurements.
Neutron reflectivity of perfect crystals excited by high‐frequency ultrasound
Authors: Iolin E. M. , Rusevich L. L. , Vrana M. , Mikula P. , Lukáş P.
Published: July 2007

Neutron scattering double‐crystal experiments were realized using high‐frequency ultrasonic excitation in a perfect silicon single crystal. The dependence of rocking curves on the ultrasonic amplitude was measured and compared with the dynamical theory. It was found that the method of the transfer matrix is very useful for the analysis of the influence of the acoustic wave (AW) on the diffraction in very thick crystals. In particular, the pendellösung oscillations are simply and exactly removed from the whole picture of the diffraction pattern. Some exact theoretical conclusions concerning the maximum influence of ultrasound and the deformation at the peak intensity in a double‐crystal spectrometer were also reviewed.
Quantum chemical calculations of the electron center diffusion in MgO crystals
Authors: Popov A. I. , Kotomin E. A. , Kuklja M. M.
Published: July 2007

Large‐scale quantum chemical simulations of the diffusion hops of empty cation and anion vacancies, as well as F+and F centers in MgO crystals have been done. The atomic configurations for 224‐site cluster and charge density distribution are analyzed for the equilibrium and saddle‐point configurations during the defect hops. The relevant activation energy for diffusion increases monotonically in the series Va→ F+→ F center.
Average square atomic displacement: A comparison of the Monte‐Carlo and Green's function results
Authors: Shukla R. C. , Boseglav F. , Whybra J. C.
Published: July 2007

Highly accurate results for the mean‐square displacement (MSD) of an atom for a nearest‐neighbor Lennard‐Jones model of a f.c.c. solid are presented. These results are obtained from the Monte‐Carlo (MC) method and the Green's function method. The dependence of MSD on the sample size (N) in the MC method and similarly the dependence of MSD on the number of wave vectors used in the calculation by the Green's function method is discussed in detail. The results are presented by both methods for the infinite sample size limit as well as for the finite sizes, i.e., 32‐, 108‐, and 256‐atom sample sizes and the same number of corresponding wave vectors. It is shown that an analytical method like the Green's function method reproduces almost exactly the results of the MC method (a completely numerical procedure) for all temperatures except at the melting point (Tm). The computing time required in the former method is only a fraction of the latter one.
The temperature dependence of the LO(T) and TO(T) phonons in GaAs and InP
Authors: Irmer G. , Wenzel M. , Monecke J.
Published: July 2007

The LO and TO phonon frequencies and dampings have been measured by near‐infrared Raman spectroscopy both in bulk GaAs and InP. The phonon damping of the LO phonon in InP is much smaller than the LO phonon damping in GaAs. The experimentally obtained temperature dependences were compared with a theory including cubic anharmonic processes and the thermal expansion of the lattice. It is shown that the phonon damping is mainly affected by decay processes into acoustic phonons.
Effects of heat treatment on crystal structure and magnetic properties of LaFe12−xAlxMn compounds
Authors: Guo Yongquan , Liang Jingkui , Tang Weihua , Zhao Yanming , Rao Guanghui
Published: July 2007

The LaFe12−xAlxMn (x = 2, 3, 4, 5, 6, 7) alloys have been annealed at different temperatures and for different periods. The crystal structures and magnetic properties of these compounds are investigated by X‐ray diffraction and ac susceptibility measurements. The results indicate that the NaZn13‐type structure is slightly sensitive to Mn‐doping. However, the magnetic properties of these compounds are strongly related to the annealing temperature and period. A structural transition occurs in LaFe5Al7Mn after annealing at 773 K for about three months. A magnetic transition from ferromagnetic to paramagnetic state is found in LaFe7Al5Mn after annealing at 773 K for two months.
Fluctuations in ferroelectrics and dielectric properties from the Fokker‐Planck equation
Authors: Kaupuzs J.
Published: July 2007

The Fokker‐Planck equation is used to study the dielectric susceptibility dispersion in ferroelectrics within the Landau‐Ginzburg model. Subsequent consideration of fluctuations, recently used for calculations in the paraelectric phase, is extended. The results of a more comprehensive study including calculations for both the ferroelectric phase and refined calculations for the ferroelectric phase are presented here. The obtained results allow to explain qualitatively the resonance dispersion close to the critical point, observed in SbSI‐type ferroelectric crystals. Besides, the diffuse phase transition in relaxor ferroelectrics and its spontaneous transfer to the first‐order phase transition is explained within the considered model.
A search for resonant states from deep levels in GaAs and AlGaAs: Evidence from hall effect studies under pressure
Authors: Saxena A. K. , Singh P.
Published: July 2007

