bluuebunny/crossref_metadata_2025_split huggingface dataset:
Optical interband properties of some semiconducting silicides
Authors: Lange H. , Henrion W. , Fenske F. , Zettler Th. , Schumann J. , Teichert S. 
Published: July 2007

AbstractOptical transmission and reflection as well as ellipsometric studies are performed for the semiconducting phases CrSi2, MnSix, and Ir3Si5 in the energy region from 0.2 to 5.0 eV. Onsets of strong interband transitions are found around 0.5 eV for the former two compounds and 1.2 eV for the latter one. Optical data analysis for the former two compounds suggests them to be indirect semiconductors whereas for the latter to be a direct one. Main interband features for CrSi2 and MnSi1.73 appear between 1 and 2 eV and for Ir3Si5 at 3 eV. An explanation of these findings is given in terms of existing band structure and density of states considerations.
Optical anisotropy in superlattices as a consequence of dielectric mismatch
Authors: Jahne E. 
Published: July 2007

AbstractThe “bulk‐slab” continuum model for the dielectric function of a superlattice is reconsidered. It is demonstrated how the optical anisotropy of the effective medium depends on the dielectric mismatch between the layers. As examples the dielectric mismatch and layering‐induced anisotropy are studied for both phonon and electronic interband excitations in GaAs/AlAs and GaSb/InAs superlattices. It turns out that the dielectric mismatch and hence the anisotropy for phonon excitations is large in comparison to that for electronic interband transitions. Angular dependencies of longwavelength optical phonons for long period superlattices are derived from the angular dependence of the dielectric function of the extraordinary ray in the effective medium.
Extended novel slab model analysis of overlaid bent step‐index single‐mode fiber half‐couplers. I. Basic formalism and normal‐mode approach
Authors: Haubenreisser W. , Ecke W. 
Published: July 2007

AbstractAn extended novel slab model (ENSM) in strong guidance approximation (SGA) is presented for the modal analysis of overlaid bent step‐index single‐mode fiber half‐couplers (OL‐BSSF) where now proper (bound) and leaky modes are included as well. Within the frame of ENSM and SGA a basic formalism is elaborated to evaluate the propagation characteristics as well as the dissipative and/or leakage propagation losses of OL‐BSSF structures in a great measure analytically. The powerfulness of the formalism is demonstrated on a six‐layered OL‐BSSF/ESW basic structure with a general three‐layered overlay (OL) where the BSSF structure is mapped modally by an equivalent slab waveguide (ESW) structure. Such a multilayered slab basic structure can describe the modal and optical features of all hitherto implemented configurations of all‐fiber in‐line components as special cases straightforwardly based on OL‐BSSF structures.
Covalent mechanism of cooperative optical transitions in lanthanide exchange‐coupled pairs. Intensity calculations for double transitions in a M2L11 f1–f1 dimer
Authors: Mironov V. S. , Kaminskii A. A. 
Published: July 2007

AbstractThe covalent mechanism of cooperative optical transitions in exchange‐coupled pairs of lanthanide ions (which is closely related to the magnetic superexchange mechanism) is analyzed in detail for a simple M2L11 f1–f1 model dimer (two ML6 octahedra sharing one bridging ligand L). New effective electron transfer pathways in the M(A)–L–M(B) exchange system are considered and intensities of cooperative transitions from the (00) ground state to (ij) doubly‐excited states of the f1–f1 dimer are calculated including polarization effects.
Efficient 2 μm stimulated emission in the 4F9/2 → 4I11/2 channel from monoclinic BaYb2F8: Er3+ crystals
Authors: Kaminskii A. A. , Butashin A. V. , Mironov V. S. , Bagaev S. N. , Eichler H.‐J. 
Published: July 2007

AbstractNew spectroscopic and laser data on monoclinic Ba(Yb1−xErx)2F8 crystals are obtained. Efficient 2 μm stimulated emission of Er3+ ions in the 4F9/2 → 4I11/2 channel and 2 and 3 μm cascade lasing of the sequential 4F9/2 → 4I11/2 → 4I13/2 transitions were excited at room temperature under Xe flashlamp pumping. Intensity characteristics of manifold‐to‐manifold (JJ′ transitions) such as Einstein coefficients AJJ, line strengths sJJ′, branching ratios βJJ′, and radiative lifetimes τrad for the initial laser states 4I13/2, 4I11/2, 4I9/2, 4F9/2, 4S3/2, and 2H(2)9/2 were analyzed in detail. All observed laser transitions between individual Stark levels were identified. Unlike well‐known 2 μm lasers with Ho3+, Tm3+, Co2+, and Ni2+ ions in many oxide and fluoride compounds, BaYb2F8: Er3+ crystals operate on a pure four‐level generating scheme.
Field domains in semiconductor superlattices
Authors: Schwarz G. , Schöll E. 
Published: July 2007

AbstractField domain formation in the regime of vertical high‐field transport in semiconductor superlattices is studied theoretically. Depending upon the mean doping density ND, either stable stationary domains (for high ND), or self‐sustained oscillations of the domains (for intermediate ND) are found. Our simulations show that this behaviour is strongly affected by growth‐related imperfections like small fluctuations of the doping density, and that weak disorder on microscopic scales can be quantitatively detected by the global macroscopic current‐voltage characteristics. The role of the different realizations of the microscopic disorder and different boundary conditions are discussed. Equal areas rules for domain formation are derived under simplifying approximations.
Transport properties of high‐Tc mercury cuprates
Authors: Onbasli Ü. , Wang Y. T. , Naziripour A. , Tello R. , Kiehl W. , Hermann A. M. 
Published: July 2007

AbstractMeasurements of dc and ac susceptibility, resistivity, Hall effect, and thermoelectric power (TEP) on pure phase Hg‐1223 and mixed phase Hg‐1212–1223 cuprates are reported. The mixed phase compounds show the highest critical temperature (magnetic susceptibility onset of 138 K). Both Hall effect and TEP data support an underdoped state with hole‐like conduction. Oxygen annealing reduces the Hall coefficient (increasing the concentration of holes) and lowers the TEP (increasing the Fermi energy) features which can be explained by a simple Fermi‐gas picture. The Hall coefficient which increases linearly with temperature and the negative temperature coefficient of the TEP, however, cannot be explained by single‐band Fermi‐gas or ‐liquid theory, unless one introduces energy dependent carrier scattering. Estimates of the highest critical temperature based on the universality observed in the thermopower data for the cuprates suggest that 138 K is near the maximum one might expect for the Hg cuprates under optimal doping at atmospheric pressure.
Coherent and conventional quantum 1/f effect
Authors: Handel Peter H. 
Published: July 2007

AbstractThe 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

AbstractThe 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

AbstractTwo‐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

AbstractThe 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

AbstractIt 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

AbstractAt 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

AbstractFor 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

AbstractNeutron 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

AbstractLarge‐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

AbstractHighly 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

AbstractThe 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

AbstractThe 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

AbstractThe 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

AbstractHall 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

AbstractLow 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

AbstractThe 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

AbstractThe 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

AbstractWe 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

AbstractMany‐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

AbstractBased 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.