[en] The windforce acting upon a host atom and the impurities Ta, Cr, and Ni in niobium is calculated in a finite cluster model. In this model all strong and multiple scattering effects up to l/sub max/ = 2 are preserved. Special attention is given to the influence of the vacancy, the cluster size, and of charge transfer. A positive windforce is found, in accordance with experiment, so that this appears to be not directly related to a hole current contribution, contrary to what is believed commonly. (author)

[en] In this paper values of the extremal caliper dimensions of the Fermi surface of indium as determined from the r.f. size effect are presented. Four of these caliper dimensions are used in a KKRZ scheme to calculate the Fermi surface. The calculated Fermi surface dimensions are in agreement with the experimental results within the experimental error of 1%. (author)

[en] The Takahashi-Tachiki equations, describing the critical properties of proximity effect systems in the dirty limit, are solved exactly using the full eigenfunction expansion. Both parallel and perpendicular critical fields are calculated. The theory is applied to experimental data of Kanoda et al. for V/Ag and of Chun et al. for Nb/Cu, using the T_c of the superconducting material and the diffusion coefficients of both materials as fit parameters. For the 3D systems the fits compare nicely with the experimental results, but for 2D systems this is not always the case. It is found that the V and Nb critical temperatures necessary to fit the data can be larger than the corresponding bulk critical temperatures. This contrasts with what has been observed for single V and Nb films. Additionally, the diffusion coefficients resulting from the fit procedure are found to be much smaller than one would expect from resistivity measurements. In the light of these anomalies earlier less complete calculations are reconsidered. It turns out that several assertions are superficial and cannot be affirmed by the results of the present work

[en] The Takahashi-Tachiki proximity-effect theory is applied to the Nb/Ta multilayer system. The diffusion coefficients of the two metals and the critical temperature of Nb are used as free parameters in fitting experimental phase diagrams. Magnetic-coherence-length scaling is used in order to obtain phase diagrams that best reproduce the measured data. Several parameter sets can compete in fitting an experimental curve. It is not always possible to decide which set gives the most realistic result. (author)

[en] An improved description of the critical properties of metallic multilayers is obtained by introducing the concept of a scaled magnetic coherence length in the Takahashi-Tachiki theory. By that, the absolute magnitude of the upper critical fields and the position of the dimensional crossover are uncoupled and become independent quantities. Much better phase diagrams can be obtained by using this scaling procedure. Although this concept is inspired by the character of disagreement between the theory without scaling and experiment, the procedure lacks an external justification. The fact that it works might serve as an indication how the Takahashi-Tachiki theory has to be modified in order to give a realistic quantitative description of upper critical fields in real metallic multilayers. The theory is applied to the V/Cu, V/Ag, Nb/Cu, and Nb/Ag systems. copyright 1996 The American Physical Society

[en] The quasiparticle local density of states (LDOS) is studied in clean normal-metal endash superconductor (NS) and superconductor endash normal-metal endash superconductor (SNS) junctions with increasing transverse size, from quasi-one-dimensional to three-dimensional. It is shown that finite transverse dimensions are related to pronounced effects in the LDOS, such as fast oscillations superimposed on the quasiparticle interference oscillations (for NS) and additional peaks in the bound state spectrum in the subgap region (for SNS). Also, the validity of the Andreev approximation is discussed. It turns out to be an acceptable approximation in all situations tested. copyright 1996 The American Physical Society

[en] An exact expression is derived for the matrix Green's function of a clean superconducting layered structure with an arbitrary number of interfaces. A multiple-scattering approach is employed, in which the interfaces act as the scattering centres. Some initial applications of the theory to systems with transverse dimensions which vary from narrow to wide are given. The local density of states is calculated for an SNS and for an SNSNS junction ('S' standing for a superconducting layer and 'N' for a normal layer). For certain critical transverse widths the exact theory shows remarkable features not seen in the Andreev approximation. If the gap function for the systems is calculated self-consistently it turns out that for transverse dimensions smaller than twenty per cent of the superconducting coherence length, superconductivity is suppressed. (author)

[en] The present understanding of the magnitude of the direct force on hydrogen and its isotopes deuterium and tritium is discussed in the light of new experimental data and existing theoretical formulations. By this it is proven, that the direct valence of hydrogen can be significantly different from the unscreened jellium value of unity. Furthermore, a more detailed interpretation of a resistivity dependent direct valence is given, which clarifies the controversy around that subject. Selfconsistent calculations of the electronic charge density at and around an interstitial, at all positions along its electromigration jump path, are required to come to a more complete understanding of the measured results. (orig.)

[en] We present results for the local density of states in the superconducting (S) and normal metallic (N) layers of an SN multilayer, and the supercurrent, based on a Green function formalism, as an extension of previous calculations on NS, SNS and SNSNS systems. The gap function is determined self-consistently. Our systems are chosen to have a finite transverse width. We focus on phenomena which occur at so-called critical transverse widths, at which a new transverse mode is starting to contribute. It appears that for an arbitrary width the Andreev approximation (AA), which takes into account only Andreev reflection at the SN interfaces, works well. We show that at a critical width the AA breaks down. An exact treatment is required, which also considers ordinary reflections. In addition, we study the influence of an interface barrier on the coupling between the S layers

[en] The Korringa-Kohn-Rostoker (KKR) Green function extended-defect formalism, used to describe the scattering of Bloch electrons in a dilute alloy, is generalised to include an asymmetric defect centred on a lattice site. The revised theory is then used to investigate conduction electron scattering from Frenkel pairs in Cu. Such defects consist of two self-interstitial atoms centred on a vacant lattice site forming a dumb-bell oriented along the <100> axis. The generalised formalism allows one to calculate the cluster t matrix T for the Frenkel pair cluster including the surrounding displaced nearest neighbours. It was found that the interstitials at the vacant lattice site could still be treated within the muffin-tin potential as a central scatterer characterised by a t matrix which is non-diagonal in the angular momentum. Electron scattering rates and Dingle temperatures are calculated and discussed in view of preliminary experimental results. (author)