Hall effect studies have been made on LPE grown n‐type GaAlAs (0 ≤ × ≤ 0.78) as a function of pressure and temperature. It has been shown that a resonant state lies 0.205 eV above the Γ edge in GaAs and becomes degenerate with it at × = 0.29. For × ≥ 0.29, the same state appears in the band gap as a deep level. The resonant state has a pressure coefficient of (1.0 ± 0.2) meV/108 Pa which gradually changes sign at × ≈ 0.5 and has a value of −1.5 meV/108 Pa for × ≥ 0.78. A deep level emerges in GaAs under pressure which has properties similar to the DX level in GaAlAs. A reduction in mobility has also been observed due to resonant scattering. A shallow state strongly coupled to Γ also exists in the alloy. The results suggest that the origin of the DX level is an intrinsic crystal defect (other than As vacancy) possibly coupled with an inadvertant substitutional Si impurity.
Multiband conduction in Pb1−xYbxTe
Authors: Mahoukou F. , Santos O. Dos , Fau C. , Charar S. , Averous M. , Golacki Z.
Published: July 2007

Low and high field transport measurements have been performed on polycrystalline Pb1−xYbxTe obtained by the Bridgman technique. Unannealed samples show semi‐insulating conduction at low temperatures while annealed samples remain conducting in the whole temperature range. The results can be explained qualitatively by impurity levels lying within the fundamental gap. Using the magnetic field‐dependent Hall technique, the concentration and mobility of carriers in different bands (or sub‐bands) were extracted showing the coexistence of electrons and holes. The attribution of discrete carriers to each band is discussed.
The spin‐3/2 blume‐capel model on a honeycomb lattice
Authors: Peliti L. , Saber M.
Published: July 2007

The temperature dependences of the magnetization m = 〈〈S〉〉r and of the moments q = 〈〈S2〉〉r and r =〈〈S3〉〉r in the spin‐3/2 Blume‐Capel model on a honeycomb lattice are examined in detail, within the framework of an effective field theory based on the use of a probability distribution that correctly accounts for the single site kinematic relations. A number of characteristic behaviours for their thermal variations are obtained, especially for negative values of the crystal field. Its phase diagram is obtained; besides a second‐order transition line occurring at high temperatures, the phase diagram exhibits a first‐order transition line separating the phases (3/2, 3/2) and (1/2, 1/2).
Neutron scattering study of the phase transition in 1,3 cyclohexanedione crystals at ambient and high pressures
Authors: Bobrowicz L. , Katrusiak A. , Nawrocik W. , Wasicki J. , Natkaniec I.
Published: July 2007

The temperature and pressure dependences of elastic coherent and inelastic incoherent neutron scattering spectra in polycrystalline 1,3‐cyclohexanedione undergoing a first‐order phase transition at 287 K, have been measured. The information on the crystal lattice parameters and thegeneralized phonon density function G(E) is analyzed. The presence of the transition hysteresis and the isomorphous phase transition have been confirmed.
Longitudinal‐Optical‐Phonon effects on excitons in GaAs‐Ga1−xAlxAs quantum well
Authors: Moukhliss S. , Fliyou M. , Sayouri S.
Published: July 2007

We have calculated the effects of the longitudinal optical phonons on the exciton binding energy in a quantum well, consisting of a single slab of GaAs sandwiched between two semi‐infinite slabs of Ga1−xAlxAs, as a function of the size of the GaAs well. We have found that the correction due to the bulk‐like LO‐phonon effects on the exciton binding energy is quite larger than that due to the confined LO‐phonon effects and that these effects on the binding energy of the light‐hole exciton are larger than those of the heavy‐hole exciton. Our results are compared with recent experimental data, and good agreement has been found.
Empirical n‐body potential for cubic metals
Authors: Dimitrov V. I.
Published: July 2007

Many‐body empirical model potentials are formulated in the frameof the embedded‐atom method (EAM) of Daw and Baskes for homonuclear cubic metals. The basic functions of the model (the pair interaction potential electron density function, and embedding energy function) are presentedin analytical forms which do not impose limitations at least on the basic properties of the system like Cauchy discrepancy, equal anisotropy ratio imposed by the Johnson's EAM potential, etc. The developed potentials areconvenient for computer simulations.
The spontaneous magnetization of metallic hydrogen and the Electron‐Phonon interaction
Authors: Yang Qiubo , Zhang Xiangdong , Wu Jianhua , Li Bozang
Published: July 2007

Based on the spin‐polarization theory of ferromagnetism of Hirsch and taking the electron‐phonon interaction into account, we study the effect of electron‐phonon interaction on the spontaneous magnetization ms of metallic hydrogen at zero temperature. It is shown that the lattice vibration not only reduces ms, but also narrows the area of ms ≠ 0.
Bose commutation rule approximation in the theory of spin systems and elementary excitation spectrum
Authors: Derzhko O. V. , Ph. Moina A.
Published: July 2007

