bluuebunny/crossref_metadata_2025_split huggingface dataset:
Photoemission Calculations Including Both Band Structure Effects and Photon Field Variation
Authors: Das P. , Kar N. 
Published: July 2007

AbstractPhotoemission cross‐sections are calculated, using band wave functions and a spatially varying photon field. The solid is considered to be composed of a stack of identical layers of atoms parallel to the surface with a potential of muffin‐tin form. The photoemission matrix element is calculated by appropriate expansion of the initial and final state wave function and the vector potential of the photon field in the muffin‐tin, interstitial, and vacuum regions. The case of normal photoemission from the (100) face of aluminium is considered as an application.
Polaritons in multiple quantum wells
Authors: Andreani L. C. 
Published: July 2007

AbstractA description of polariton effects on excitons in multiple quantum wells (MQWs), superlattices (SLs), and semiconductor microcavities is given, which is based on a nonlocal semiclassical theory in a transfer‐matrix formulation. The radiative width in MQWs at k = 0 increases first with the number of wells N, then goes to zero as N → ∞, where stationary polariton states are recovered. A very similar behavior is found by treating the MQW with a local dielectric model. In the SL limit, the exciton‐polariton dispersion at long wavelengths reduces to that of a light wave in a uniaxial material, described by an effective dielectric tensor. Comparing with the bulk, the polariton splitting is increased in SLs, and reduced in microcavities. Nevertheless, polariton effects in microcavities are easily observable, since spatial coherence along the growth direction is not required.
Carrier cooling in intermixed GaAs/ AlGaAs quantum dots and wires using high excitation and transient spectroscopy
Authors: Adler F. , Burkard M. , Schweizer H. , Benner S. , Haug H. , Klein W. , Tränkle G. , Weimann G. 
Published: July 2007

AbstractBuried low‐dimensional integrated dot and wire structures fabricated by masked implantation enhanced intermixing are compared directly. Using high excitation and transient spectroscopy hot carrier effects as well as phase‐space filling in the low‐dimensional structures are observed. The carrier cooling curves of the wires and dots show a bend at about 350 ps which may be an indication of two dominant relaxation mechanisms. The influences of the carrier capture in low‐dimensional systems and the relaxation on the carrier temperature are separated by measurements with different excitation wavelengths.
Ultrafast nonlinear optical response of Fano resonances in GaAs under high magnetic field
Authors: Siegner U. , Mycek M.‐A. , Glutsch S. , Chemla D. S. 
Published: July 2007

AbstractThe coherent dynamics of Fano resonances in GaAs are studied under magnetic field using femtosecond four‐wave mixing (FWM). In this system Coulomb coupling bel ween magnetoexciton and continuum states gives rise to Fano interference. By time‐resolving the FWM signal it is shown that dephasing of the coherent emission from a Fano resonance is dominated by the coupling to the continuum. Unlike Lorentzian resonances, the decay of the time‐integrated FWM signal is not related to dephasing. This surprising behavior is due to the interplay between Fano interference and Coulomb correlation in a semiconductor.
The role of coherence for carrier relaxation in photo‐excited semiconductors
Authors: Kuhn T. , Haas S. , Rossi F. 
Published: July 2007

AbstractThe role played by the dynamics of the interband polarization for the correct description of the generation of carriers by a short laser pulse is investigated. The calculations are based on the semiconductor Bloch equations which are solved by means of a generalized Monte Carlo simulation. It turns out that some of the approaches commonly used for a microscopic modelling of the dephasing process fail in describing correctly the effect of carrier‐carrier interaction in the low‐density limit. By including terms which have the structure of “in‐scattering” terms (vertex corrections) for the interband polarization, the experimentally observed features in the carrier dynamics are well reproduced in the whole density range.
Coherent interband effects in quantum kinetics
Authors: Thoai D. B. Tran , Bányai L. , Reitsamer E. , Haug H. 
Published: July 2007

