bluuebunny/crossref_metadata_2025 huggingface dataset:
Adiabatic Method for Excitonic Molecules
Authors: Vukajlović F. R. , Vinitskii S. I.
Published: July 2007

The binding energy for excitonic molecules, four‐body systems with Coulomb interactions, is investigated using the adiabatic method usually applied to three‐body Coulomb systems. The infinite system of coupled Schrödinger‐type equations obtained, is approximated by a finite system of twenty‐one coupled equations and solved. The investigation gives an increase in binding of these systems practically in the whole region 0 < σ = me/mh ≦ 1, compared to previous varational results.
Quantum Theory of the Motion of a Quasi‐Particle in a Molecular Chain with Thermal Vibrations Taken into Account
Authors: Davydov A. S.
Published: July 2007

A quantum theory of collective excitations such as excitons and solitons in linear macromolecules is developed with thermal vibrations taken into account. Nonlocalized and autolocalized states are studied.
Dissociation and Thermodynamic Properties of Bipolarons
Authors: Li Yan‐Min , Chao K. A.
Published: July 2007

The degenerate perturbation theory is used to calculate the bipolaronic energy bands in various one‐, two‐, and three‐dimensional crystal structures. The dissociation energy of bipolaron is calculated, from which the stability of the bipolaron is investigated. Higher stability is found in lower‐dimensional systems. The triplet bipolaron state is almost as stable as the singlet bipolaron state, and so plays a very important role in determining the thermodynamic properties of bipolaronic systems.
Low‐Temperature Reflectivity Spectra of AgGaS2 and AgGaSe2 Compounds
Authors: Artus L. , Bertrand Y. , Ance C. , Lopez‐Soler A.
Published: July 2007

Reflectance measurements are made at 5 K on the ternary compounds AgGaS2 and AgGaSe2 in the energy range located above the fundamental gap of each compound up to 5.5 eV. Reflectivity spectra are interpreted according to a model previously proposed by the authors to interpret the reflectivity spectra of these compounds at room temperature in a wider energy range. According to this model, the reflectivity spectra of AgGaS2 and AgGaSe2 are found to be principally dominated by the existence of structures of type E1, E′0, E2, and E′1, as occuring in the binary analogues of zincblende type. Using this model, the structures are identified of Ei type which take place in the energy range in which the 5 K reflectivity spectra have been taken. Also, structures which may be due to pseudodirect transitions are observed.
Density of States and Photoconductivity of Hydrogenated Amorphous Silicon
Authors: Terekhov V. A. , Trostyanskii S. N. , Domashevskaya E. P. , Golikova O. A. , Mezdrogina M. M. , Sorokina K. L. , Kazanin M. M.
Published: July 2007

The results of the investigation of hydrogenated amorphous silicon films by ultrasoft X‐ray spectroscopy are compared with the measurements of photoconductivity on the same samples. It is shown that the saturation of amorphous silicon by hydrogen causes a decrease of the localized states density just above the valence band top which leads to the rise in photoconductivity. As a result, a maximum in the density of localized states clearly reveals itself at 1 eV above the top of the valence band providing n‐type conductivity.
An Unconventional Jahn‐Teller Phenomenon in a Valency‐Mixing Surrounding
Authors: Weber C. , Sigmund E. , Wagner M.
Published: July 2007

Stimulated by ESR measurements in SmB6:Er3+ the unusual g‐factor behaviour of the Er3+ ground state, which is extraordinarily isotropic, is ascribed to a new kind of Jahn‐Teller‐type phenomenon. The 4f–5d hybridization deformations of the Sm neighbourhood adopt the role which in conventional Jahn‐Teller systems is played by nuclear distortions. Arguments for this proposition and numerical results are given. These show that the “minimal” model constitutes a good starting point for refined theories. Several options of refinement are indicated.
Resonant Brillouin Scattering at Bound‐Exciton States in CdS
Authors: Gutowski J. , Schott J. , Broser I.
Published: July 2007

Strong resonant Brillouin scattering (RBS) is studied occurring under high excitation densities in the bound‐exciton energy range in CdS. RBS shows pronounced resonance enhancement not only at well‐known bound‐exciton ground state energies but also for energies of various excited states of these complexes. In this energy range, RBS has not been observed under low‐excitation‐density conditions. The phonon coupling determining the Stokes or anti‐Stokes shift of the RBS line maxima allows to calculate the spatial dimensions of the excited bound‐exciton levels acting as intermediate resonance states of the scattering process. In general, high‐density RBS spectroscopy is shown to yield important information on ground and excited states of bound exciton complexes.
Electron Spin–Lattice Relaxation in Fractals
Authors: Shrivastava K. N.
Published: July 2007