The Bose commutation rule approximation for spin operators has been examined using as a testing ground the 1D s = 1/2 generalized XY model. The conditions under which the dependence of the elementary excitation energy on quasi‐momentum is not changed after such an approximationhave been found.
A study of amorphous PdCuSi by internal friction and DSC measurements
Authors: Shui Jiapeng , Chen Xiumei , Wang Can
Published: July 2007

The internal friction of amorphous Pd77.5Cu6.0Si16.5 (a‐PdCuSi) was measured with a conventional torsion pendulum (Ke torsion pendulum) at increasing temperature, and it was found that there are two internal friction peaks (P1 and P2) near the glasstransition temperature Tg and the crystallization temperature Tx of a‐PdCuSi, respectively. From DSC measurements it was found that the origin of the peak P2 is directly related to crystallization, while the peak P1 may be a relaxing internal friction peak. The sensitivity of the inverted torsion pendulum and the Collette pendulum was discussed. We found that the controversy on the measured results of internal friction on a‐PdCuSi is due to the lower sensitivity of thesetwo pendulums.
Electrooptical constants in spherical quantum dots
Authors: Casado E. , Trallero‐giner C.
Published: July 2007

The electrooptical properties of a spherical quantum dot (QD) are theoretically investigated when the QD radius R is smaller than the bulk exciton Bohr radius. The electronic energy levels are obtained as a function of one universal parameter t = 2 [q]m*FR3/h2, where m* and q are the quasiparticle mass and charge, respectively, and F is the applied electric field. The carrier polarization and the interband electron‐hole oscillator strength are investigated as functions of both t and the electron‐hole mass ratio. Using the Kramers‐Kronig relations the change of the complex dielectric constant due to the electric field is derived. A definition of the complex electrooptical function, which describes the main features of the spherical QD optical constants in presence of an electric field, is given. In the strong electric field regime, where perturbation theorycannot be applied to the Schrödinger equation, a quasi‐linear dependence on F is predicted for the electroabsorption variation spectrum. The obtained results are used to explain recent experimental data forthe decay of electron‐hole pairs.
Magnetic properties and band structure of ordered Co2−xNixTiSn compounds
Authors: Jezierski A.
Published: July 2007

The band structure and magnetic properties of the ordered Co2−xNixTiSn Heusler‐type alloys for x = 0, 1, and 2, are studied by using the spin‐polarised TB LMTO method. We found that the Ni2TiSn system is paramagnetic. The self‐consistent band calculations for the systems with vacancy (□) have shown that Co2−x □xTiSn is ferromagnetic but for Ni2−x□xTiSn we did not observe any magnetic moment.
Phonon‐drag effects on thermoelectric power in linear and nonlinear transport conditions
Authors: Wu M. W. , Sun W. , Horing N. J. M. , Cui H. L.
Published: July 2007

We carry out a calculation of the phonon‐drag contribution Sg to the thermoelectric power of bulk semiconductors and quantum well structures for the first time using the balance equation transport theory extended to weakly nonuniform systems. Introducing temperature‐, wavevector‐, and modedependent phonon relaxation times due to phonon‐phonon interactions, the formula obtained can be used not only at low temperatures where the phonon mean free path is determined by boundary scattering, but also at high temperatures. Our analysis of the role of the phonon relaxation times in regard to dependencies on temperature, wavevector, and mode provides results for the linear thermoelectric power Sg which are in agreement with experimental data over a broad range of densities and temperatures. The role of hot‐electron effects in Sg isdiscussed. The importance of the contribution of Sg to the thermoelectric power in the hot‐electron transport condition is emphasized.
Ladder ising spin configurations. I. Heat capacity
Authors: Mejdani R. , Lambros A.
Published: July 2007

We consider a ladder Ising spin model (with two coupled Ising spin chains), characterized by two couplings (interchain and intrachain couplings), to study in detail, in an analytical way, its thermal behaviour and particularly the variation of the specific heat versus temperature, the ratio of interaction constants, and the magnetic field. It is interesting that when the competition between interchain and intrachain interactions is strong thespecific heat exhibits a double peak and when the competition is not so strong the specific heat has a single peak. Further, without entering into details, we give, in a numerical way, some similar results for more complicated ladder configurations (with more than two linear Ising chains). The spin \documentclass{article}\pagestyle{empty}\begin{document}$\documentclass{article}\pagestyle{empty}\begin{document}$ \- \frac{1}{2} $\end{document}$\end{document} ladders or systems of spin chains may be realized in nature by vanadyl pyrophosphate ((VO)2P2O7) or similar materials. All these intermediate systems are today important to gain further insight into the physics of one‐dimensional spin chains and two‐dimensional high‐Tc spin systems, both of which have shown interesting and unusual magnetic and superconducting properties. It is plausible that experimental and theoretical studies of ladders may lead to other interesting physical phenomena.
Local structure in Zn1−xMnxS: EXAFS study
Authors: Łażewski J. , Zimnal‐Starnawska M. , Kisiel A. , Boschbrini F. , Pascarelli S. , Giriat W.
Published: July 2007