AbstractThe quantum kinetics of a laser pulse exciting electrons and holes interacting with LO‐phonons is studied in [l] within the generalized Kadanoff‐Baym approximation, but the spectral Green functions are approximated by damped free propagators. After including the Hartree‐Fock coherent terms due to the bare Coulomb interaction, oscillations (“quantum beats”) of the incoherently summed polarization with the LO‐phonon frequency have been found in [2]. Here we include the Coulomb Hartree‐Fock terms as well as the optical pump field selfconsistently for both the spectral and particle functions. This procedure takes the phonon‐assisted transitions and excitonic effects fully into account. Our calculations in three‐dimensional and particularly in two‐dimensional semiconductors show an enhancement of the coherent “quantum beat” effects in the incoherently summed polarization. Further we show that these quantum beats are well resolved in the photon echo signal.
Quantum kinetics of the coupled carrier‐phonon system in photoexcited semiconductors
Authors: Schilp J. , Kuhn T. , Mahler G. 
Published: July 2007

AbstractA quantum kinetic analysis of the coupled carrier–LO‐phonon dynamics in photoexcited semiconductors is presented. The emission of phonons leads to the build‐up of a substantial nonequilibrium phonon distribution which is responsible for a reduced energy relaxation and an increased dephasing with increasing carrier density. Deviations from the semiclassical case are particularly pronounced at small phonon wave vectors, which cannot be reached by classical scattering processes. It turns out that the damping as introduced usually in quantum kinetic calculations leads to a violation of the conservation of the total energy.
Dephasing of acceptor bound excitons in II–VI semiconductors
Authors: Lummer B. , Heitz R. , Kutzer V. , Wagner J.‐M. , Hoffmann A. , Broser I. 
Published: July 2007

AbstractDegenerate four‐wave‐mixing experiments (DFWM) at the neutral acceptor bound exciton complex in CdS and ZnSe are reported. ps‐ as well as fs‐spectroscopy are carried out to investigate the dephasing processes at this complex. The results are discussed concerning scattering of free excitons, phonons, and interactions with impurity centers. Higher orders of diffraction in the DFWM process are modeled within the density matrix equations for noninteracting two‐level systems including propagation effects. From nonlinear quantum beat spectroscopy the binding energics of the acceptor bound biexciton in CdS and ZnSe are estimated.
A Green's function approach to the description of optical properties of disordered semiconductors
Authors: Stroucken T. , Anthony C. , Knorr A. , Thomas P. , Koch S. W. 
Published: July 2007

AbstractA Green's function approach to the optical response of disordered semiconductors is presented. The theory is illustrated studying light propagation in semiconductor multiple quantum wells with well‐width fluctuations and interface roughness. The combined influence of disorder, Coulomb, and propagation effects leads to characteristic features of the transmitted pulse.
Relaxation kinetics and photoluminescence lineshape of excitons in II–VI semiconductor quantum wells
Authors: Runge E. , Schülzgen A. , Henneberger F. , Zimmermann R. 
Published: July 2007

AbstractExciton localization by local potential fluctuations is studied theoretically and compared with energy‐ and time‐resolved photoluminescence experiments under resonant excitation for MBE grown ZnCdSe/ZnSe and ZnSe/ZnMnSe samples. Within the exciton lifetime of about 100 ps a narrowing of the luminescence band and a shift of the maximum position to lower energies is seen. This relaxation is described by a kinetic equation for particles moving independently in a spatially correlated disordered potential. The resulting exciton distribution at low temperatures has strongly nonthermal character. Good quantitative agreement with experimental data is found. An approximately linear temperature dependence of the radiative lifetime is expected theoretically. The photoluminescence of a 2 nm ZnCdSe quantum well shows, indeed, an increase of the exciton lifetime from 80 ps (at 5 K) to 160 ps (at 40 K).
On thermometer operation of ultrasmall tunnel junctions
Authors: Müler H.‐O. , Hädicke A. , Krech W. 
Published: July 2007

AbstractThe temperature dependence of the I–V characteristics of many single‐electron tunneling devices enables thermometer operation of these systems. Two normal conducting kinds of them are investigated, a) a single junction in a high‐impedance environment and b) a double junction. The characterstics of botu devices show a cross‐over from Coulomb blockade at low temperatures to ohmic behavior at high temperatures. The related differential conductivity dip allow the determination of the temperature of the junctions. Both configurations a) and b) are expected to work at least within the range 0.5 ≦ βEc ≦ 10, where EC the coulomb energy of the system under investigation. An analytical solution for both low‐and high‐temperature cases of a) and b) as well numerical results and their fit are presented, including the effect of co‐tunneling in case of a double junction.
Theoretical model of the density of states for random dilute binary alloys
Authors: Brezini A. , Bouamrane R. , Hamdache F. , Depolier C. 
Published: July 2007

