Table of contents

The authors experiments show that there are four, three, two and one hydrogen atoms involved in the defect complexes corresponding to the 2210 cm^-1, 2066 cm^-1, 1980 cm^-1 and 1832 cm^-1 infrared (IR) peaks, respectively, in the neutron-transmutation-doped floating-zone silicon (NTD FZ-Si) system. On the basis of the correlation of the thermostability and the oscillator frequency with the number of hydrogen atoms involved in these IR peaks, they attribute the 2210 cm^-1, 2066 cm^-1, 1980 cm^-1 and 1832 cm^-1 IR peaks to the vacancy+4H, vacancy+3H, vacancy+2H and vacancy+1H defect complexes, respectively. The mechanism of the formation of the vacancy+nH defect complexes in the NTD FZ-Si:H system has been discussed.

The reversible cubic to or from rhombodedral (O_h⁵ to or from _3v⁵) phase transition of GeTe-rich (GeTe)_1-x((Ag₂Te)_0.5333(Bi₂Te₃)_0.4667)_x solid solutions is studied by means of high-temperature X-ray analysis. The temperature and composition changes of the rhombohedral lattice parameters are found. They prove the displacive nature of the solid solution phase transition. With an increasing amount of heterovalent Ag and Bi atoms replacing Ge cations, the phase transition temperature T_c decreases.

The epitaxial growth of Ag on TiS₂(001) is characterized using reflection high-energy electron diffraction (RHEED), low-energy electron diffraction (LEED) and Auger electron spectroscopy (AES). Ag grows in the (111) orientation epitaxially on TiS₂(001) with Ag(110)//TiS₂(100). The growth mode belongs to the Volmer-Weber type, which means that Ag forms three-dimensional clusters on top of TiS₂(001). Ag also diffuses slowly into the substrate. The evolution of the electronic structure during this intercalation process is studied in detail with angle-resolved ultraviolet photoelectron spectroscopy (ARUPS) and X-ray photoelectron spectroscopy (XPS). The authors observed a striking difference between surface Ag and subsurface or intercalated Ag. They conclude that Ag atoms on TiS₂(001) have little interaction with the substrate, while upon intercalation charge transfer takes place from Ag to TiS₂. For comparison, they also studied Na and K at the TiS₂(001) surface. At low temperature (-140 degrees C), Na deposition results in an ordered ( square root 3* square root 3)R30 degrees superstructure. Na and K intercalation proceeds very rapidly. The Ti2p core-level spectra provide additional evidence that charge transfer has taken place after deposition and intercalation of Ag, Na and K.

This paper is devoted to the systematic study of questions concerning the use of spin-space groups (SSG) in calculation and qualitative analysis of the electronic states for crystals with spiral magnetic order. The types of operators that may enter into the symmetry group of a spiral are investigated. Introduction of the wavevector of an electronic state on the basis of the generalized Bloch theorem is discussed, and it is shown that the possibility of the choice of the wavevector is not unique. The condition imposed on the symmetry operations belonging to the group of a given Bloch vector and the formula describing the symmetry of eigenvalues in reciprocal space are obtained and appear to be substantially different from counterparts used in traditional cases of collinear and non-magnetic crystals. It is shown that, contrary to the traditional cases, there are spiral structures whose spectral symmetry is described by non-symmorphic space groups. The irreducible domain of reciprocal space is found for a number of concrete spiral structures. Methods of construction of the SSG double-valued irreducible representations and also of their basis functions are suggested. Special attention is devoted to the possibility of using the corresponding tables of ordinary space groups. In particular, it is shown that for spirals with hexagonal close-packed crystal structure the traditional tables may be used after minor corrections. The peculiarities of allowance for the operation of time inversion are discussed.

