bluuebunny/crossref_metadata_2025_split huggingface dataset:
Infrared Absorption in Anharmonic Crystals with Impurities: An Application to a Diatomic Linear KI‐Chain
Authors: Held Th. , Kuhn W. , Pfeiffer I. 
Published: July 2007

AbstractIn expansion of well‐known results of dynamic and optical properties of anharmonic ideal crystals, a perturbation theory, using Matsubara functions and diagrammatic treatment is carried out to describe anharmonic crystals with impurities. Taking explicity into account anharmonic contributions of the potential expansion up to fourth order, mass changes as well as force constant changes between impurity and host‐lattice particles, it is shown that the anharmonic phonon propagator can be written as a sum of terms, which are added up within a Dyson equation. The corresponding proper self‐energy includes impurity‐activated harmonic as well as impurity‐influenced anharmonic contributions. As an application the infrared absorption of a diatomic linear KI‐chain with next‐neighbour interaction, a single mass defect, and consideration of anharmonicities up to second order of the van Hove parameter (O(α2)) is chosen. Numerical calculations of temperature‐dependent lineshapes and shifts of defect and main absorption lines are presented and discussed together with results of defect‐induced in‐band absorption.
Analysis of Free Exciton Properties in GaAs Epitaxial Layers with the Improved Model of Photoconductivity Spectra
Authors: Wu Fencmei , Shi Yi , Parenteau M. , Jorio A. , Carlone C. 
Published: July 2007

AbstractThe transition energy, binding energy, intensity, broadening, and lifetime of the free‐exciton transitions in GaAs epitaxial layers are well investigated experimentally and theoretically. The improved model of photoconductivity spectra which accounts for the contribution of many excitonic levels and two broadening mechanisms is presented. Moreover, the variation of the free‐exciton properties with increasing epitaxial layer thickness is discussed.
Temperature Dependence of Exchange Narrowed ESR Linewidth of (MT)2(TCNQ)3·2 H2O Salt
Authors: Koshta A. A. , Graja A. 
Published: July 2007

AbstractThe electron spin resonance g‐factor, linewidth, and spin susceptibility of single crystals of the (MT)2(TCNQ)3·2 H2O salt are presented. A discussion of the ESR parameters is given. It is shown that the exchange narrowing mechanism determines the lineshape as well as its temperature and orientation dependencies.
Deflection of Laser Light by an Acoustic Wave in a Magnetised Semiconductor with High Dielectric Constant
Authors: Pragya D. , Ghosh S. 
Published: July 2007

AbstractAn analytical investigation is made for the scattering of laser light by an acoustic wave propagating obliquely to the externally applied magnetic field in a doped solid state plasma with high dielectric constant, consequent amplification of scattered modes is also carried out. The origin of this nonlinear interaction lies in the second‐order optical susceptibility arising due to the nonlinear current density in the medium. The influence of carrier density is also considered. The threshold value of the pump electric field is obtained. It is found that the threshold pump amplitude required for the onset of instability may be reduced by increasing the doping level and decreasing the obliquity of the magnetic field to the propagation direction. The steady state growth rate is also obtained. The gain constant increases explosively with a little increment in cyclotron frequency after it touches its minimum at ωc≈1013 s−1. The transmitted intensity of the scattered mode and the cell efficiency have also been decuded when the cell length is quite large compared to the pump wavelength. The transmitted intensity is found to have a maximum value when the magnetic field is applied at an angle of 60° to the photon propagation direction.
Plasmons in CaSO4
Authors: Yaskolko V. Ya. 
Published: July 2007

AbstractWith the help of optical loss spectra (OLS), energy loss spectra (ELS), and the dependence of stimulated electron emission on the energy of slow exciting electrons (ESEL), the true plasmon energies in CaSO4 (13.5, 18.1,20.9 eV) are obtained and the energy gap is confirmed (12 eV). The subzones in the valence band where plasma oscillations occur are determined, as well as the number of electrons in one plasmon. The band structure for CaSO4 is constructed and interband transitions are interpreted. From the data of CaSO4 the plasmon energies, the energy gaps, etc. for the Sr, Ba, Pb sulphates are calculated.
Reference System Approach in the Electron Liquid Theory: V. Application to the Two‐Component Fermi Systems
Authors: Vavrukh M. , Blazhievskii O. 
Published: July 2007