The extended X‐ray absorption fine structure (EXAFS) has been measured on the K edge of sulphur in Zn1−xMnxS solid solutions for various manganese contents (0 ± x ± 0.4). Using the wellknown procedure of data reduction, we observed a weak linear increase of anion‐cation and anionanion distances for Mn concentrations changing from x = 0 to 0.4. On the basis of the simulation, using theoretical phases and amplitudes calculated by McKale, the possibility of peak separation in the Fourier transform both in the first and second shells has been discussed.
A study of a fast ionic conductor AgI‐CsI
Authors: Nalini B. , Selvasekarapandian S. , Janaki K.
Published: July 2007

One molar ratio of the compound AgI‐CsI has been taken for the ionic conductivity study. The activation energy has been obtained from the Arrhenius plot. The theory of Rice and Roth has been applied to calculate the number of potentially mobile ions of the conducting species.
Diffusion model of dechanneling based on the Boltzmann equation: Three regimes of energetic particle motion in crystals
Authors: Kashlev Yu. A. , Sadykov N. M.
Published: July 2007

The generalized local Boltzmann equation is derived for the distribution function of energetic particles interacting with the thermal vibrations of the lattice. On using the Boltzman collision term the particle energy losses A(ϵ⊥) and the diffusion function B(ϵ⊥) are obtained. The functions A(ϵ⊥) and B(ϵ⊥) have singularities (fracture, peak) connected with the difference of the contributions of the particles moving in the regimes of channeling, quasichanneling, and random motion.
Photoconductivity and optical absorption of dimorphite thin films
Authors: Tsiulyanu D. , Golban G. , Kolomeyko E. , Melnic O.
Published: July 2007

Optical absorption and photoconductivity of As4S3 thin films have been studied. The absorption coefficient is shown to be influenced by the technology of film preparation, in particular by growth velocity and substrate temperature. An absorption band with maximum at hv ≈ 1.9 eV has been observed at the absorption edge for films prepared at low growth velocities. Simultaneously a maximum appears in the spectral distribution of photoconductivity, the position and width of which also depend on the technology of film preparation. The results are explained with taking into consideration the inhomogeneity of films containing α and β dimorphites revealed by X‐ray diffraction studies.
Electronic states in B δ‐doped Si quantum well
Authors: Gaggero‐Sager L. M. , Pérez‐Alvarez R.
Published: July 2007

This work presents a self‐consistent calculation of the electronic structure of B δ‐doped Si quantum well. By examining the dependence of the energy levels, the Fermi level and the depth of the well with the impurity concentration, it is shown that the model is valid for impurity concentration not higher than 1 × 1014 cm−2 and that the Fermi level is very close to the valence band. Calculations are compared with experimental data obtained for p2D = 2.4 × 1013 cm−2, 3.5 × 1013 cm−2, and 9.5 × 1013 cm−2. The results agree quite well with the experimental results available for this system.
Diluted Ising spin‐1/2 lattice with an arbitrary coordination number
Authors: Cong Bach Thanh , Amraoui Y. El
Published: July 2007

A useful representation for the Callen identity in the case of spin‐1/2 is introduced by a simple technique. The phase diagrams and percolation problems of the diluted Ising lattice with arbitrary coordination number z are also discussed.
Structure and optical properties of lithium niobium‐phosphate glasses and glass ceramics
Authors: De Araujo E. B. , De Paiva J. A. C. , De Araujo M. A. B. , Sombra A. S. B.
Published: July 2007

Lithium niobium‐phosphate glasses [(x Nb2O5(0.5−x) P2O5) 0.5 Li2O]: y Fe2O3 were studied using 57Fe Mössbauer and infrared spectroscopy. The use of both techniques gives new information about the structure and crystalline phases in the pure glassy and glass ceramic systems. The iron atoms are present as Fe3+ and Fe2+ ions and in both cases proved to be surrounded by six oxygen atoms (network modifier). The results suggest that the Nb ions occupy sites of average octahedral symmetry. Precipitation of crystalline phases of LiNbO3 and Li3PO4 was detected.
Optical absorption study of colour centres in SrLaAIO4 single crystals
Authors: Ubizskii S. B. , Savytskii D. I. , Matkovskii A. O. , Gloubokov A. , Pajaczkowska A.
Published: July 2007