A theory of the spin–fracton interaction for paramagnetic ions in fractal structures is developed The interaction is exponentially damped by the self‐similarity length of the fractal and by the range dimensionality dphiv;. The relaxation time of the spin due to the absorption and emission of the fracton is calculated for a general dimensionality called the Raman dimensionality dR, which for the fractons differs from the Hausdorff (fractal) dimensionality, D, as well as from the Euclidean dimensionality, d. The exponent of the energy level separation in the relaxation rate varies with dRdphiv;/D. Also the spin relaxation rate due to a new type of Raman process is calculated in which one fracton is absorbed to affect a spin transition from one electronic level to another and later another fracton is emitted along with a spin transition such that the difference in the energies of the two fractons is equal to the electronic energy level separation. The temperature and the dimensionality dependence of such a process is found in several approximations. In one of the approximations where the van Vleck relaxation rate for a spin in a crystal is known to vary with temperature as T9, the calculated variation for fractals turns out to be T6.6 whereas the experimental value for Fe3+ in frozen solutions of myoglobin azide is T6.3. Since dR = 4/3 is used and the fracton range dimensionality dphiv; = D/1.8, it is expected to measure the dimensionalities of the problem by measuring the temperature dependence of the relaxation times. Also calculated is the shift of the paramagnetic resonance transition for a spin in a fractal for general dimensionalities.
Exact Solutions for Homogeneous Linear Biased Correlated Walks. A Case of the Boltzmann Entropy Decreasing in Time
Authors: Godoy S. V. , Fujita S. , Rodriguez R.
Published: July 2007

The probabilities of arrival with directions for a linear biased correlated walk satisfy a set of coupled linear difference equations. An exact analytic solution to the equations subject to a periodic‐boundary and homogeneous‐initial condition is obtained. The Boltzmann entropy (the negative of the Boltzmann constant kB times the Boltzmann H‐function) computed in terms of the solution may decrease (or increase) in time, depending on the chosen initial condition. The physical meaning of this striking behavior is discussed by taking diatomic impurities (CO) in liquid solution (Ar) under external electric fields. It is concluded that in the presence of a bias the sense of the time‐development of a general physical system cannot be given by the conventional Boltzmann H‐function.
Surface Phonon Polaritons in Semi‐Infinite Semiconductor Superlattices
Authors: Nkoma J. S.
Published: July 2007

Surface phonon polaritons in a semi‐infinite semiconductor superlattice bounded by vacuum are studied. The modes associated with the polaritons are obtained and used to obtain the dispersion relation. Numerical results show that polariton bands exist between the TO and LO phonon frequencies, and are found to approach two surface mode frequencies in the limit of large tangential wave vector. The dependency of frequencies on the ratio of layer thicknessses is shown. The results are illustrated by a GaAs—GaP superlattice bounded by vacuum.
A Contribution to the Theoretical Interpretation of the UPS Spectra of Monoatomic Adsorption of Oxygen on the Si (111) Surface
Authors: Karpushin A. A. , Sorokin A. N. , Semenova I. Yu. , Tomášek M.
Published: July 2007

A calculation is performed of the early stage of adsorption of atomary oxygen on the Si (111) surface in the on‐atom (top) position, saturating the dangling bond of the surface silicon atom. By considering the possible presence of a vacancy in the adsorbed oxygen monolayer, it is shown that the basic features of the experimental energy spectrum can be obtained without resorting to the idea of the existence of SiOSi bridge structures on the surface. Nevertheless, the results obtained do not contradict such an idea, nor the idea that the early stage of adsorption corresponds to a molecular form with a peroxide bridge formation. They merely suggest the possibility of an alternative early stage adsorption model. The method of calculation is the recently introduced generalized cluster Bethe‐lattice method.
The Electronic Heterogeneous States in Ferroelectric Semiconductors
Authors: Egorov B. V. , Egorova I. B. , Krivoglaz M. A.
Published: July 2007

The thermodynamically stable heterogeneous states (HS) are considered in ferroelectric semiconductors in which polarization and carrier concentration are self‐consistently dependent on the coordinates. These HS are shown to be thermodynamically favoured at carrier concentrations n being larger than the critical one and especially in a temperature range close to the Curie point of the second order phase transition. An investigation is made of the conditions for the formation of these HS, the phase diagram in variables T, n, and the characteristics: the values of periods (connected with the screennig length), the amplitudes of the carrier concentration and the polarization variations, and the coordinate dependence of the polarization. Depending on the parameters two types of the HS are possible: one with domains separated by sharp walls and the other with smooth wavelike polarization.
Energy Gap and Valence Band Structure of Cd1−zMnzTe1−ySey Alloys
Authors: Chehab S. F. , Woolley J. C.
Published: July 2007

Measurements of wavelength modulated reflectance are made as a function of temperature on Cd1−zMnzTe1−ySey alloys for both zinc blende and wurtzite fields. The room temperature energy gap E0 is found to show a square law variation with y independent of the change in crystal structure and the relation proposed by Moon et al. for E0 values at a general composition (z, y) is found to be satisfied. At low temperatures for the Cd1−zMnzSe alloys, the E0 values show an increase ΔE0 due to magnetic effects and the values of ΔE0 agree with the theoretical predictions of Alexander et al. Also for Cd1−zMnzSe, the values of valence band splittings are used to show that the fractional d‐like character of the valence band increases linearly with z and has a value of ∼0.26 at z = 0.2.
Recursive Scattered‐Wave Approach to the Electronic Density of States of Topologically Disordered Systems
Authors: Solbrig H.
Published: July 2007

The electronic density of states is calculated from the incident‐field amplitudes of a multiple scattering problem based on a muffin‐tin model. Using the idea of Haydock's LCAO recursion method, the multiple scattering between atomic angular‐momenturn channels is replaced by multiple scattering between incident‐field distributions of decreasing local relevance. The proposed method is tested numerically for a cluster of 13 nickel atoms.
The Influence of Carbon Vacancies and Local Atomic Displacements on the Electronic Structure of Niobium Carbides
Authors: Novikov D. L. , Ivanovskii A. L. , Gubanov V. A.
Published: July 2007