AbstractA theoretical model of the density of states for random binary alloys is presented in the dilute limit based on a mean‐field approach. The model incorporates both diagonal and off‐diagonal disorder as well as short‐range order. Extensive results are reported for the density of states and various physical quantities in the limit of weak concentration and compared to other theories.
Periodic wave solution and its stability in antiferrornagnet Ni(C2H8N2)2NO2ClO,4
Authors: Liu Wu‐Ming , Wang Heng , Zhao Xiaopenc , Zhou Ben‐Lian 
Published: July 2007

AbstractIntroducing the coherent state ansatz and the time‐dependent variational principle, two partial differential equations of motion are obtained from the Hamiltonian. Employing the method of multiple scales, these equations are reduced into the envelope function equation and the amplitude function satisfying a nonlinear Schrödinger equation is found. The periodic wave solution and analysis of its stability in the antiferromagnet Ni(C2H8N2)2NO2ClO4 is derived.
Spatial correlation of laser‐generated electrons and holes in quantum wells
Authors: Belitsky V. I. , Cantarero A. , Pavlov S. T. , Cardona M. , Korovin L. I. , Lang I. G. 
Published: July 2007

AbstractThe spatial correlation of hot electrons and holes generated by light in a semiconductor quantum well (QW) is studied. For hot electron‐hole pairs in a polar material, this correlation is determined by the interaction with LO‐phonons. We analyze the distribution FN(r, K) of electrons and holes which are created in a given light absorption process, with respect to their relative separation r and total quasimomentum ħK, after the emission of a number N of LO‐phonons. The relationship between the spatial distribution of electrons and holes in these intermediate states and the cross‐section of multi‐phonon resonant Raman scattering (MPRRS) is established. Spatial correlation effects are strongly enhanced in low‐dimensional systems, a fact which is also reflected in the MPRRS efficiency.
Ginzburg‐Landau Equations and the Upper Critical Magnetic Field in Graphite Intercalation Compounds
Authors: Konsin P. 
Published: July 2007

AbstractThe Ginzburg‐Landau equations of a dirty two‐band superconductor, where superconductivity is driven by the interband electron‐phonon interaction are derived. On using these Ginzburg‐Landau equations, the obtained formulas for the critical field Hc2 describe well the temperature and angular dependences of Hc2 in graphite intercalation compounds (GICs). The calculated H∥ for C6K show a linear temperature dependence in a broad temperature range up to the values of the reduced temperature t = T /Tc ≈ 0.3 which is a general feature of GICs.
Low‐Temperature Anomalies in the CdI2Cd Crystalline System
Authors: Bolesta I. M. , Kityk I. V. , Filipecki J. , Zount H. 
Published: July 2007

AbstractFrom the measurements of elastic coefficients, piezooptical constants, and dilatometrical lengthening the existence of an improper ferroelastic phase transition of first order in the CdI2Cd single crystalline system within the temperature range 40 to 60 K is found. Different values of the temperature hysteresis are revealed for the piezooptical and elastic constants. From the data obtained an essential role of electron‐phonon interaction in the appearance of the mentioned phase transitions is concluded. The obtained results clearly show that in the CdI2Cd single crystalline system at lower temperatures long‐range forces appear between the impurity subsystems, which due to the specific electron‐phonon interactions tend to the appearance of the phase transitions. The behaviour of the elastic constants and the lengthening indicate the possible ferroelastic nature of these transitions. Simultaneously the existence of the temperature hysteresis reflects the first‐order nature of the mentioned transitions.
Magnetopolaron in a Cylindrical Quantum Wire
Authors: Pokatilov E. P. , Klimin S. N. , Balaban S. N. , Fomin V. M. 
Published: July 2007

AbstractThe dependence of the electron energy spectrum on a magnetic field is obtained for the case of a cylindrical quantum wire with an infinite interface barrier potential and a parabolic potential within the wire. The results are represented for the dependence of bulk‐like and interface phonon contributions to polaron energy levels on a magnetic field. The magnetopolaron resonance is considered and the splitting of polaron levels is found.
Correlation between the Porous Silicon Morphology and the Photoluminescence Efficiency
Authors: Goudeau P. , Naudon A. , Vezin V. , Halimaoui A. , Bomchil G. , Lambert B. 
Published: July 2007