The peculiarities of absorption spectra of SrLaAIO4 single crystals are investigated as well as the influence of thermal annealing in air and y‐irradiation (60Co source) on them. A more complex structure of absorption bands was revealed, in contrast to previous investigations. The investigation of changes of absorption spectra induced by annealing and irradiation suggests that both reversible and irreversible processes take place in either case and the oxygen defects are most probably responsible for the observed effects.
Far‐infrared spectroscopy of Hg1−xMnxS alloys
Authors: Popovic Z. V. , Tomic N. , Milutinovic A.
Published: July 2007

The far‐infrared reflectivity spectra of Hg1−xMnxS (x = 0.02, 0.05, 0.10, 0.20, 0.25, and 0.33) alloys were measured in the 30 to 500 cm−1 spectral range at different temperatures and analyzed using a numerical fitting procedure based on the plasmon‐phonon interaction model. The three active modes at about 125, 189, and 305 cm−1 are clearly observed. These modes were assigned as twophonon resonant mode, zone center phonon mode, and disorder‐activated mode, respectively. It was shown that phonons in Hg1−xMnxS alloys (for Mn concentrations x ≤ 0.33) exhibit one‐mode behavior.
Acousto‐helicon interaction in narrow‐gap semiconductors
Authors: Ghosh K. K. , Paul S. N.
Published: July 2007

A theoretical investigation is made on the propagation of acousto‐helicon waves through plasmas in narrow‐gap semiconducting piezoelectric crystals. Interaction coupling of the acousto‐helicon mode sets up at lower frequencies in the small‐gap semiconductors as compared to that in wide‐gap ones. This is because of the strong dependence of the electron effective mass on the nonparabolicity of the conduction band of the semiconductors. Results are also shown for wide‐gap semiconductors for the sake of comparison.
Effect of random local crystal fields on the magnetic properties of rare‐earth RNi5−xCux compounds
Authors: Kuchin A. G. , Ermolenko A. S. , Khrabrov V. I. , Makarova G. M.
Published: July 2007

It was experimentally revealed that the concentration variations of the spontaneous magnetization, Curie temperature, and initial susceptibility of RNi5−xCux alloys (R = Pr, Nd, Tb, Er, Y) were different for various R. The obtained results are qualitatively explained in terms of effects of random local crystal fields appearing in the substitutional alloys.
Method of calculating the critical temperature of three‐dimensional Ising‐like system using the non‐gaussian distribution
Authors: Kozlovskii M. P. , Pylyuk I. V. , Usatenko Z. E.
Published: July 2007

A method for calculating the phase transition temperature Tc based on the theoretical description of the critical behaviour of the model system on the microscopic level is proposed. The main idea of such a calculation is on based a systematic consideration of the influence of the short‐ and longwavelength fluctuations of the spin density on the value of the phase transition temperature. The equation for Tc is obtained as a result of the analysis of recursion relations for the coefficients of Landau‐Ginzburg‐Wilson‐type “effective forms” and consideration of their singular properties in the critical region. As the interaction potential we use an exponentially decreasing function with effective range b. The equation for the critical temperature is obtained and the value of Tc is calculated. The dependence of Tc on the ratio b/c (c is the lattice constant) is investigated. We obtain the value βcJ = 0.211 in the case when the Ising model is approximated by the quartic measure density (ϱ4 model) and for nearest‐neighbours interaction with the interaction constant J.
On the random transverse field mixed spin Ising model of spin‐1/2 and spin‐1
Authors: Weng X. M. , Li Z. Y.
Published: July 2007

The critical behavior of mixed spin Ising model is investigated when the transverse fields are randomly distributed. The calculation shows that when the transverse fields are both bimodally distributed, the transition temperature decreases with increasing transverse field and eventually vanishes at a finite field. When one of the transverse fields is bimodally and the other trimodally distributed, the temperature decreases but does not vanish. When both transverse fields are trimodally distributed, the transverse field dependence of temperature breaks off and a tricritical point appears due to the interaction between quantum fluctuations and disorder.
Scintillation quenching in cerium‐doped ytterbium‐based crystals
Authors: Korzhik M. V. , Drobyshev G. Yu. , Kondratiev D. M. , Borisevich A. E. , Pavlenko V. B. , Timochenko T. N.
Published: July 2007

Luminescence and scintillation in cerium‐activated oxide crystals with complex structure are quenched by co‐doping with ytterbium. It was determined that Ce3+ luminescence is quenched by tunneling ionization and scintillations are suppressed in addition by the destruction of relaxing excited host matrix states by Yb3+ ions and nonradiative transitions Ce3+ → (Yb3+)−.
Mean field behaviour of Sr1−xCaxTiO3
Authors: Chaves M. R. , Almeida A. , Maglione M. , Ribeiro J. L.
Published: July 2007

A systematic analysis of the dielectric constant as a function of temperature in SrTiO3: Ca crystals with Ca content of 0.0020, 0.0032, 0.0055, 0.0058, and 0.0110 shows that the Barrett parameters are clearly modified by the Ca content. We have found for each Ca concentration the temperature below which the contribution of the Ca induced clusters becomes sizeable. The values obtained for the fitted parameters in the Barrett formula allow us to trace a boundary between the low‐temperature quantum paraelectric and ferroelectric regimes.
Stable states in ferroelectric liquid crystals
Authors: Pitanga P. , Mundim K. C. , Filho A. Ribeiro
Published: July 2007

We study the stability of the molecular structure of DOBAMBC

1‐n‐DecylOxyBenzylidene‐p‐Amino‐2‐MethylButyCinnamate.

