bluuebunny/crossref_metadata_2025_split huggingface dataset:
Dynamics of Carrier Hopping in Exponential Band Tails of Quasi‐One‐Dimensional Systems in Electric Field
Authors: Singh M. , Tarutani Y. , Takagi K. 
Published: July 2007

AbstractThe dynamics of carrier hopping in band tails of a quasi‐one‐dimensional (QOD) system is studied in the presence of temperature and electic field. A method is used in which it is assumed that localized states are distributed randomly in both space and energy coordinates and the hopping of carriers occurs in both coordinates. The exponential form of the density of states for band tails is considered. The hopping rate and the time dependent demarcation energy are calculated in the activated and nonactivated relaxation regimes. The hopping rate varies with the electric field as (1  β2)−1/γ and exp [(1  β2)] for the AR and the NAR regions, respectively. Here β and γ are directly proportional to the electric field and the temperature, respectively. Numerical calculations are performed for the hopping rate and the demarcation energy as a function of β and γ for both regions.
Oscillation Phenomena on the Magnetoresistance of the Organic Superconductor K‐(BEDT‐TTF)2I3
Authors: Helm P. , Kraak W. , Schweitzer D. , Keller H. J. 
Published: July 2007

AbstractHigh‐field magnetotransport properties of single crystal samples of the quasi‐two‐dimensional organic compound K‐(BEDT‐TTF)2I3 are investigated at low temperatures in magnetic fields up to 12 T. Pronounced quantum oscillations of the magnetoresistance (Shubnikov‐de Haas effect) are observed in magnetic fields above 8 T. In the magnetic field orientation perpendicular to the high conducting b−c plane four different SdH oscillations with fundamental fields 570, 2710, 3280, and 3850 T are detected. The corresponding extremal areas of the cross sections of the Fermi surface are found to be in good agreement with theoretical band structure calculations. For the first time “giant” angular oscillations of the magnetoresistivity are observed in K‐(BEDT‐TTF)2I3. These oscillations are periodic in tan θ in agreement with the quasi‐classical explanation by Yamaji. From the experimental data the electronic parameter π/akF ≈ 0.58 can be estimated.
Longitudinal and Transverse Random‐Field Ising Model with Arbitrary Spin (S)
Authors: Wang Yong‐Qiang , Li Zhen‐Ya 
Published: July 2007

AbstractThe Ising model with transverse and longitudinal random fields, which have trimodal and bimodal distribution, respectively, for arbitrary spin (S), is investigated by combining the pair approximation with the discretized path integral representation (DPIR). The phase diagrams for S = 1, 1.5, and 2 are obtained, where some fascinating phenomena are observed.
Early Stages of Pore Formation on Si During Etching in HF Solutions
Authors: Zur Mühlen E. , Niehus H. 
Published: July 2007

AbstractThe fabrication of porous silicon (PS) with controlled pore size distributions is of importance for reproducible manufacturing as well as it may help to elucidate the origin of light emission from this material. The pore formation on p‐doped Si(111) surfaces is studied. For this purpose hydrogen passivated surfaces are prepared by wet chemical treatment. After introduction into UHV system a 1 × 1 LEED pattern is readily obtained without any further treatment. These surfaces are etched at the open circuit potential (OCP) in HF solutions with pH‐values ranging from 1 to 10. Atomic force microscopy is used to characterize the dependence of pore formation on time and acidity. It is found that narrow pore size distributions can be obtained when HF solutions with high pH‐values are used.
Radiative and Nonradiative Recombination in Porous Silicon. What Can We Learn from Spin Resonance?
Authors: Stutzmann M. , Brandt M. S. 
Published: July 2007

AbstractRecent results of spin‐resonance investigations of porous silicon are presented. Special attention is given to nonradiative and radiative recombination processes as detected by spin‐dependent recombination (spin‐dependent photoconductivity, SDPC, and optically detected magnetic resonance, ODMR). Pb‐like defects are identified as the main recombination centers which quench both photoconductivity and visible photoluminescence in porous Si. Strongly localized triplet excitons are found as the initial states of visible luminescence.
Efficient Visible‐Light Emission from Si/CaF2 (111) Heterostructures Grown by Molecular Beam Epitaxy
Authors: Vervoort L. , Bassani F. , Mihalcescu I. , Vial J. C. , d'Avitaya F. Arnaud 
Published: July 2007