AbstractSmall‐angle X‐ray scattering is applied to investigate the microstructure and the morphology of three photoluminescent porous silicon samples of the same porosity (80%) but prepared using different electrochemical treatments: (A) as‐prepared, (B) as‐prepared 65% porosity, followed by an oxidation treatment and an oxide dissolution in HF, (C) as‐prepared 65% porosity followed by a HF dissolution. Although the PL spectra are almost similar in energy, there are differences in their intensities: the luminescence intensity of the as‐prepared sample A is a bit greater than the one observed for sample B and much more greater than the one corresponding to sample C. If one assumes the same surface passivation (Si‐H) for the three samples then these differences in luminescence intensity may be due to the different PS morphologies which are evidenced in SAXS curves at low q values.
Saturation and Voltage Quenching of the Porous Silicon Luminescence and Importance of the Auger Effect
Authors: Romestain R. , Vial J. C. , Mihalcescu I. , Bsiesy A. 
Published: July 2007

AbstractTwo important observations for porous silicon, the saturation and the voltage selective quenching of the photoluminescence, are presented. Their similarities are pointed out and discussed in two phenomenological models, the saturation of the absorption and an Auger effect. The consequences of carrier accumulation in quantum crystallites are emphasized in both cases.
The effects of LO‐phonons to Electrons in Quantum Wires
Authors: Onwuagba B. N. , Wei Bao‐Hua 
Published: July 2007

AbstractThe microscopic model is used to describe the interaction between bulk‐like phonon modes and electrons in one‐dimensional (1D) quantum wires. The total transition rate for phonon modes and electrons in 1D quantum wires is discussed in the framework of the generalized 1D Fröhlich Hamiltonian. Numerical results are presented and compared with previously related work.
Conduction Band Edge Charge Densities in InxGa1−xSb
Authors: Bouarissa N. , Aourag H. 
Published: July 2007

AbstractThe empirical pseudopotential method coupled with the virtual crystal approximation which incorporates compositional disorder as an effective potential is used to compute the electronic conduction band edge charge densities at the Γ and X points for the ternary alloy InxGa1–xSb. It is found that these charge densities are strongly dependent upon the stochiometric coeficient x. Such differences are crucial for a comprehensive understanding of interstitial impurities and the response of specific band states to perturbation in ternary alloy semiconductors.
Magnetic Field Induced Polarization of Luminescence in Paramagnetic and Spin‐Glass Phases of Cd1–xMnxTe
Authors: Kusraev Yu. G. , Koudinov A. V. 
Published: July 2007

AbstractThe magnetic field induced polarization of photoluminescence is studied at different temperatures in Cd1–xMnxTe samples with x ranging from 0.005 to 0.38. The mechanism of polaron alignment is shown to depend on manganese content and temperature. In paramagnetic samples polarization is governed by thermal disorder of magnetic polaron axes, while in the spin‐glass phase the magnetic anisotropy of the lattice spin system predominates. The change of the mechanisms becomes visible when plotting polarization versus temperature.
Bragg‐Williams Model of Thermal Defect Formation in Ordering Binary Alloys with D03 Structure: Applications to Fe3Al
Authors: Spišák D. , Mehrer H. 
Published: July 2007

AbstractThermal defect formation in ordering binary alloys with DO3 structure is studied in the framework of a Bragg‐Williams model including nearest and next‐nearest neighbour bonds and applied to the case of Fe3AI. Values for vacancy concentrations on the various sublattices are deduced including the configurational entropy of the system but neglecting defect formation entropies. Vacancy concentrations are found to be fairly high especially on the Fe sublattices. Antisite atom concentrations are calculated and found to be several orders of magnitude higher than vacancy concentrations. Information about short‐range ordering is also achieved. Some consequences for diffusion in DO3 ordering alloys are discussed.
Compton Profile of Ruthenium
Authors: Kothari R. K. , Joshi K. B. , Sharma M. D. , Ahuja B. L. , Sharma B. K. 
Published: July 2007

AbstractThe first measurement of the Compton profile of polycrystalline ruthenium is reported and compared with recent APW calculations of Papanicolaou et al. with and without correlation effects. A comparison with our calculation based on the renormalised‐free‐atom (RFA) model is also made. It is seen that the incorporation of electron correlation effect improves slightly the agreement between APW theory and experiment but the best agreement is found for 4d7.65S0.4 configuration within the RFA model.
Electrical Study of 123 HTSC (77 to 400 K) with Varying Fraction of Y. Explanation of the Normal State Behaviour
Authors: Roy D. , Ghosh B. , Neogy C. , Deb S. K. , Nag A. 
Published: July 2007