For pt.I see ibid., vol.3, p.8565 (1991). Compatibility relations between the electronic states of crystals with spiral magnetic order and the states of non-magnetic ferromagnetic and antiferromagnetic crystals are discussed. The results thus obtained permit one to predict the character of the electronic spectrum change on transition from a limiting case to a spiral structure. An anomaly in the optical characteristics of heavy rare-earth metals, which is observed on transition from the ferromagnetic structure to a spiral structure, is interpreted.

Pair and triple configurational interactions in Ni_1-cCu_c alloys are calculated by the LMTO-ASA-CPA method. Strong dependence of these interactions on concentration connected with the crossing of the d-band edge by the Fermi level is revealed. General microscopic expressions for these interactions are discussed for the case when the electron-electron interaction terms are taken into account in the framework of the density functional method.

Far infrared photoconductivity experiments have recently been reported on silicon-doped GaAs/GaAlAs multi-quantum well structures in magnetic fields of up to 8 T. The resulting spectra contain peaks which can be identified with transitions from the ground state to several higher excited states of a confined Si impurity. In this paper, details of a theoretical model are given which allow these transition energies to be predicted. The model is firstly used to determine transitions to states which are truly bound in the weak field limit. A set of hydrogen-like basis states is constructed in which the exponentials are expanded in terms of Gaussian-type functions in order to introduce some of the Landau-like behaviour required for large fields. Approximate eigenstates are then determined using a numerical diagonalization procedure. The possibility of transitions to states with m=2 is investigated, and mixing between basis states of different parity is allowed for in the case of impurities which are not located at the centre of a quantum well. These results are then used to determine the energies of so-called metastable state, which do not have a low-field counterpart. Transitions to these states are identified in the observed experimental data.

Deep-level transient spectroscopy has been employed to study the defect states in n-type CdTe crystals subjected to a variety of annealing treatments. By comparing the results from crystals grown by the Bridgman and travelling heater methods (starting from a common source of CdTe) and by considering the variation in properties with position along each boule, it was concluded that the electrical properties were strongly influenced by residual impurities in these materials. Eleven different defect states were detected with activation energies ranging from 0.2 eV to 0.86 eV. One of these was found only in In-doped samples and at least three were related to residual impurities and could be removed by annealing in liquid cadmium. Several defects were interpreted as complex centres involving native defects and impurities.

The authors numerically study the dynamics of a vortex line in type-II superconductors which is driven by vortex line tension, external driving force, pinning force and thermal fluctuations. Based on the local stochastic differential equation for the vortex motion, computer simulations are performed within the planar approximation (no torsion) to investigate the pinning time, which is the time for the vortex line to overcome the pinning centre.

The antiferromagnetic Heisenberg model with uniaxial anisotropy, arbitrary spin and dimension is solved approximately for D>0. The ground-state wavefunction, its energy, and zero-spin excitations are obtained. The validity range of the analytic approach is determined by comparing it with numerical computation and perturbative results in the large-D limit. It is shown that the paired, non-magnetic excitation method presented here yields more accurate results than linear spin-wave theory.

The concept of a Landau energy is used to calculate the energy of magnetic fluctuations. This is used to obtain fictitious magnetic fields akin to the Hellmann-Feynman forces used in phonon calculations. This generalized force method is applied to the spectrum of longitudinal magnetic fluctuations and specific numerical results are presented for Fe.

Local spin density functional theory is applied within the linearized muffin-tin orbital atomic sphere approximation (LMTO ASA) method to calculate the electronic structures of non-collinear antiferromagnets in FCC manganese and iron. Direct application of the theory leads to a Hamiltonian which is doubly degenerate for every band at every k-point. An irreducible representation is found which overcomes this problem. The total energies of single, double and triple spin density wave structures are found to be essentially indistinguishable within the limits of the calculation.

Nuclear relaxation arising from spin-spin interactions in the crystal unit cell is described by the model approach. The analytical expression for the free-precession signal (FPS) is obtained for an arbitrary velocity of the reciprocal spin flips. An excellent agreement with experimentally observed FPS in CaF₂ is obtained. The fundamental possibility to observe the critical slowing down of the phase relaxation in resonant magnetic fields is revealed.