AbstractThe elaboration by molecular beam epitaxy of a new luminescing Si‐based material is presented, i.e. small grain polycrystalline Si/CaF2 multi‐quantum wells. The static luminescence properties are studied as a function of Si layer thickness, and the time dependent luminescence features as a function of wavelength and temperature. There is a rather striking similarity with the photoluminescence of porous Si, both in spectral position as in decay dynamics. The disappearance of the luminescence when the Si layers become too thick, and the blue‐shift of the spectra when the Si layer thickness decreases, favour the quantum confinement hypothesis for the origin of the light emission. The important role of oxygen as passivating agent after ageing in air, is also pointed out.
New Hydrogen‐Localized Vibrational Modes in Proton‐Implanted GaAs Activated by γ‐Ray Irradiation
Authors: Wang L. P. , Zhu W. X. , Qin G. G. 
Published: July 2007

AbstractTwo new hydrogen‐localized vibrational modes (LVMs) in proton‐implanted GaAs activated by γ‐ray irradiation are observed at 1726 and 1688 cm−1 (295 K), and at 1771 and 1702 cm−1 (4.2 K) in infrared absorption spectra, respectively. The integrated absorption intensities of both bands increase with increasing γ‐ray radiation dose. A tentative structural model for the new hydrogen LVMs is suggested.
Phonon‐Assisted Two‐Photon Absorption in the Reststrahl Region of Excitons in Alkali Halides
Authors: Fröhlich D. , Rübenacke St. , Schlutt Ch. , Stolz H. 
Published: July 2007

AbstractThe two‐photon spectrum of RbI is investigated in the energy region of the lowest IS exciton. A significant increase of the two‐photon signal is observed when crossing the transverse energy and scanning through the excitonic reststrahl region. This phenomenon is explained by a LO‐phononassisted absorption process based on the Fröhlich exciton‐phonon coupling. Evaluating the two‐photon excitation within a two‐band model allows a quantitative analysis, which shows good agreement with the experimental data. Besides a scaling factor, the only fit parameter is the exciton Bohr radius that is found in reasonable agreement with the Wannier exciton model.
On the Problem of the Existence of Davydov Solitons
Authors: Todorović D. , Ristovski Lj. , Tošić B. S. 
Published: July 2007

AbstractDavydov's soliton model, which introduces autolocalised excitations in a soft molecular chain, is applied also for explaining the energy transport process in the α‐helix protein being considered as a system consisting of three coupled molecular chains (spines). However, there is an inconsistency in the consideration of the single chain case compared to the case of coupled chains (α‐helix). Namely, in the Hamiltonian of the single molecular chain some relevant exciton‐photon terms are omitted which are, on the other hand, included in the Hamiltonian of the coupled chains. Our numerical analysis shows that the omitted term can have a very important influence on the soliton properties in Davydov's model.
Quasicluster Electronic Structure Calculations of Point Defects in Crystals
Authors: Titov S. A. 
Published: July 2007

AbstractAn earlier proposed quasicluster embedding scheme is applied to the calculations of the ground state potential surfaces, energies, and probabilities of electronic transitions in neutral and charged point defects in KCI, SiO2, and diamond crystals. The model is closely related to the periodic supercell approach (providing similar electronic structure characteristics) and the molecular cluster one. Two modified versions of the model are proposed, which improve results of calculations of ground state properties (especially for small quasiclusters) and transition energies. Ground state potential surfaces calculated for defects in ionic and semiionic crystals are better than those obtained using supercell and molecular cluster models.
Magnetic Susceptibility of the Anderson Lattice with Finite f‐Band Width
Authors: Panwar S. , Singh I. 
Published: July 2007

AbstractAn extension of the periodic Anderson model by considering the finite f‐band width is considered. A variational method is used to study the temperature dependence of the valence nf and of the magnetic susceptibility χs for various values of f‐band width. As the f‐band width is reduced, the low temperature peak in the susceptibility χs gets sharpened.
Two‐Photon Excitation to the High‐Lying Triplet State of F Color Centers in LiF Crystals
Authors: Ter‐Mikirtychev V. V. , Tsuboi T. 
Published: July 2007