AbstractBy varying the fraction n of yttrium in copper oxide based ceramic superconductors (nRE)BaCuO (RE = Y/Dy) it is found that below a certain n the dc percolation path through superconducting grains is lost and the material behaves insulator‐like with variable range hopping mode of electrical transport (In ϱ ∞ T−1/4. Experiments also show that the variation of resistivity ϱ with temperature T in the normal state for samples (n ≧ 0.25) exhibiting a superconducting transition is far from linear as the temperature is raised. By an extension of Mott's original ideas to polaron hopping with decreased localisation it is found that In ϱ should vary as T in satisfactory agreement with experiment. Thus, the so‐called “anomalous temperature variation of resistivity” in the metal‐like normal statc as well as in the insulator‐like state with increased disorder is explained within a single framework of hopping of localised carriers.
2D Scaling Properties of the Angular Dependence of the Critical Current Density in (YBa2Cu3O7)3/(PrBa2Cu3O7)8 Superlattice
Authors: Li K. , Qi Zh. 
Published: July 2007

AbstractThe critical current density Jc of the [(YBa2Cu307)3/(PrBa2Cu307)8 (YBCO)3/(PrBCO)8] superlattice as a function of the angle θ between the direction of the magnetic field and the c‐axis is measured in several magnetic fields at T = 55.8 K. Experimental results show that the angular dependence of Jc can be well scaled by a 2D model, i.e., only the perpendicular field component is relevant. The pinning mechanism in this film is discussed.
Theory of the Thermopower and Nernst Effect in Random Two‐Component Solid Systems
Authors: Fishchuk I. I. 
Published: July 2007

AbstractThe theory of the thermopower and the Nernst effect in inhomogeneous solid systems which consist of random high‐ and low‐conductivity regions is developed using the effective‐medium theory. An approximation is discussed in the case that the effective conductivity depends merely on the pair of conductivities in the components as this would happen in the absence of thermoelectricity. It is shown that this approximation can be used in the presence of thermoelectricity in almost all cases of random two‐component systems. It is found that the Nernst coefficient has the minimum value in the vicinity of the percolation threshold.
Carrier Relaxation in a‐Si:H/a‐Sic:H Multilayers Studied by Picosecond Transient Reflectometry
Authors: Galeckas A. , Petrauskas M. , Wang F. , Schwarz R. 
Published: July 2007

AbstractThe dynamics of photocarriers under high excitation in a series of a‐Si:H/a‐SiC:H multilayer structures with different bilayer thicknesses is studied with picosecond resolution using pump‐and‐probe reflectivity measurements. By varying both the photon energy and the intensity of the pump beam, the processes of carrier thermalization from extended into localized states on a picosecond time scale and free carrier trapping assisted processes on a nanosecond time scale are identified. The obtained relaxation time dependence on bilayer thickness is explained in terms of the competition of carrier scattering and enhanced recombination processes at the interfaces. The parallel and perpendicular transport peculiarities of photogenerated carriers are discussed.
The Off‐Center Effect on the Diffusion Coefficient of Cu+ and Li+ in the KCl Lattice
Authors: Despa F. 
Published: July 2007

AbstractIt is well‐known that the diffusion coefficients of the Cu+ cation in the NaCl and KCl lattices exceed by three or four orders of magnitude the corresponding self‐diffusion coefficients in the intrinsic temperature regions. This fast diffusion of the Cu+ has been explained in many papers as an interstitial diffusion although the optical spectra do not confirm the existence of interstitial Cu+. In this paper a new mechanism for fast diffusion is proposed. The model assumes that the equilibrium positions of the cationic impurities are noncentral and that the diffusion proceeds by hopping across the potential barrier along the nonlinear paths with the highest probability. The main result shows that the off‐center position considerably enhances the diffusion. Theoretical diffusion coefficients are obtained by modelling the potential barrier. Changes of the configuration entropy and the vibration spectra due to the presence of the noncentral impurity are included in the model. The numerical results of the diffusion coefficient computed in this way are in agreement with the experimental data and it is shown that if the impurity is placed close to the central site the due diffusion coefficient is close to that for the cationic self‐diffusion. The Li+ cation case is dealt with as the case of the Cu+ cation.