, a prototype of ferroelectric liquid crystals, using the linear stability analysis for Hamiltonian systems. We show the existence of thermodynamically stable states in a narrow temperature region ΔT = 1 °C, between the A‐phase and the ordinary smectic C*‐phase.
Pressure Dependence of the Electron Effective Mass in GaAs up to the 1s(Γ)‐1s(X) Crossover
Authors: Jiang Z. X. , Chen R. J. , Tischler J. G. , Weinstein B. A. , McCombe B. D.
Published: July 2007

The effect of hydrostatic pressure (P) on the k = 0 conduction band mass m(P) in lightly Si‐doped GaAs is studied by far‐infrared magnetospectroscopy. The electron cyclotron resonance (CR) at (T = 17 K), and the 1s‐2p+ absorption of Si donors (at T = 4.2 K), are measured up to 40 kbar under fields of 6 to 9 T by Fourier transform and laser magnetotransmission techniques. DX‐center trapping is avoided by visible illumination. A double‐bellows diamond‐anvil cell and 36 mm bore magnet enable in situ P‐B‐T tuning. The slopes dE/dB for the CR and 1s‐2p+ peaks decrease with pressure in accordance with effective mass theory, with no sign of strong deepening for the Si 1s(Γ) state. We find m(P)/m(0) = 1 + (6.1 ± 0.3) × 10−3P – (1.3 ± 0.5) × 10−5P2 (P in kbar) from the CR data, after correcting for nonparabolicity via an effective two‐band k.p model. This agrees well with prior results limited to 17 kbar, and extends the measurement of m(P) in GaAs to the Γ‐X crossover.
Determination of the Linear Pressure Coefficients of Semiconductor Bandgaps
Authors: Prins A. D. , Sly J. L. , Dunstan D. J.
Published: July 2007

Measurement of the pressure dependence of the direct bandgap of a tetrahedral semiconductor shows a pronounced sublinearity. This is explained by the stiffening of the lattice under pressure, so that if the pressure is converted into change of lattice constants using a suitable equation of state, the relation between bandgap and lattice constant is found to be linear within experimental (and theoretical) error. However, fitting to the pressure data, many authors use a parabolic equation, Eg(P) = Eg(0) + aP – bP2. We show that this gives a systematic error in the determination of the linear term a which increases with the pressure range of the experiment. GaAs provides a typical example of the systematic error. We find that the true linear pressure coefficient of GaAs is near 11.5 meV/kbar in agreement with the recent low‐pressure measurement of Perlin et al. rather than the long‐accepted value of 10.7 meV/kbar.
Optical Absorption and Raman Scattering Measurements in CuAlSe2 at High Pressure
Authors: Roa L. , Chervin J. C. , Chevy A. , Davila M. , Grima P. , Gonzáez J.
Published: July 2007

The ternary compound CuAlSe2 is a direct energy gap semiconductor (Eg = 2.6 eV at 300 K) crystallizing in the tetragonal chalcopyrite structure. In this work the optical absorption edge and the Raman active modes of CuAlSe2 were measured as a function of pressure up to 30 GPa. The measurements were performed in a membrane diamond‐anvil cell at ambient temperature using neon gas as pressure transmitting medium. The direct energy gap (Γ → Γ) increases linearly with pressure at the rate of 4.7 × 10−2 eV GPa−1. At 6.7 GPa the character of the fundamental gap changes to pseudodirect (Γ → Γ). This gap decreases with pressure at a rate of −2.9 × 10−2 eV GPa−1. The effect of pressure on the phonon frequencies is discussed in terms of the Grüneisen parameters. A first‐order structural phase transition was observed at 12 GPa in the upstroke and at 2 GPa in the downstroke.
Transverse Acoustic Phonons of Germanium up to 9.7 GPa by Neutron Inelastic Scattering
Authors: Klotz S. , Besson J. M. , Braden M. , Karch K. , Bechstedt F. , Strauch D. , Pavone P.
Published: July 2007