AbstractThe excitation spectrum for the anti‐Stokes luminescence band with a peak at 538 nm, which arises from the electronic transition of the singlet excited state 1E to the ground state 1A2 in F+3 centers of LiF crystals, is obtained for the first time using the first harmonic radiation of a tunable Al2O3:Ti3+ laser. From the quadratic dependence of the luminescence intcnsity on the average pumping power, the luminescence is understood to be caused by two‐photon excitation from the ground state 1A1 to the triplet state 3A2. The peak of the two‐photon excitation band was determined to be located at 24331 cm−1 from the 1A1 ground state.
Temperature Dependence of Core and Valence Thermal Vibrations in Germanium
Authors: Jeyakanthan J. , Saravanan R. , Mohanlal S. K. 
Published: July 2007

AbstractAn X‐ray analysis is made for the core and valence thermal vibrations in germanium, using powder X‐ray intensity data collected at various temperatures (298, 573, and 733 K). The overall thermal vibration is split into the components of core and valence thermal vibrations, because the valence electrons oscillate with different phase and amplitude than the core electrons due to bond polarizability. The data collected at the above temperatures are analyzed using locally developed computer programs. In the first phase, the overall Debye‐Waller factors are estimated. Then in the second phase, the core and valence contributions of the thermal vibrations are refined. The error in the fitting procedure is found to be less than 2%, and in the third phase an attempt is made to refine the individual anharmonic thermal parameters (βcore and βval), which result in unrealistic thermal parameter values. Hence only the overall anharmonic thermal parameters are evaluated and the results are reported.
Numerical Study of One‐Dimensional Strongly Correlated Systems
Authors: Kumari K. , Singh I. 
Published: July 2007

AbstractThe path‐integral formulation along with the quantum Monte Carlo method is used to study the physical properties of the one‐dimensional Hubbard model for various band fillings and values of interaction strength U. Results for singlet and triplet pairing correlations, local square magnetic moment, total energy, probability of double occupancy, and nearest‐neighbour charge‐density correlations are presented. These results are explored at β (inverse temperature) = 2.0, 1.0, and 0.5 for the linear chain N = 16. These results show that the effect of correlation on the physical quantities is small for low band‐filling and it becomes most evident for the half‐filled band at finite temperatures.
The Renormalization of the Energetical Spectrum and the Peculiarities of High Density Paraexciton Luminescence Band
Authors: Bobrysheva A. I. , Moskalenko S. A. , Shmiglyuk M. I. , Russu S. S. 
Published: July 2007

AbstractThe renormalization of the energetical spectrum of paraexcitons in the presence of a Bose‐Einstein condensate (BEC) of orthoexcitons or at least of their saturation is studied. Due to the conversion of a pair of orthoexcitons into a pair of paraexcitons an absolute instability in the energy spectrum of paraexcitons appears. The appeared paraexcitons can be downscattered by optical phonons T5 (88 cm−1) into a state above the bottom of the paraexciton band. This can be the reason of the observed peculiarities in the paraexciton luminescence band. On this basis a new explanation of the appearance of an extra peak in the luminescence spectrum of the uniaxially stressed Cu2O crystal is suggested. It has the same origin as the bump of the luminescence band in unstrained crystals. The spectral positions of the extra peak and of the bump differ due to the diminution of the ortho‐para splitting in uniaxially stressed crystals. The difference of their widths is due to different densities of the condensed orthoexcitons in stressed and unstrained crystals.
Surface Barrier at the Edge of a Uniaxial Anisotropic Type‐II Superconductor
Authors: Saif A. G. , El‐Sabagh M. A. 
Published: July 2007

AbstractThe structure of the surface barrier, using the uniaxial anisotropic London equation, for a high‐temperature type‐II supcrconducting quarter‐space, is studied. The role of a transport current on the annihilation of the surface barrier is investigated. It is found that this barrier depends on the external field strength, the value of the transport current flowing through the sample, and the orientation of the external field. It is shown that the results obtained will reduce to some known results in some limiting case.
Superconductivity and Structural Transition in Mo‐Stabilised R1–xCaxSr2Cu3Oy Compounds (R = Pr, Nd, and Y)
Authors: Zhao Y. , Zhang Y. L. , Choi C. H. , Chen B. , Kennedy H. , Sorrell C. C. 
Published: July 2007

AbstractSr‐based 123 compounds R1–xCaxSr2Cu2.7Mo0.3Oy with R = Pr, Nd, and Y are successfully stabilised by partial substitution of Mo for Cu. A tetragonal‐orthorhomic‐tetragonal transition is observed for R = Y and Nd, which is induced by different oxygen content in the samples. Tc of the samples is sensitive to the oxygen content other than the structure. For Pr‐contained samples the resistivity decreases systematically with increasing the Ca dopant and oxygen content. The results show that the hybridisation of the conduction electrons with the 4f band of Pr in Sr‐based 123 compounds is weaker than that in Ba‐based 123 compounds.
Thermoelectric Power of Solid Solutions (PbTe)1–x(Bi2Te3)x with 0 ≦ x ≦ 0.02
Authors: Christakudi T. A. , Christakudis G. Ch. , Borissova L. D. 
Published: July 2007