A nonempirical Xα discrete variational method is used to calculate clusters that with respect to the carbon sublattice simulate complete and nonstoichiometric niobium carbides. The presence of carbon vacancies is found to lead to the formation of an extra peak near the low energy edge of metallic band. A discussion is presented of the effect of niobium atom local displacements near the anion vacancies on electronic structure, chemical bond, and charge distribution in NbCx. Data obtained are compared with the results of X‐ray photoelectron spectroscopic studies of niobium carbides.
Quantum Theory of Thermopower in Quasi‐Two‐Dimensional Semiconductor Quantum Well Structures
Authors: Kubakaddi S. S. , Mulimani B. G. , Jali V. M.
Published: July 2007

A quantum‐mechanical theory for the thermopower in quasi‐two‐dimensional semiconductor quantum well structures, using the density matrix approach, is developed. Expressions for thermopower are obtained, both, when the temperature gradient is applied parallel and perpendicular to the plane of the layer forming the quantum well. The expressions obtained for the longitudinal configuration agree with those obtained from the conventional Boltzmann transport equation in relaxation time approximation.
Magnetic Order in Intermediate Valence Systems
Authors: Nolting W. , Ramakanth A.
Published: July 2007

A „hybridized”︁ s—f model is used in order to investigate the possibility of a coexistence of ferromagnetism and intermediate valence in systems which fluctuate between a magnetic and a nonmagnetic 4f configuration. The Curie temperature Tc, is determined, the local magnetic f‐moment mf, the valence nf and the static susceptibility χ as functions of the f‐level position Ef, the hybridization V, the s—f exchange g, and the Bloch bandwidth W for semiconducting as well as metallic 4f systems. It is found that electronic fluctuations destablize the local moments, but enhance the coupling between them. This leads to a Tc‐maximum just in the intermediate valence phase. Many results remarkably depend on, how the gap between the 4f‐level and the lower band edge (or Fermi‐edge) is closed, by a shift of the f‐level towards the conduction band (alloying!) or by a respective broadening of the band (external pressure!). Striking differences between semiconducting and metallic 4f‐systems are observed, while qualitatively similar behaviour is found for systems with ferromagnetic and systems with antiferro magnetic s—f exchange coupling. Magnetic phase diagrams in terms of Ef, W, V, and conduction band occupation n are derived and discussed. Qualitative agreement is found with recently performed experiments on systems like EuO, EuRh3B2, CeNixPt1−x, Ce(Rh1−xOsx)3B2,‥.
Continued‐Fraction Approximation for the Inverse Brillouin Function
Authors: Katriel J.
Published: July 2007

The first nine coefficients in the continued‐fraction representation of the inverse Brillouin function are obtained. The approximation thus generated is demonstrated to be of sufficient accuracy over the whole physically interesting range, in contrast with the corresponding power series. Possible applications of the inverse Brillouin function in non‐iterative molecular field theory as well as to the construction of the effective Hamiltonian, using the experimentally determined temperature dependence of the magnetization, are pointed out.
59Co NMR and Nuclear Magnetic Relaxation Study of the Magnetic Superconductor Y9Co7
Authors: Figiel H. , Barata A. C. , Guimarães A. P.
Published: July 2007

The magnetic superconductor Y9Co7 presents in its structure magnetic and non‐magnetic Co atoms. A search is made of the 59Co NMR lines attributed in the literature to magnetic Co atoms, with negative results. For the strong 59Co NMR line arising from nuclei of non‐magnetic Co atoms the relaxation times T1 and T2 versus temperature are measured directly at 6.5 and 9.0 MHz. A linear dependence on temperature is observed for 1/T1 which can be attributed to interactions with conduction electrons. 1/T2 is not linear with temperature, an effect that is related to the temperature dependence of the magnetization.
Short‐Time Behaviour of the Transverse Auto‐Correlation Function of the 1D XY‐Model
Authors: Farias G. A. , Gonçalves L. L.
Published: July 2007

The dynamics of the spin 1/2 one‐dimensional XY‐model in a transverse field is considered. The short‐time behaviour of the auto‐correlation function 〈S(t) S(0)〉 for the closed chain is obtained numerically by considering the exact results known for the open chain which are given in terms of Pfaffians. The bulk auto‐correlation is identified with the correlation 〈S(t) S(0)〉 for the open chain, and this identification is shown to be valid up to a characteristic time Jt ≅ 20. It is also shown, as expected, that the boundary effects are more pronounced for fields smaller than the exchange constant (h < |J|) and in the low temperature limit. The results are obtained for different temperatures and field strengths, and the numerical convergence is discussed in each case.
Raman and Infrared Spectra of YAsO4
Authors: Pradhan A. K. , Choudhary R. N. P. , Wanklyn B. M.
Published: July 2007

Single crystals and polycrystalline specimens of YAsO4 are prepared by flux method and solid‐state reaction, respectively. Crystal and powder Raman and infrared spectra at 300 K and crystal Raman spectrum at 77 K of YAsO4 are taken to study the internal and external vibrations of AsO4−3 ions. It is found that lattice vibrations with k = 0 associated with the tetrahedra of YAsO4 are similar to that of DyAsO4 and SmAsO4. The Raman spectrum at 77 K shows slight shifting of phonon lines to higher frequencies due to the decreasing anharmonic interactions of the vibrations. Similarly softening of one of the force constants (f4) at 77 K in comparison to that of 300 K was observed. Different dosages of X‐ray irradiation produces a very little effect to create defects in the YAsO4 crystals.
Static Structure Factor of Non‐Simple Liquid Metals Bi, Ga, Sb, and Sn
Authors: Zou Xian‐Wu , Jin Zhun‐Zhi , Shang Ya‐Jun
Published: July 2007