Recent progress in high pressure neutron techniques now permits the measurement of the phonon dispersion curves of germanium at pressures up to 10 GPa. Inelastic neutron scattering measurements on 25 mm3 single crystals have been performed for the first time up to 9.7 GPa, that is close to its pressure‐induced phase transition. Frequency variations of the phonon modes were measured along the [100], [110], and [111] directions and are shown to have a nonlinear volume dependence for all wavevectors. These results are compared with published data on the behaviour of TA modes in tetrahedral semiconductors and with recent calculations using the density functional formalism. The agreement between experiment and theory is remarkable and underlines the potential of ab initio calculations for accurately describing the lattice dynamics of semiconductors at variable density.
Shubnikov‐de Haas Effect in (Cd1−x−yZnxMny)3As2 under Pressure
Authors: Laiho R. , Lisunov K. G. , Shubnikov M. L. , Stamov V. N. , Zakhvalinskii V. S.
Published: July 2007

We have investigated the Shubnikov‐de Haas effect in single crystals of the group II‐V diluted magnetic semiconductors (Cd1−x−yZnxMny)AS2(x + y = 0.3, y = 0.06 and 0.08) at temperatures T = 4.2 to 16 K and magnetic fields B = 0 to 6.5 T under hydrostatic pressure p up to 14 kbar. Values of the cyclotron mass mc, the effective g‐factor g*, and the Dingle temperature TD have been determined. In both specimens a linear field dependence mc(B) = m + αB is observed, where m is independent of B but increases with pressure and where a does not depend on p and B. Additionally, pressure dependencies of g*, TD and the Hall mobility μR are observed. The dependence of m and g*, on p is interpreted within the three‐band Kane model. The decrease of μR and TD with increasing pressure is consistent with an increase of m.
Far Infrared Spectroscopy of Semiconductors at Large Hydrostatic Pressures
Authors: Haller E. E. , Hsu L. , Wolk J. A.
Published: July 2007

The combination of high resolution far infrared spectroscopy and large hydrostatic pressures produced by diamond anvil cells (DAC) offers a unique approach to the study of dopants, defects, and bandstructure related properties of semiconductors. The problem of small optical throughputs typical of DACs has been solved. Using this unique tool, we have obtained several new results, including the discovery of a local vibrational mode of the DX center in GaAs:Si and the demonstration that the DX center is a negative‐U defect. We have also discovered the first evidence of DX centers in InP and studied the ground to bound excited state transitions of shallow impurities in GaAs at pressures at which GaAs is an indirect bandgap semiconductor with its conduction band minimum near the X symmetry point.
Identification of the L‐Band in InxGa1−xP/In)0.5Al0.5P Multiple Quantum Wells from High Pressure Measurement
Authors: Patel D. , Interholzinger K. , Thiagarajan P. , Robinson G. Y. , Menoni C. S.
Published: July 2007

High pressure photoluminescence measurements used to study the band structure of the InxGa1−xP/In0.5Al0.5P (x ⩽ 0.48) multiple quantum wells revealed that in narrow‐lattice‐matched and highly tensile strain structures the L1c band is the lowest conduction band state. The L1c minimum was identified as it shifted with pressure at a rate of (60 ± 5) meV/GPa, considerably smaller than that of the direct gap Γ1c states.
Alternative Method for Determining the Shear Deformation Potential of the Valence Band in III‐V Semiconductor Quantum Wells
Authors: Rau G. , Klipstein P. C. , Nicopoulos V. Nikos , Johnson N. F. , Tribe W. R.
Published: July 2007

We present an alternative method for determining the shear deformation potential b of the valence band in III‐V semiconductors. Instead of bulk semiconductors we use quantum well structures and apply uniaxial stress perpendicular to the growth direction. Using analytical solutions we show that the first confined hole state has a pronounced and characteristic nonlinear energy shift with respect to stress. This allows the hydrostatic and shear deformation potentials a and b to be determined independently from the stress dependence of the bandgap only, which can be measured by a wider range of experimental techniques than those necessary for obtaining deformation potentials from bulk material. Measurements on a (GaAs)10/(AIAs)10 superlattice yielded a value for b which is in good agreement with recent results from bulk measurements and hence support the validity of our proposed method.
Determination of Gain and Loss Mechanisms in Semiconductor Lasers Using Pressure Techniques
Authors: O'Reilly E. P. , Jones G. , Silver M. , Adams A. R.
Published: July 2007

Both the gain and loss mechanisms in semiconductor lasers are determined in large part by the band structure of the laser active region and the surrounding material layers. Uniaxial stress measurements confirm the predicted variation of gain and threshold characteristics due to the incorporation of axial strain, with large tensile or compressive strain reducing the carrier and current density required to reach threshold. The combination of hydrostatic pressure measurements and band structure calculations enables identification of the dominant loss mechanisms in semiconductor lasers, identifying leakage from the active to the cladding region as the dominant loss mechanism in GaInP/AIGaInP visible lasers, and Auger recombination as the dominant loss mechanism and cause of the temperature sensitivity of long wavelength (1.3 to 1.55 μm) lasers.
Raman Scattering and Photoluminescence of Mn‐Doped Nanocrystals of ZnS Formed by the Pressure Cycle Method
Authors: Kobayashi M. , Iwata H. , Hanzawa H. , Yoshiue T. , Endo S.
Published: July 2007