AbstractThe thermoelectric power (Seebeck coefficient) S which is one of the parameters determining the figure of merit Z of thermoelectric materials is measured for polycrystalline (PbTe)1 ‐x(Bi2Te3)x solid solutions as a function of temperature T (in the interval from 80 to 350 K) and composition x (in the range 0 ≦ x ≦ 0.02). The experimental results are analyzed on the basis of the two‐band nonparabolic Kane model and the transport coefficient theory of AIVBVVI semiconductors. Some information on the phonon‐drag term in this coefficient is specially extracted from the data.
The Temperature Dependences of the Magnetization and the Quadrupolar Moment for the Spin‐1 Ising Model
Authors: Tóth L. 
Published: July 2007

AbstractThe temperature dependence of the magnetization and the quadrupolar moment is studied for the spin‐1 Ising model on a honeycomb lattice in one‐spin cluster approximation. Nearest‐neighbour ferromagnetic exchange interactions J with concentration p and exchange interactions αJ (|α|≦1) with concentration (1 − p ) are considered.
Phase Transition of a Ferromagnetic Ising Superlattice in a Transverse Field
Authors: Wu Yinzhong , Zhong Jialin 
Published: July 2007

AbstractUsing the effective‐field theory with corrections, the critical behavior of a magnetic superlattice consisting of two different ferromagnets is examined in a spin‐1 transverse Ising model. The dependence of the critical temperature on the thickness of the constituents in a unit cell is investigated for different cases. A critical value of the interface exchange coupling (Jab)c above which the interface magnetism appears is found, and the effect of the transvcrsc field on (Jab)c is also investigated. All the results are understandable by phase diagrams.
On the Theory of Diffusion in Amorphous Metals
Authors: Davydov L. N. , Spolnik Z. A. 
Published: July 2007

AbstractDiffusion in solids with random activation energy of individual jumps is analyzed. The experimentally observed relation between the activation energies of diffusion for metal glasses and for the corresponding crystals is explained under reasonable assumptions. The activation energy is shown to be not the most probable buth rather close to the minimum allowed (by the percolation mechanism) activation energy of individual jumps. For an interstitial solute the activation energy parametrically depends on the mean solute concentration. The expression for the diffusion coefficient is obtained. The short‐range diffusion is also considered.
Relativistic Positronium Planar Channeling. Ground State Properties
Authors: Boev O. V. 
Published: July 2007

AbstractThe ground state of a relativistic positronium (Ps) atom moving in the planar channeling regime in a Si crystal is investigated within the continuum potential approximation. The strong dependence of the internal structure of the Ps atom and its spatial distribution inside the crystal is found to be a function of the total energy of Ps. The squeezing of the atom and destroying of the spherical symmetry of the Ps ground state in a crystal with increasing Ps total energy is demonstrated. A brief discussion of applications and extensions is given.
Lattice Dynamics of Superionic Cerium Dioxide
Authors: Sinha M. M. , Ashdhir P. , Gupta H. C. , Tripathi B. B. 
Published: July 2007

AbstractA modified rigid ion model is used to investigate the lattice dynamics of the superionic cerium dioxide compound with an appropriate effective charge in the electrostatic interaction and third‐neighbour interaction for the short‐range forces. The present model is more physical than others in predicting the phonon frequencies in superionic compounds.
On the Dielectric Constants of AIBIIIC Chalcopyrite Semiconductor Compounds
Authors: Márquez R. , Rincón C. 
Published: July 2007

AbstractValues of the static, ϵ0, and high‐frequency, ϵ∞, dielectric constants of I‐III‐VI2 chalcopyrite compounds are estimated by using an empirical model proposed by Nag for cubic semiconductors, which relates these constants to the average atomic number of its constituent atoms Zav. It is found, as in the cubic semiconductors, that the inverse of both these constants is linearly related to Zav. It is also suggested that ϵ0 and ϵ∞ thus obtained should be more reliable than those calculated from the energy gap Eg, due to the wide range of values of this parameter reported in some I‐III‐VI2 chalcopyrite compounds.
Thermal Expansion and Compression of Alkaline Earth Oxides and Cesium Halides at High Temperature and High Pressure
Authors: Upadhyay S. P. , Kumar M. 
Published: July 2007