A simple theoretic expression for the static structure factor a(Q) of non‐simple liquid metals is presented, based on the hard sphere cluster model. This expression is a superposition of two Ash‐croft‐Lekner expressions with weight factors representing the atomic percentage of each type of clusters. The structure factors of liquid Bi, Ga, Sb, and Sn are computed. The calculated results are in good agreement with experiments over the entire range of momentum space.
Ionic Conductivity of Magnesium and Aluminium Doped Sodium Chloride Crystals
Authors: Deb S. K. , Bandyopadhyay S. , Neogy C. , Nag A.
Published: July 2007

The electrical conductivity of magnesium and aluminium doped sodium chloride crystals are measured at 1 kHz as a function of temperature from 275 to 730°C with the help of an ac bridge. The results show that, unlike divalent defects, the conductivity of aluminium doped crystals is lower than those values of the pure crystals in the extrinsic range, suggesting strong association between the aluminium ion and the created cation vacancies.
On the Determination of Interaction Parameters from Correlations in Binary Alloys
Authors: Maysenhölder W.
Published: July 2007

The determination of interaction parameters from correlation functions in binary alloys is discussed by means of high‐temperature expansions for the correlations. The inherent nonlinearity of this „inverse problem”︁ of statistical mechanics leading to non‐unique solutions is emphasized. The formulation includes pair and triplet interactions. Some results of a specific „inverse Monte Carlo calculation”︁ are criticized. The paper provides a collection of formulae, especially for probabilities and correlations, which should prove useful for clarifying the subject.
Vibrational Properties of Hydrogen in Proton‐Implanted Silicon
Authors: Tatarkiewicz J. , Winer K.
Published: July 2007

Some aspects of the infrared absorption spectra of crystalline silicon containing implanted hydrogen or deuterium are interpreted on the basis of simple atomic cluster calculations. It is shown that the vibrational properties of the implanted ions can be understood solely by taking into account the effect of the host silicon network on the local impurity vibrations.
Lattice Vibrational Contribution to the Bulk Properties of Si and Ge
Authors: Kagaya H.‐Matsuo , Shoji N. , Soma T.
Published: July 2007

The lattice vibrational contributions to the bulk properties of Si and Ge are studied in the dynamical treatment using higher‐order perturbation. The internal energy, Helmholtz free energy, thermal pressure from lattice vibrational term, and the temperature dependence of elastic constants are quantitatively obtained.
The Pair Correlation Function and Mott Transition in Two‐Component Fermi Systems
Authors: Schmidt M. , Röpke G.
Published: July 2007

Many particle theory is applied to describe the properties of nonideal two‐component Fermi systems as, e.g., the electron—hole plasma in highly excited semiconductors. Density corrections to thermodynamic properties as the equation of state and the pair correlation function are considered. Starting with a separable model potential the T‐matrix is calculated analytically. Two models for density dependent two particle properties (binding energy, scattering phase shifts) are compared, simulation by variable potential parameters without account for Pauli blocking and explicite inclusion of Pauli blocking. The continuity of thermodynamic functions if the system undergoes a Mott transition and the importance of Pauli blocking for the compensation of Bose singularities are discussed. The borderline for the onset of Bose condensation in the continuum of scattering states is presented.
γ‐Quantum Resonance Scattering in a Plane‐Parallel Isotropic Layer
Authors: Mkrtchyan A. R. , Gabrielyan R. G. , Martirossian A. H. , Grigoryan A. Sh.
Published: July 2007

The problem of non‐coherent γ‐quantum scattering is investigated in the medium taking the multiple scattering into account. Two models of the elementary process of scattering of the resonant γ‐quanta by the nuclei are discussed. It is shown that in case of large values of the quantum reemission probability or a large effective thickness, the problem cannot be limited only to the quantum single scattering approximation.
Magnetic Properties of the Ising Ferromagnet of Large Spin with Biquadratic Exchange Interaction and Uniaxial Anisotropy
Authors: Iwashita T. , Uryǔ N.
Published: July 2007

For an Ising ferromagnet with S = 5/2, the magnetization 〈Sz〉 and the Curie temperature TC are calculated using the pair model approximation. Assuming bilinear and biquadratic exchange interactions (J and J′) between nearest‐neighboring pair of spins and uniaxial single‐ionic anisotropy D for each spin, the behaviors of 〈Sz〉 and TC as functions of these exchange parameters and the uniaxial anisotropy parameter are investigated for an Ising ferromagnet on crystal lattices of various types.
Optical Properties of Al Films within and beyond the Effective‐Medium Approximation
Authors: Jungk G. , Schultze V.
Published: July 2007

The complex dielectric function of slightly differently prepared polycrystalline Al films is determined ellipsometrically for photon energies hω between 1 and 4 eV. The results can be explained by symmetrical and asymmetrical EMA for hω ≧ 1.8 eV through the incorporation of Al2O3. Below 1.8 eV significant discrepances occur due to resonantly enhanced electric fields in nonspherical Al grains surrounded by a dielectric.
The role of single collisions in the process of scattering and stopping of 200 to 400 keV protons in thin gold foils
Authors: Bednyakov A. A. , Iferov G. A. , Kadmenskii A. G. , Naumova N. M. , Zhukova Yu. N.
Published: July 2007