AbstractThe reference system approach developed in the electron liquid theory is generalized for the case of the two‐component Fermi system model with a long‐range interaction between particles. The degenerate subsystems of non‐interacting particles are considered as a reference system. The general relations are shown for a simple model, i.e. degenerate electroneutral two‐component Fermi system model of charged particles. Some energetic and structural characteristics of this strongly non‐ideal model in the metal phase are obtained.
Novel Slab Model Analysis for Overlayer Deposited Bent Step‐Index Single‐Mode Fiber Half‐Couplers
Authors: Haubenreisser W. , Ecke W. , Schröter S. , Schwotzer G. , Wjllsch R. 
Published: July 2007

AbstractA Novel Slab Model (NSM) for the modal analysis of Overlayer (OL) deposited Bent Step‐Index Single‐Mode Fiber (BSSF) half‐couplers is presented. In this NSM the BSSF is replaced by a modal equivalent slab waveguide (ESW) structure. It is shown that within the framework of the NSM the modal features of actual OL‐BSSF structures can be described more correctly and consistently on the basis ofequivalent OL‐ESW structures. A perturbation method is developed to analyze modal properties of such OL‐ESW structures analytically. Our modal analysis comprises all hitherto investigated evanescent fiber‐optic devices based on OL‐BSSF structures.
On the Theory of Reflectivity by an X‐Ray Multilayer Mirror
Authors: Kohn V. G. 
Published: July 2007

AbstractA general theory of reflectivity by a perfect X‐ray multilayer mirror based on the usage of a recurrent relation is developed. The reflectivity is described by the well‐known Fresnel formulae which take into account jumps of susceptibility at the boundary between the layers. The analytical solution in the frame of the most general dynamical approach is found and the condition of application of the kinematical approximation is discussed. Special attention is paid to the periodic multilayer structure containing two layers of different materials with more than one pair of these layers in the period.
Angle‐Resolved Photoemission Investigation of the Valence Bands of RuCl3
Authors: Carricaburu B. , Mamy R. , Pollini I. 
Published: July 2007

AbstractThe electronic structure of the layered compound RuCl3 is studied by means of X‐ray photoelectron spectroscopy and angle‐resolved ultraviolet photoelectron spectroscopy. The energy distribution curves are measured along different azimuthal directions ΓM, ΓM′, and ΓK in the Brillouin zone. The experimental valence bands of RuCl3 consisting of an uppermost non‐dispersive band of d symmetry at about 2 eV above the top of the valence p band, and two dispersive bands of p symmetry are studied by application of the E(k‖) method. The nature of the valence bands of RuCl3, are discussed in relation to the electronic structure of the metal RuO2 owing to their similar X‐ray photoelectron spectra.
On the Analytical FMR Theory in the Normal Configuration
Authors: Fraitová D. 
Published: July 2007

AbstractThe analytical expressions for dispersion relations, cross‐over effect conditions, effective penetration depth, surface impedance, and inflection linewidth for FMR in bulk metals in normal configuration are derived including electrical conductivity and the Landau‐Lifshits damping parameter (for the case of zero surface pinning). The possibility of excitation of Larmor and anti‐Larmor Kittel and surface modes in materials with negative surface anisotropy is investigated.
57Fe Mössbauer Spectra Study on Eu0.5RE0.5Fe0.5Mn0.5O3 Oxides
Authors: Li Liping , Wei Quan , Ren Xiaolin , Li Wancheng , Su Wenhui 
Published: July 2007

AbstractThe method of solid state reactions is used to synthesize the samples of Eu0,5RE0,5Fe0,5Mn0,5O3 (RE = La, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Y). XRD and 57Fe Mössbauer spectra are measured. It is found that the volume of the unit cell of the samples decreases with increasing atomic number of RE. The Fe ions are in the Fe3+ high spin state, and the relationship between the quadrupole splittings and the lattice distortion parameter D of the samples is linear.
Optical Oscillations and Their Peculiarities Caused by Internal Switching Delay in Optically Bistable CdS Crystals
Authors: Kažukauskas V. , Issler H. , Grohs J. , Klingshirn C. 
Published: July 2007