AbstractTemperature and pressure dependence of thermal expansion and compression of alkaline earth oxides and cesium halides with NaCl‐ and CsCl‐type structures is investigated. The theory of interionic potentials based on the quantum mechanical form of the overlap repulsive energy is used to investigate the interatomic separations as a function of temperature and pressure from room temperature up to the melting temperature and from zero pressure up to the structural transition pressure. The values of van der Waals dipole‐dipole and dipole‐quadrupole energies are also included in the model. The results are used to predict the temperature and pressure dependence of the coefficient of volume thermal expansion using a formula derived on the basis of the thermodynamic analysis. The results are compared with available experimental data and discussed in the light of recent research.
Correlations between the Szigeti Charge and the Differences in Phase Volumes in the Alkali Halides
Authors: Koh A. K. 
Published: July 2007

AbstractCorrelations between the Szigeti charge and the difference in phase volume in the alkali halides are presented. It is shown that the lattice bonding is enhanced if an alkali halide shows a bigger fractional change in volume at melting. The fractional change in volume for RbF can be obtained by extrapolation.
Polarons in a Cylindrical Quantum Wire with Finite‐Barrier Well
Authors: Pokatilov E. P. , Klimin S. N. , Balaban S. N. , Fomin V. M. 
Published: July 2007

AbstractThe eigenfunctions and eigenenergies of an electron in a finite‐barrier cylindrical quantum wire are obtained. The case of different electron band masses in the cylinder and the barrier material is discussed. The polaron binding energy and the polaron effective mass due to the interaction of an electron with two cylindrical‐interface optical modes as well as with cylindrical bulk‐in and cylindrical bulk‐out confined LO‐phonon modes are calculated, and their dependence on the radius of the cylinder is studied in detail. The comparison with the results for a 2D polaron is performed.
Study of the Electronic Structure and the Role of Gallium 3d Electrons in Gallium Nitride
Authors: Jhi S.‐H. , Ihm J. 
Published: July 2007

AbstractAb‐initio pseudopotential total energy calculations are performed for gallium nitride in both wurtzite and zincblende structures. The 3d electrons of gallium are treated as valence states and the behavior of the 3d electrons and their influence on higher‐lying valence states are investigated. It is found that the explicit treatment of the gallium 3d electrons as interacting valence states rather than inert core states systematically improves various structural and electronic properties.
Impurity Binding Energy of a Cylindrical Quantum Wire in a Magnetic Field
Authors: Xiao Zhigang , Zhu Jiqian , He Fenglai 
Published: July 2007

AbstractBy using the strong‐perturbation theory, suitable trial wave functions are chosen and the ground‐state energy and the binding energy of the ground state of a hydrogenic donor in a quantum wire are calculated in the presence of a uniform magnetic field applied parallel to the wire axis. The quantum wire is assumed to be a cylinder of GaAs having an infinite confining potential. The ground‐state energy and the binding energy increase as the strength of the magnetic field increases. Our results agree with those of previous calculations. The calculating method is novel and has general significance.
Persistent Currents in Finite‐Width Mesoscopic Rings. The Role of the Interchannel Coupling and of the Electron‐Electron Interaction
Authors: Wendler L. , Fomin V. M. 
Published: July 2007

AbstractThe persistent currents of few interacting electrons with spin in mesoscopic rings are calculated in the ballistic regime. The energy bands of the finite‐width multi‐channel ring are calculated with the transfer‐matrix method including the interchannel coupling induced by the impurity scattering, and the electron—electron interaction. It is shown that in the case of a narrow‐width ring the electron—electron interaction and the confining potential build a rotating Wigner crystal of the few electrons, where the relative angular motions are harmonic oscillations if the impurity potential is weak. As long as this picture remains valid, the persistent current is not influenced by the electron—electron interaction. It is shown that the width of the mesoscopic ring is the critical parameter for the influence of the electron—electron interaction on the persistent current. With increasing width of the mesoscopic ring, the electron—electron interaction decreases the amplitude of the persistent current at low temperatures and increases it at higher temperatures. Further, for a finite width of the mesoscopic ring the interchannel coupling becomes important, which results in the occurrence of higher harmonics in the persistent current.