The trajectories of 200 to 400 keV protons in 5 to 18 nm thick gold foils are simulated by means of Monte‐Carlo calculations. The impact‐parameter distributions of ion–atomic collisions at different emission angles are obtained. The impact‐parameter distributions of the mean energy transfered to the atom at given emission angles are calculated. The angular dependence of the mean energy loss is also calculated. By fitting the latter with experiment the impact‐parameter dependence of the energy transfer in a single collision is obtained.
Interrelationship between higher‐order elastic constants and pressure derivatives of dielectric constants for ionic crystals
Authors: Srivastava G. M. S. , Sinha R. K. , Shanker J.
Published: July 2007

An interrelationship between the pressure derivatives constants and higher‐order elastic constants is investigated. Some useful relations connecting the first‐ and second‐order pressure derivatives of dielectric constants, third‐ and fourth‐order elastic constants, and bulk modulus and its pressure derivatives are obtained. A numerical application of these relations in the case of alkali halide crystals yields results which are found to be in good agreement with available experimental data. The utility of the mathematical expressions reported in the present work is demonstrated by calculating the pressure derivatives of dielectric constants.
GaAs–AlGaAs quantum well of compositional graded interface in the envelope function approximation
Authors: López‐Gondar J. , Rodriguez‐Coppola H. , Pérez‐Alvarez R.
Published: July 2007

Analytical expressions for the energy levels of a GaAs–AlGaAs quantum well with compositional graded interfaces are reported. The results for the first conduction and valence levels are compared with those obtained using a tight binding method. Good agreement between both the methods is obtained when the thickness of the graded layer is small enough. The method developed here can be straightforwardly extended to other structures of compositional graded layers. The results obtained for the energy levels when the well thickness is large and the layers of compositional graded material are small enough show that the usual abrupt interface approximation is valid to a great extent.
Dissipative effects of the interaction of crystal lattice surface with medium
Authors: Ya. Vetrov S. , Shabanov V. F.
Published: July 2007

The processes of dissipation due to the crystal interaction of lattice with medium are taken into account using the friction forces. The methods of discrete lattice dynamics shows that the dissipative forces induce surface waves of new type which penetrate deeper to crystal and damp weaker than the waves existing without dissipation. The possibilities to discover and use the obtained surface vibrations are considered. Besides it is shown, that the accounted dissipation leads to essential modification of known surface waves: their frequency and damping is renormed, penetration to crystal decreases, at intensive enough dissipation the surface waves become aperiodic surface motions of different types. The estimations of surface vibration damping are given for contacts of crystal with gas and liquid.
A study of the electronic structure of Fe1−xCox alloys by a polarized positron annihilation
Authors: Szuszkiewicz S.
Published: July 2007

The results from the angular correlation curves measured for Fe1–xCox ordered alloys with and without a magnetic field are presented. The average numbers of the 4s‐like and 3d‐like electrons per alloy atoms as well as the average numbers of the d‐like electrons in majority and minority spin bands are determined as function of Co concentration.
To the theory of two‐magnon absorption of light by surface collective excitations in the singlet–triplet ferromagnets
Authors: Seidov Yu. M. , Suleimanov A. M.
Published: July 2007

By the multi‐time Green's function method the light absorption by surface excitations in the singlet–triplet ferromagnets is investigated using the pseudospin formalism. The possibility of two‐magnon absorption of light on the surface of the singlet‐triplet ferromagnets is shown. It is estimated that the absorption of light by the surface of singlet–triplet ferromagnets is due to the simultaneous emission of two surface magnons in different branches of the spectrum of the singlet–triplet ferromagnets.
Energy levels of triply ionized praseodymium in BiLiF4 crystals
Authors: Schultheiss E. , Scharmann A. , Schwabe D.
Published: July 2007

The energy level scheme of Pr3+ in BiLiF4 is investigated by means of polarized absorption and emission spectroscopy on single crystal samples at various temperatures. Vibronic lines appearing in the spectra are identified according to the q = 0‐phonons of the host coupling to electronic levels.
Analysis of the electrical conduction in CdHgTe crystals
Authors: Dziuba Z.
Published: July 2007

The electrical conduction versus magnetic field in p‐like CdHgTe samples at 77 K is investigated by analysing the conductivity tensor components. The electrical conduction is mainly due to electrons in the conduction band and low‐mobility carriers in an impurity band. In the investigated samples CdxHg1–xTe with the composition x ≈ 0.17 the concentration of electrons in the conduction band is higher than the intrinsic one and in samples with the composition close to HgTe the concentration of electrons in the conduction band is equal to or lower than the intrinsic one. The model of a half‐filled impurity band situated close to the bottom of the conduction band is proposed to account for the concentration of electrons in the conduction band.
Modifications of the hopping conductivity due to long‐range coulomb interactions
Authors: Goedsche F.
Published: July 2007

The conductivity law derived by Efros and Shklovskii for variable‐range hopping (VRH) in the presence of long‐range Coulomb interaction is modified to take into account new numerical results for the density of single‐particle states (DOS) within the Coulomb gap. The characteristic temperatures appearing in this modified VRH law, including limiting temperatures for the applicability of VRH, are expressed in terms of DOS parameters, localization length and dielectric constant. The results are compared with experimental studies in crystalline and amorphous semiconductors.
Electronic properties of liquid SbSe and BiSe alloys
Authors: Satow T. , Uemura O. , Matsumoto K. , Okamura S.
Published: July 2007