AbstractLight oscillations due to internal switching delay in optically bistable CdS platelets are reported using a geometry with two exciting beams. It is shown that in the case when one of the exciting beams has the form of a long thin light strip, an internal delay occurs due to the final propagation speed of the bistable switching front along it (switching wave) which enables one to obtain oscillations using electrooptical feedback without external delay. If an external delay is applied to one of the beams, while the second one appears as a single light pulse peculiarities of the oscillations caused by the interaction of both delay signals are obtained, which are not observed if only one light beam is used.
Optical Properties of Undoped and V‐Doped VA−VIA−VIIA Single Crystals
Authors: Park Sang‐An , Kim Mi‐Yang , Lim Ji‐Young , Park Byong‐Seo , Koh Jeong‐Dae , Kim Wha‐Tek 
Published: July 2007

AbstractSbSI:V, SbSeI:V, BiSI:V, and BiSeI:V single crystals are grown by the vertical Bridgman technique using ingots synthesized from mixtures of the elements (purity 99.9999%). The grown single crystals have an orthorhombic structure and an indirect energy band structure. The temperature dependence of the optical energy gap is well fitted by the Varshni equation. Impurity optical absorption peaks due to the doped vanadium appear and are assigned to the electron transitions between the energy levels of the V2+ ion located at Td sites of the host lattice.
Blue‐Green ZnSe Laser Diodes for Optoelectronics. Present State at Würzburg University
Authors: Landwehr G. , Hommel D. 
Published: July 2007

AbstractA review is given on the research activities at Würzburg University in the field of blue‐green emitting ZnSe laser diodes. Of great importance for both the structural and electrical properties is the possibility to grow a GaAs buffer layer on the GaAs substrate prior to the II–VI growth. Pulsed room temperature lasing with a duty cycle up to 17% is obtained using quaternary ZnMgSSe cladding layers, ternary ZnSSe waveguides, and a single CdZnSe quantum well. Important issues for long‐term stability of such laser diodes like growth start, p‐type doping, and ohmic contacts are discussed.
Growth Kinetics in MOMBE‐ALE of ZnSe and CdSe as Determined by a New In‐Situ Optical Probing Method
Authors: Yoshikawa A. , Kobayashi M. , Tokita S. 
Published: July 2007

AbstractThe surface reaction mechanism in MOMBE‐ALE of ZnSe and CdSe using DMZn, DMCd, and H2Se as reactants is studied with a newly developed optical in‐situ monitoring method. The new method is named surface photo‐interference (SPI), because the concept of the SPI is essentially concerned with a photo‐interference in the heteroepilayer. Fairly low‐energy photons for which the epilayer is transparent can be used as probing light in SPI. Reflecting this feature, SPI is especially useful for studying heteroepitaxial growth kinetics of wide‐gap II‐VI compounds, because the effect of photocatalytic growth rate enhancement can be avoided when using such low energy photons as probing light. It is shown that there is a quite significant difference in the surface reaction mechanism between the MOMBE‐ALE of ZnSe and CdSe. That is, in the ALE of ZnSe when none of the source gases are per‐cracked, the reaction to form ZnSe can take place when the group‐II source (i.e., DMZn) is supplied, resulting in an alternate appearance of Zn terminated and H2Se terminated surfaces during growth. On the other hand, the reaction to form CdSe can do when the group‐VI source (i.e., H2Se) is supplied, resulting in an alternate appearance of Se terminated and DMCd terminated surfaces during growth.
Raman Scattering by Acceptors and Donors in p‐Type ZnSe
Authors: Davies J. J. , Wolverson D. , Boyce P. J. 
Published: July 2007

AbstractRaman spectroscopy is used to study dopants introduced into ZnSe to produce p‐type material. Special attention is paid to nitrogen‐doped epitaxial layers and Raman scattering involving the electronic levels of nitrogen acceptors is reported. In these layers spin‐flip scattering by electrons at a new type of donor centre at a depth of about 50 meV is also observed. This new donor is believed to play an important role in the compensation process that limits the net acceptor concentrations attainable in this material.
Optimization of Ohmic Contacts to ZnSe by Parabolic Grading of ZnSe1−xTex Composition
Authors: Yang G. L. , Luo H. , Lewandowski L. , Furdyna J. K. 
Published: July 2007

