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It is already known that for a quantum system of independent boson or fermion quasiparticles, calculations can be performed explicitly in only one part if the remainder is replaced by an energy-dependent embedding potential. Using path-integral methods, the author extends this result to the case when arbitrary many-body interactions are permitted in the region where explicit calculation is to take place, provided that certain averaging (such as is involved in taking thermal expectation values), is carried out over the configurations of the other region. This result can be used to calculate the electronic structure and equilibrium atomic positions around defect structures where many-body effects are important locally. It is not necessary to solve the problem of the remaining part of the crystal in the absence of the local region; it is sufficient to know the solution in the perfect crystal. The author compares the embedding potential to Feynman's 'influence functional' approach and uses it to derive the well known scaling law for the Anderson model of a magnetic impurity.

For pt.I see J. Phys. C, vol.21, p.1953 (1988). The present paper is concerned with the problem of the polaronic states of positively charged particles in crystals. In contrast to the commonly considered case of electronic polarons such particles tend to reside on the interstitial sites of the crystal. To work out the consequences of this fact the interstitial-polaron model is investigated. This model is a slight modification of Holstein's molecular-crystal model treated in part I of this series. Using the variational approach introduced in part I of a new class of polaronic states appears to become stable in some parameter region in addition to the various types of states existing for the molecular-crystal model. These states will be called two-site states since they describe a particle effectively tunnelling between two neighbouring sites. They are shown to be increasingly important if a configuration dependence of the transfer integral is taken into account. The two-site states may be considered as a one-dimensional analogue of the 4T states which have been proposed for hydrogen and its isotopes in BCC metals.

The authors have evaluated the upper and lower bounds to the lattice relaxation energy gained on the self-trapping of excitons, using experimental values of transition energies for free and self-trapped excitons and theoretical values for lattice relaxation energies and optical transition energies. The lattice relaxation energy upon self-trapping of an exciton in alkali halides proves to be appreciably larger than that of a self-trapped hole. They discuss the implications for a number of solid state processes including the production mechanism of F and H centres and the desorption of halogen atoms following valence electron excitation.

Theoretical solutions have been derived for the galvanomagnetic transport properties of double- and multiple-layer continuous metallic thin films. Interface scattering as well as external surface scattering of conduction electrons have been taken into account when solving for the electron distribution function in the presence of a transverse magnetic field. The electrical conductivities and the Hall coefficients of thin films are also given.

The authors have examined seven reasonable asymmetrical dimer configurations for a Si(100) surface using the CNDO method. In this work, all structures resulting from higher-order dimer reconstruction are named according to Pauling and Herman's terminology. Reconstructed 4*1 and 4*2 surfaces are found to be energetically more favourable, followed by 2*2A and 2*1. The total energies per dimer of these four structures are reasonably close to each other and a disordered mixture of them might appear at the Si(100) surface. The results agree well with previous theoretical work as well as with experimental results. However, the 4*1 configuration cannot be confirmed as it has not been observed experimentally. The results on the amount of charge transfer to the dimer atoms and the dimer lengths for each configurations are also presented.

The theory of phonon-drag thermopower S_g is given for a quasi-1D electron gas in a GaAs heterostructure. The coupling of the electrons to 3D phonons is considered through acoustic deformation potential and piezoelectric fields. An expression for S_g is given which may be used for quasi-1D wires of different geometries. Numerical results are presented for both the screened and the unscreened value of S_g for cylindrical wires in the temperature range 1-10 K. For temperatures T>or=2 K the major contribution to S_g comes from the deformation potential scattering but for T<2 K the contribution to S_g due to piezoelectric scattering is significant. Screening reduces S_g by 40%. S_g increases as the density of electrons decreases and curves of S_g/T³ against T show maxima. The overall behaviour is dominated by the 3D character of the phonon system and is similar to that found previously for a quasi-2D electron gas coupled to 3D phonons.

A first-principles theory of the zero-temperature magnetocrystalline anisotropy in metals is discussed. It is based on a relativistic spin-polarised multiple-scattering theory. The magnetic moment can point along any direction with respect to the crystal lattice and the total energy is calculated. The difference between total energies for two different moment directions is the magnetocrystalline anisotropy energy. The authors show that this energy difference can be written as the difference in single-particle energies for the same charge density. The theory is illustrated with a calculation of the anisotropy in energy and spin contribution to the magnetic moment in nickel. It is found that the theory gives good qualitative agreement with experiment in this case. Numerical difficulties involved in the calculation are discussed.