Zn1−xMnxS (x = 0.043) undergoes a pressure‐induced phase transition at 14.1 GPa from the zincblende to the NaCl structure. We have measured Raman scattering for a pressure released sample after compressing up to 16 GPa in a diamond anvil cell. The LO peak has shifted to lower energy compared with a virgin sample, which indicates the quantum confinement of LO phonons in nanocrystals formed by the pressure cycle. The diameter of nanocrystals is estimated to be 8 nm according to the spatial correlation model, in agreement with the value estimated from X‐ray diffraction data. The observed decrease of photoluminescence intensity and the shortening of the decay time for the 4T1 → 6A1 transition within the Mn2+ ion are ascribed to the formation of nonradiative centers in the nanocrystals.
High‐pressure Raman Scattering and Optical Absorption Study of β‐GeS2
Authors: Popović Z. V. , Holtz M. , Reimann K. , Syassen K.
Published: July 2007

We have measured Raman scattering and optical absorption spectra of layered β‐GeS2 at pressures up to 15GPa. Frequency shifts of selected internal bond bending and stretching modes are discussed, and three external (rigid‐layer) modes are identified. Changes in the Raman spectra near 9 GPa clearly indicate a structural phase transition. The pressureinduced red shift of the optical absorption edge shows a change in slope at about the same pressure. Samples turn opaque near 15 GPa, indicating a second transition to a disordered phase. The pressureinduced phase changes are reversible.
Kinetic Features of Crystallization of Cubic Boron Nitride Single Crystals in the BNLiH(N,Se) System
Authors: Gameza L. M. , Shipilo V. B. , Savchuk V. A.
Published: July 2007

We have investigated the effect of selenium additions on the kinetics of the degree and rate of hexagonal to cubic BN conversion (hBN → cBN) as well as on the linear rate of the cBN crystal growth in the BN‐LiH(N,Se) system. Experiments were performed in the temperature range 1940 to 2080 K at a pressure of 4.3 GPa. For 0.5, 1.0, and 3.0 mass% selenium addition, the activation energy of the process of cBN formation is found to be 45.0, 39.0, and 34.0 kJ/mol, respectively. The resulting crystals showed n‐type conduction with a resistivity of 105 to 108 Ω cm and a dislocation density of 105 to 103 cm−2.
Emission of a Half‐Rectangular Dislocation Loop from a Mode I Crack Tip
Authors: Zhang Tong‐Yi
Published: July 2007

Energies for emission of a half‐rectangular dislocation loop from a mode I crack tip are investigated in the present work. Optimum aspect ratio of length to width of the half‐rectangular loop, critical dislocation size, and activation energy for dislocation emission are calculated by determining the saddle point of the total energy profile as a function of the length and the width. The activation energy obtained for the half‐rectangular loop is less than a quarter of that obtained for a semicircu‐ lar loop. The effects of the self‐energy correction parameter and the radius of the dislocation core on the activation energy are also reported here.
Modeling of Threading Dislocation Density Reduction in Heteroepitaxial Layers I. Geometry and Crystallography
Authors: Romanov A. E. , Pompe W. , Beltz G. , Speck J. S.
Published: July 2007

The geometry of threading dislocations (TDs), non‐equilibrium defects that are generated as a result of stress relaxation in thin films, is considered in order to provide a basis for their reduction behavior during heteroepitaxial growth. This paper, the first of a two‐part series, discusses the geometric possibility for reactions between TDs as a result of film growth. It is demonstrated that effective TD motion and reaction are responsible for their overall reduction. The reactions become possible if pairs of TDs come within a critical distance: γA for annihilation reactions, γF for fusion reactions, and γS for scattering reactions. The model is used to explain the experimentally observed l/h (h is the film thickness) dependence on TD density. The crystallographic consideration of TDs in the case of (001) growth of f.c.c. semiconductor films is presented and possible reactions between TDs in this case are analyzed.
First Principle Calculations of the Basic Thermodynamic Properties of Titanium and Vanadium Nitrides
Authors: Milevskii A. G. , Lisenko A. A. , Morozov M. M. , Zhurakovskii E. A.
Published: July 2007

In this paper we present the results of volume and thermal dependent energy calculations for a binary system using density functional theory based on APW electronic structure calculations as well as the Debye model for accounting for lattice vibrations. Our APW calculations of ground state equilibrium properties of TiN and VN are close to those obtained by the LMTO method but are in better agreement with experiment. By minimization of the resulting free energy with respect to volume we obtained temperature dependent lattice parameters and coefficients of thermal expansion.