AbstractA new type of grading, namely, parabolic grading, for the purpose of improving ohmic contacts to p‐type ZnSe is presented. The valence band profiles as well as the critical grading length for a 1kT barrier are calculated for a parabolically graded Zn(Se, Te) structure. Comparison of our results with those of linearly graded structures shows the clear advantage of parabolic grading.
Effective Mass Theory for Strained Superlattices
Authors: Brezini A. , Hamdache F. , Behilil F. , Depollier C. 
Published: July 2007

AbstractAn exact model calculation for the band structure based on the one‐dimensional Kronig‐Penney model including the local potential induced by the monolayers, is developed and compared to the conventional one. Although it is formulated for strained superlattices, it may be generalized to any abrupt strained heterostructures.
A New Approximation for Block Diagonalizing the Eight‐Band k · p Hamiltonian
Authors: Enders P. 
Published: July 2007

AbstractKane's (1957) coordinate transformation for diagonalizing the eight‐bank k · p Hamilton matrix for GaAs‐like semiconductors into 4 × 4 blocks is reexamined, where the k2−terms (free electron and interaction with the remote bands) are taken into account fully, not only perturbatively. Then, the warping precludes an exact block diagonalization. A new approximation is proposed which allows for a 4 × 4 block diagonalization, again. Since this approximation preserves the cubic symmetry and its error vanishes along the symmetry directions (k ‖ [100], [110], [111], etc.), it remains small for general k‐directions. This is illustrated by numerical examples. The 4 × 4 block diagonalization allows for significant simplifications in calculating the band structure and related properties. In contrast to other approaches, a consistent calculation of the momentum matrix remains possible.
Hot Electron High‐Frequency Mobility in Wide‐ and Narrow‐Gap Semiconductors
Authors: Weng X. M. , Lei X. L. 
Published: July 2007

AbstractHot electron High‐frequency mobility in wide‐ and narrow‐gap semiconductors under the influence of a small ac electric field superimposed on a dc bias electric field using the balance equation theory recently developed for an arbitrary energy band is investigated. In the wide‐gap semiconductor SiC the frequency dependent mobility predicted by the balance equation approach is not in quantitative agreement with a previous calculation based on the Boltzmann equation with a displaced Maxwellian distribution function. In narrow‐gap semiconductors it is found that nonparabolicity strongly affects the frequency dependence of the hot‐electron small signal mobility, such that the curves of the real and imaginary parts of the ac frequency in a strongly nonparabolic system (InAs) appear completely different from those in a weakly or moderately nonparabolic system (GaAs).
Energy Loss Rate of Hot Electrons in n‐HgxCd1−xTe at High Temperatures in the Presence of a Quantizing Magnetic Field
Authors: Bhaumik S. , Sarkar C. K. 
Published: July 2007

AbstractThe energy loss rate of hot electrons due to longitudinal polar optical phonons in narrow‐gap semiconductors is calculated for the longitudinal configuration with classical and quantum screening for various lattice temperatures. The results are used to examine the influence of quantum screening on the energy loss rate. A relative comparison of the effects of quantum and classical screening on the energy loss rate due to optical phonons is made. The energy loss rate without screening is compared with the energy loss rate with classical and quantum screening.
Effective Magnetic Moments of Co and Fe Clusters
Authors: Mahendran M. , Iyakutti K. 
Published: July 2007

AbstractThe effective magnetic moment per atom, μeff, is calculated for ferromagnetic clusters of cobalt and iron in the mean‐field approximation. μeff is also computed by assuming that the clusters undergo superparamagnetic relaxation. The surface effects are included properly. The calculated μeff are in agreement with recent experimental results. The characteristic features of this study are: 1. μeff of these clusters are far below the bulk values of Co and Fe and 2. the exchange interaction and the internal magnetic field attain saturation as the cluster size increases.
Experimental verification of the new model for the two‐photon absorption of biexcitons in CuCl
Authors: Hasuo M. , Kawano H. , Nagasawa N. 
Published: July 2007

AbstractTwo different theoretical models of the giant two‐photon absorption due to excitonic molecules (xx) are examined experimentally. The conventional model (Hanamura, 1973) follows the sequence: photon + photon → exciton + photon → xx, while the self‐consistent model (Ivanov and Haug, 1993) gives the other scenario of the two‐photon absorption: photon + photon → exciton + exciton → xx. Our high‐precision measurement of the frequency dependence of the two‐photon xx absorption coefficient in CuCl allows us to discriminate these two models and supports the new self‐consistent model.
Photoinduced Fermi‐edge singularity in one‐dimensional semiconductors
Authors: Ogawa T. 
Published: July 2007