The electrical conductivity (σ), the magnetic susceptibility (χ), and the thermoelectric power (S) of liquid SbSe and BiSe alloys are measured as function of composition in the temperature range from the melting point to about 1000 °C. On adding Se to Sb and Bi σ indicates a rapid fall and χ has a sharp maximum of diamagnetism at the stoichiometric composition of M2Se3 in both the systems. A reversion of the sign of S is observed around the composition of Sb2Se3 in liquid SbSe alloys, while S in liquid BiSe alloys remains negative over a wide composition range including Bi2Se3. The calculated value of g (the ratio of real and free electron density of states at the Fermi level) using the observed values of σ begins to decrease in the vicinity of 50 at% Se and drops sharply at the concentration of 60 at% Se in both systems. Electronic properties obtained are discussed in the light of current transport theories employed in liquid semiconductors.
Many‐body effects in antiferromagnetic 4f‐systems
Authors: Bulk G. , Nolting W.
Published: July 2007

A many body approach is presented for the electronic excitation spectrum of an antiferromagnetic semiconductor with ABAB‐sublattice structure. By use of the s–f model the sensitive dependencies of the quasiparticle density of states (Q‐DOS) on the temperature T, the carrier concentration n, and the effective coupling constant g/W is derived and discussed. The electronic spin polarization per sublattice is a direct consequence of this Q‐DOS‐behaviour. It increases for higher band occupations, lower temperatures and stronger couplings g/W. The lower edge of the quasi‐particle spectrum shifts with increasing n to higher energies showing for fixed n rather small blue shifts as function of decreasing temperature.
Material constants of composites. I. General theory for the dielectric constant
Authors: Monecke J.
Published: July 2007

The classical problem of the determination of an effective dielectric constant for composites is reconsidered. It is shown that the usually applied effective medium approach of Bruggeman violates a fundamental requirement, called additivity in this work. A new expression is proposed, which does not show this deficiency.
Dynamics of phonon‐assisted optical interband processes in semiconductors
Authors: Stahl A. , Frank D.
Published: July 2007

The influence of the electron–phonon interaction on the dynamics of the electronic band edge is studied within the framework of the recently developed coherent wave approach. The applications being considered are the dynamics of an indirect band‐to‐band transition and the dissipative influence of spontaneous lattice vibrations on polariton propagation. The relation to the theory of spontaneous and induced light scattering is established.
Temperature dependence of the elastic constants for solids of cubic symmetry.Application to Germanium and Silicon
Authors: Toupance N.
Published: July 2007

The extension of the finite strain expansion of the Mie‐Grüneisen equation (taking into account the elastic constants in the reference configuration up to the fourth‐order) is used to derive the temperature dependence of the volumetric compression and of the second‐order elastic adiabatic moduli of cubic solids. Numerical results are given for germanium and silicon and compared to experimental data. Finally, the second pressure derivative of these constants is estimated at zero pressure and 300 K.
The exact solution of the real square‐lattice‐gas system
Authors: Szász A.
Published: July 2007

The square‐lattice‐gas model is calculated exactly by a special process. This model previously had no exact solution because it requires a general solution of the square‐lattice‐Ising model with external magnetic field, which also to‐date does not have an exact solution. In the present calculation an exact solution to the square‐lattice‐model is obtained in a form that does not require the solution of the external field contained in the Ising model.
The 7,7′, 8,8′‐tetracyano‐p‐quinodimethanide salt of the N‐n propyl quinoxalinium cation — its structure, conductivity, and triplet spin excitons
Authors: Firlej L. , Graja A. , Rajchel A. , Woźniak K. , Krygowski T. M.
Published: July 2007

A new organic semiconductor (N‐n propyl quinoxalinium)+ (7,7′,8,8′‐tetracyano‐p‐quinodimethanide)2− is synthesized and characterized by elemental analysis and X‐ray diffraction. The electrical dc conductivity, the thermoelectric power as well as the ESR spectra are reported and discussed. The crystal is of triclinic symmetry. TCNQ moieties stack plane‐to‐plane, in stoichiometric groups of four; adjacent columns from sheets interleaved by the cations. The charge transport properties are discussed in terms of a one‐electron semiconductor model with low temperature behaviour controlled by electrically active impurities. The ESR spectra are interpreted by the model of Q 1‐D mobile triplet excitons; it is consistent with the charge localization found by bond lengths analysis and assumed by the model of the electrical transport.
A semi‐empirical approach to the bulk properties of copper
Authors: Craig B. I. , Smith P. V.
Published: July 2007

A semi‐empirical method suitable for d‐band metals is presented. This method is an extension of the Chadi scheme which has been successfully applied to semiconducting systems. In this scheme the electronic structure is determined by the Slater‐Koster matrix method. For metals careful attention has to be now given to the dependence of the diagonal matrix elements upon the neighbouring atomic positions. The new method is applied to the calculation of several properties of copper, such as the bulk modulus, elastic constants and phonon frequencies, and shown to produce good agreement with the experimental values.
Analyticity breaking of wave functions and fractal phase diagram for simple incommensurate systems
Authors: Schellnhuber H. J. , Urbschat H.
Published: July 2007