Light scattering measurements are investigated as a function of temperature from 10 to 900 K in the tetragonal and cubic phases of a PbTiO₃ crystal. Phonon frequencies, ionic effective charges, spontaneous polarization and contribution to the dielectric permittivity are deduced from these data. The results show that the soft phonon and relaxation mode are both needed to describe the dynamics of this material.

The decay processes of metallic lanthanum after resonant 4d to 4f excitation by synchrotron radiation have been studied by means of electron spectroscopy. Excitation to the 4d⁹4f¹(³D₁) state, which is below the 4d ionization threshold, was found to decay predominantly through N_4,5O_2,3O_2,3 and N_4,5O_2,3V spectator resonance processes. The energy shift relative to the corresponding normal Auger energies was 1.6+or-0.3 eV in the case of NOO resonance Auger decay, whereas no energy shift was found for the NOV resonance Auger electrons. The excitation to the main 4d to 4f giant resonance was found to decay through autoionization leading to a one-hole final state 5s^-1 or 5p^-1, or through normal Auger processes. Autoionization processes are strong on the low energy side of the resonance, but when the excitation energy increases, normal Auger processes become more and more dominant, indicating a change in the nature of the giant resonance.

A formulation to evaluate equilibrium properties of a non-simple metallic liquid and plasma is presented in a unified fashion involving a neutral liquid as a special case; a multi-centre problem is to be solved in a coupled manner with a single-centre problem in this formulation. A liquid metal or a plasma is taken as a binary mixture of nuclei and electrons. Firstly, an inhomogeneous nucleus-electron mixture caused by fixing a nucleus at the origin is investigated by the density-functional theory for a single-centre problem to determine the internal electronic structure of an ion at the origin, which enables the authors to think of a liquid metal as an ion-electron mixture composed of ions with the same electronic structure as the central ion so built up at the origin. Thus, the radial distribution functions, a self-consistent potential for electrons and the ionic charge are obtained, if the bare ion-ion interaction is given beforehand; these quantities are used to solve the following multi-centre problem. Secondly, the problem of treating a homogeneous nucleus-electron mixture is reduced to the multicentre problem of an inhomogeneous electron gas under the external potential caused by randomly distributed nuclei. Thus, this system is shown to be regarded as a classical one-component fluid described by an effective Hamiltonian, with the same interparticle potential as the effective interionic interaction obtained in the previous single-centre problem; a bare ion-ion interaction is now created by an extension of the Gordon-Kim (GK) or tight-binding bond (TBB) model. This formulation offers a generalization of the GK and TBB methods to take account of the presence of the conduction electrons with use of self-consistent bound-state functions in a liquid. Here, a bound state is defined as a state with a negative eigenvalue or a resonant state with a long lifetime. The internal energy of a liquid metal is expressed in terms of output from the single-centre problem based on the nucleus-electron model.

The chemical and topological order of AgSi, AgGe and AlGe liquid alloys are investigated from the thermodynamic equations. On mixing, the component elements (Si, Ge, Al and Ag) undergo noticeable structural change. This suggests that AgSi is a segregating system, AlGe is chemically more ordered and AgGe undergoes inversion from order to segregation as a function of concentration.

Molecular dynamics computer simulations with shell-model potentials have been used to calculate the light scattering (Raman) spectra of molten LiCl. A significant improvement in the level of agreement with experiment is found over previous simulations with rigid-ion potentials. The improvement is attributed to the better description of the relaxation of the charge-density fluctuations in the shell-model simulations.

For original paper see ibid., vol.3, p.2595 to 96 (1991). Using standard Ewald summation, it is found that the energy of the three-dimensional Wigner crystal on the perovskite lattice is not lower than its energy on the BCC lattice. The BCC lattice remains the most stable known arrangement for the three-dimensional Wigner crystal.