AbstractA high‐density electron–hole system in one dimension (1D) is studied theoretically in terms of the photoinduced Fermi‐edge singularity (FES) in optical spectra, the anomaly of which results from the fluctuating exciton Bose condensation in 1D. Describing this system as the two‐band Tomonaga Luttinger (TL) liquid with the forward‐scattering correlations, the critical exponent of the FES is analytically obtained with the aid of the bosonization technique. Competition between the exciton condensation and other Fermi‐surface instabilities is also clarified within the framework of the two‐band g‐ology. Comparison with the FES in ordinary 1D conductors (heavily‐doped 1D semiconductors), which are described as the single‐band TL liquids, is made to clarify recoil effects of an optical hole on the FES. Effects of backward scatterings, random potentials, spin‐dependent electronic correlations, and spin splitting of the conduction band are also discussed.
Theory of plasmon‐assisted electron pairing in semiconductors
Authors: Blank R. , Haug H. 
Published: July 2007

AbstractIt is shown that plasmon‐assisted superconductivity can occur in an electron plasma of a modulationdoped quantum well structure or in an optically excited, cool quasi‐equilibrium electron–hole plasma in stressed quantum wells. For our analysis the quasi‐classical approximation (QCA) for non‐equilibrium Keldysh‐Green functions for carriers of a degenerate plasma is used. The screening is described in RPA, simplified further for some of the calculations by a damped plasmon‐pole approximation (PPA). Because the plasmon coupling is strong the appropriately modified Eliashberg equations are derived and analyzed for the complex frequency‐dependent normal and anomalous self‐energies. The plasmon frequency in a semiconductor plasma with a typical density of 1018 cm−3 is of the order of some 10 meV. If the spectral density of the plasmon is not too broad, a pairing instability is found also in the range of interparticle distances with rs < 1, where QCA and RPA are valid. Depending on the material, transition plasma temperatures of up to 30 K are obtained which can be enhanced further by quantum confinement and special properties of the band structure. The underlying virtual exchange of plasmons can only be obtained in a fully dynamical description, and is absent in the commonly used quasi‐static quasi‐particle approximations.
Excitonic nonlinearities and gain processes in binary and ternary ZnSe‐based quantum well structures
Authors: Lowisch M. , Kreller F. , Puls J. , Henneberger F. 
Published: July 2007

AbstractThe nonlinear optical properties of MQW structures with binary (ZnSe/ZnMnSe) and ternary (ZnCdSe/ZnSe) wells grown by MBE are compared. Pump‐probe experiments and high‐excitation PL measurements are carried out to study the excitonic nonlinearity as well as gain processes. It is found that the nonlinear optical response is qualitatively different in these two structures as a result of the different kinds of disorder present in the QWs.
Controlled spontaneous emission from semiconductor microcavities
Authors: Yamanishi M. 
Published: July 2007

AbstractThe advantages of the simultaneous quantum manipulation of electron and photon systems due to quantum‐confined Stark effect and cavity quantum electrodynamics, respectively, in semiconductor microstructures are clarified, manifesting systematic experimental results on high transfer efficiencies of spontaneous emissions and cavity‐induced fractional changes of exciton decay times around on‐axis resonance. The scheme for the simultaneous quantum manipulation is also expected to lead to attractive device concepts for highly efficient, high‐speed spontaneous light emitters, and sub‐Poissonian photon generators in a short time interval.
Saturation and losses in an optical semiconductor quantum well amplifier
Authors: Butty J. , Bongiovanni G. , Staehli J. L. 
Published: July 2007

AbstractThe results obtained from luminescence measurements made on one‐dimensional optical amplifiers
are reviewed. The investigated samples are GaAs/(Ga, AI)As waveguiding structures containing a
multiple quantum well structure as active element. The experimental data are compared with the
results of a numerical self‐consistent model of the optical amplifier. The observed spatial dependencies
of carrier and luminous densities are found to agree in a semi‐quantitative way with the theoretical
predictions. Saturation of optical amplification is caused by carrier depopulation through stimulated
recombination, and by the loss of light caused by scattering at sample defects and/or imperfect
waveguiding. It is argued that the discrepancies found on the high‐energy side of the grain spectra are
caused by reabsorption of amplified light at the edges of the amplifier.