The Aubry‐André transition for certain one‐dimensional quasiperiodic Schrödinger operators is discussed in terms of analyticity breaking for the states of the underlying periodic diamagnetic Ersatz‐Hamiltonian. The general concept is compared with recent developments in the theory cf non‐integrable Hamiltonian dynamics and illustrated by explicit calculations for the Harper model. It is shown that the latter is not structurally stable within the family of incommensurate systems derived from Bloch dynamics in irrational magnetic fields: A very simple non‐self‐dual quasiperiodic model is presented, which lies in the Harper universality class regarding critical behaviour but exhibits cascades of localization–delocalization transitions. The system has a “devil's fork” phase diagram, where localized and extended regions are separated by a fractal curve.
Physical properties of the TCNQ salts with 1‐methyl‐3‐alkylimidazolium derivatives
Authors: Nešpůrek S. , Koropecký I. , Šorm M. , Graja A. , Sopa E.
Published: July 2007

Electrical conductivity and spectral properties (UV–VIS absorption and temperature dependence of IR absorption) are studied in the series of 1‐methyl‐3‐alkylimidazolium (MRI+) 7,7′,88′–tetracyano‐p‐quinodimethanes \documentclass{article}\pagestyle{empty}\begin{document}$ {\rm (TCNQ)}^{\mathop {\rm - }\limits_{\rm .} } $\end{document} in the form of simple and complex salts. The poor electrical conductivity of simple salts (10−4 to 10−7 Sm−1) is influenced by the dimer arrangement of \documentclass{article}\pagestyle{empty}\begin{document}$ {\rm TCNQ}^{\mathop {\rm - }\limits_{\rm .} } $\end{document} stacks. The magnitude of the gap energy Eg, (between 1.0 and 1.2 eV) depends on the size of the donor. Combining these salts with neutral TCNQ0 molecules gives complex salts with electrical conductivities increased by 3 to 7 orders of magnitude. Eg decreases to 0.4 to 0.5 eV, which is in a good agreement with 0.4 eV obtained from IR measurements. The electrical conductivities of 1‐methyl‐3‐propylimidazolium (MPI), 1‐methyl‐3‐butylimidazolium (MBI), and poly‐(1‐methyl‐3‐allylimidazolium) (MPaI) complex TCNQ salts are also influenced by the donor level located about 0.05 to 0.06 eV below the conduction band.
Phase transitions in ordered and disordered ferrimagnets. I. Correlated molecular field theory and Monte Carlo simulations
Authors: Fähnle M. , Haug M.
Published: July 2007

The uniform and the staggered paramagnetic zero‐field susceptibility χ of ordered and disordered ferrimagnets are calculated by means of the correlated molecular field theory and by Monte‐Carlo computer simulations. The results are similar to the case of disordered ferromagnets: site disorder gives rise to a wide transition regime from the asymptotic critical behaviour to the mean‐field behaviour, with strong upward curvature of the plot χ−1(T). In contrast, bond disorder has only a weak influence on χ−1(T). For the ordered S = 1/2 / 1 Ising ferrimagnet on a simple cubic lattice the Monte Carlo simulation yields a critical temperature consistent with that found by high‐temperature series expansons of Schofield and Bowers.
Infrared properties of TeEA(TCNQ)2
Authors: Železný V. , Petzelt J. , Swietlik R.
Published: July 2007

Polarized reflectivity from three faces of TeEA(TCNQ)2 single crystals is measured in the frequency range 50 to 13500 cm−1 at room temperature. The spectra polarized closely to the TCNQ dimer axis are analyzed by means of Kramers‐Kronig relations to obtain the optical constants. They are also fitted to a model which has been previously applied to dimerized TCNQ salts. The model consists of an infrared active electronic oscillator (charge‐transfer mode) linearly coupled to the totally symmetric vibrations of TCNQ molecules. From the fit the microscopic electron–phonon coupling constants, transfer integral for the π‐molecular orbital t = 1864 cm−1, and the energy gap Δ = 938 cm−1 are evaluated. The most striking feature in comparison with other TCNQ salts is the low vibrational‐mode damping which leads to a very sharp and strong peak structure in the reflectivity and conductivity spectra.
Sensitized luminescence of pure and doped NaNO2 single crystals. I. Stationary spectra
Authors: Lisse F. , Köhlre J. , Pufahl H. , Schmid D.
Published: July 2007

The fluorescence and phosphorescence spectra of pure NaNO2 and of NaNO2 doped with KNO2 (up to about 2 × 10−3 mol KNO2/mol NaNO2) are investigated. Compared to the fluorescence spectra of pure crystals ten progressions of impurity‐induced lines are identified in the spectra of the doped crystals. The origin and the generating frequencies of these progressions are determined carefully, as well as the temperature and concentration dependence of their relative intensities with respect to those observed in pure crystals. A comparison of the shapes of impurity‐induced and unperturbed lines shows a striking difference: The unperturbed “zero‐phonon” lines (electronic transitions into intraionic vibrational levels of the NO2− without participation of interionic phonons) exhibit a pronounced asymmetry. The impurity‐induced lines, as well as the lines which are due to isotopically substituted NO2− are considerably narrower and Lorentzian shaped. A discussion of these observations will be presented in Part II.
Low‐temperature behaviour of the lithium modes in monoclinic Li2SO4
Authors: Cazzanelli E. , Fontana A. , Rocca F. , Frech R.
Published: July 2007