The theory of Brillouin scattering of dielectric layered elastic media is formulated in a way that also treats the electromagnetic field quantum mechanically. The general expression for the cross section obtained by this approach is applied to the investigation of shear horizontal modes in the Brillouin spectrum of finite and semi-infinite dielectric superlattices.

The thermal conductivity lambda and the heat capacity rho c_p per unit volume of solid LiBr and RbF have been measured over the temperature T range 100-400 K and at pressures p up to 2 Gpa, using the transient hot-wire method. The results are compared with recent theoretical calculations. A predicted drop of lambda (T) below T^-1 dependence is observed for LiBr.

The pressure dependence of the magnetisation of Y₂Fe₁₇, Y₆Fe₂₃ and YFe₂ at 4.2 K has been deduced from forced volume magnetostriction measurements in fields up to 12 T. The pressure dependence of the ⁸⁹Y hyperfine field in the above compounds and YFe₃ has been measured using NMR. The results are consistent with a model in which a moment of approximately=-0.4 mu _B exists at the Y site of all four compounds as found in computer calculations for YFe₂.

CoSi₂/Si(111) interfaces have been prepared by annealing of a UHV-evaporated, Co layer at 500, 600, and 900 degrees C. Using electron microscopy at atomic-scale resolution, the authors have compared experimental pictures with an extensive set of calculated images. Their observations support Si-Si interfacial bonds consistent with a seven-fold coordination of the first Co layer. This is the first evidence of this interface geometry for CoSi₂, other reports being in favour of Co-Si bonds and a five-fold or eight-fold Co coordination.

The authors have undertaken a detailed theoretical investigation of the meta-magnetic transition in UCoAl. Using the fixed spin moment method in their calculations they can account for the observed meta-magnetic transition and find that the magnetic properties of UCoAl are dominated by a moment located on the uranium atom. This uranium moment is found to consist of an orbital moment that is larger and anti-parallel to the spin moment. The spin and orbital moments were calculated using the local spin-density approximation and the recently reported formalism for orbital polarisation together with the spin-orbit interaction.

The influence of a very intense electromagnetic wave (EMW) on the penetration of a static electric field into a two-dimensional electron gas (2DEG) is considered. A static field is created by a charge distribution in the plane parallel to the 2DEG; the electric wavevector is parallel to the same plane. The distribution of the DC part of the potential behind the plane of the 2DEG is calculated for the two simplest cases, the sinusoidal charge distribution and the point charge. In the first case the amplitude of the sinusoidal potential is found to be an oscillating function of the wave amplitude. With increasing EMW intensity the 2DEG becomes 'electrically transparent', i.e. stops screening the static field and giving a contribution to the image potential.

The energy and oscillation frequency of a single vortex line or soliton in a long Josephson junction with a spatially modulated Josephson penetration depth are calculated systematically. The resulting critical magnetic field H_c1, and the stability and pinning of the different soliton solutions are discussed. The pinning forces are strongest if the period length of the modulation is about three times larger than the average penetration depth (or coherence length) of the junction, although the absolute barrier height against free vortex movement still increases.

It is found that the 1115 and 1157 cm^-1 absorption bands in GaAs doped intentionally with ¹³C (measured at 300 K) are manifestations of the localised vibrational mode two-phonon absorption of ¹²C_As and ¹³C_As. The ratios of the absorption intensity for single-phonon processes to that for two-phonon processes for ¹²C and ¹³C in GaAs are about 87 at 300 K and 75 at 10 K, respectively.

The authors have analysed the cathodoluminescence spectra from single-crystal diamonds grown by the decomposition of a methane-hydrogen mixture in a microwave plasma. Crystals grown using methane concentrations of <or approximately=1% exhibit 'edge emission' at around 5.3 eV due to the recombination of free excitons in association with momentum-conserving phonons. When the CH₄ concentration is increased to 2% the edge emission becomes relatively weak, implying a degradation of crystal quality. All the diamonds exhibit bright blue luminescence in the visible spectral region due to donor-acceptor pair recombination. An emission line at 2.985 eV may be the N3 zero-phonon line which is commonly observed in natural diamonds; other emission lines are unique to these diamonds prepared by chemical vapour deposition. The widths of the zero-phonon lines suggest that the material is heavily strained.