Polarized Raman spectra of anhydrous monocrystalline lithium sulfate are studied from 90 K to room temperature. The analyzed frequency range, between 260 and 580 cm−1, includes the lattice modes of the Li+ cations and the internal bending of the sulfate anions. The observed temperature dependence of the frequency, linewidth, and intensity of the Raman peaks can be explained by a weak phase transition around 180 K.
Microscopic Models for Substitutional OH− and CN− Defects in Alkali‐Halide Crystals
Authors: Dick B. G.
Published: July 2007

Microscopic models for substitutional OH− and CN− defect ions in NaCl structure alkali‐halide crystals are used to calculate the preferred orientations, electric dipole moments, and tunneling matrix elements of these defects in various host crystals. Both Coulomb and short range interactions are included. The pressure induced transition of OH− in KI from preferred 〈110〉 to 〈100〉 orientations can be plausibly accounted for with the model. Vibration frequencies for translational motion of the defect predicted by the model are too high to be used to explain observed low lying excitations in the 10 to 30 cm−1 range.
Corrections from Electron‐Electron Interaction to the One‐Particle Density of States in Strongly Anisotropic Two‐Dimensional Systems
Authors: Firsov Yu. A. , Nakhmebov E. P. , Prigodin V. N. , Weller W.
Published: July 2007

A simple model is proposed for the description of the one‐particle density of states ν(ε) of the degenerate electron gas in the grain boundary (inversion layer) of a semiconductor bicrystal or in a surface superlattice. The electron–electron interaction effect is calculated renormalized by scattering on the disorder in diffusion approximation. In the case of small tilt angles, where the grain boundary may be considered as a planar array of edge dislocation tubes (chains), a crossing‐over is obtained for ν(ε) from one‐dimensional (∼1/|ε|1/2) to two‐dimensional (∼ In2|ε|) behaviour in the neighbourhood of εcross ∼ w⟂2|ε|/h. Here ε is the difference of the energy from the Fermi energy, τ is the relaxation time due to scattering on the disorder, w⟂ is the transverse overlap integral characterizing the strength of the electron tunneling between dislocation tubes.
Correlation and Influence of Phonons in Calculations of the Density of States in Thin Films
Authors: Kierul J. , Stasiak J. W. , Kluczynski M.
Published: July 2007

The density of electronic states and its spatial distribution in thin films, based on the original adaptation of the coherent‐potential approximation (CPA) (Wojtczak and others) is obtained by including the phonon–electron interactions in the form proposed by Chen et al. This new approach allows to derive the line shape for electronic levels in which the broadening is also connected with lattice vibrations. The detailed calculations are performed for 4s copper and nickel thin films with f.c.c. lattice and (100) crystallographic orientations of the surfaces. The lattice vibrations are taken in pseudoharmonic approximation.
Dynamical Screening, Collective Excitations, and Electron‐Phonon Interaction in Heterostructures and Semiconductor Quantum Wells. Application to Double Heterostructures
Authors: Wendler L. , Pechstedt R.
Published: July 2007

The collective excitations of a double heterostructure are examined in detail. Including the important effects of the interfaces of the system the uncoupled modes are analysed, which are the long‐wave optical interface phonon modes, LO phonon modes, and intra‐ and intersubband plasmon modes. The electron‐phonon interaction is discussed and the coupling functions are calculated and discussed in graphical form. The resulting coupled modes, intra‐ and intersubband plasmon‐phonon modes, are calculated for different approximations of the polarization function, the random‐phase approximation, the plasmon‐pol approximation, and the long‐wave approximation. The dispersion curves of these modes are presented in graphical form for various cases. It is shown that the Landau damping of the modes strongly depends on the layer thickness and the concentration of the quasi‐two‐dimensional electron gas.
On the Theory of “Deep” Electronic Impurity States in Many‐Valley Semiconductors
Authors: Savvinykh S. K.
Published: July 2007

For many‐valley semiconductors a theory of electron states localized on short‐range point defects, i.e. defects with action ranges of the order of the lattice constant, is developed. Resonance electron scattering near the bottom of conduction band and a small value of the bound energy of the localized state are assumed. The transition from the general multiband formulation of the problem to the zero‐range potential approximation is accomplished. For crystals placed in crossed electric and magnetic fields the general expressions are derived determining the energy spectrum and wave functions of localized states.
On Trigger Properties of Molecular Organizates. II. Switch Waves in Donor‐Acceptor Systems with Strong Electron‐Deformation Interaction
Authors: Gaididei Yu. B. , Yakimenko I. I.
Published: July 2007

The charge transport is studied in the case of multilayer organizates consisting of donor and acceptor monolayers separated by dielectric molecular layers. It is shown that in such systems the charge can propagate as switch (trigger) waves. The velocities of these waves are calculated and their profiles are investigated as well.
Correlated Molecular Field Theory for the Ferromagnetic Regime of Amorphous Systems
Authors: Holey T. , Fähnle M.
Published: July 2007

Using the modified equation of state of Arrott and Noakes a self‐consistent correlated molecular field theory for the ferromagnetic temperature range of amorphous systems is developed. The temperature dependence of the spontaneous magnetization and of the width of Mössbauer lines is calculated, as well as the Arrott‐plots of amorphous ferromagnets.
To Applicability of Hamilton's Equations in Quantum Many‐Body Problems
Authors: Lindner U.
Published: July 2007

The connection between Schrödinger equation and Hamilton equations for interacting many‐particle systems is given and it is shown in which way the Hamilton function has to be constructed. Starting from an identity for the Hamilton function a criterion is derived which permits to check approximations. Applying this criterion to former calculations to the soliton problem in a modified Hubbard chain the consistency of the used approximation is shown.