J. Friedel

Electronic structure of primary solid solutions in metals

(1954). Electronic structure of primary solid solutions in metals. Advances in Physics: Vol. 3, No. 12, pp. 446-507.

NATURE OF THE DRIVING FORCE IN FLUX CREEP PHENOMENA

A more accurate expression for the driving force acting on Abrikosov vortex lines in hard superconductors is derived and used to calculate critical currents in Nb/sub 3/Sn containing cavities. (D.C.W.)

The high-Tc superconductors: a conservative view

Classical BCS superconductive couplings leading to small Tc‘s rely on phonon mediated weak coupling of delocalized electrons in three dimensional structures. Attempts to produce or explain higher Tc have considered the breakdown of one or several of these hypotheses. The possible role of quasilowdimensionality for delocalized electrons will be stressed, and the potential superiority of fine mesh three dimensional networks of chain conductors argued from that point of view.

On the Nature of the Magnetic Couplings in Transitional Metals

This paper suggests a simple model of magnetism for transitional metals which is somewhat intermediate between Heisenbergs atomic model and Stoners band model. Starting with a paramagneticd band, described in the tight-binding approximation and with equal population of both spin directions, exchange interactions are introduced. They are shown able to produce localized magnetic moments, by attracting locally the (traveling) electrons of one spin direction at the expense of the others. A simple condition is obtained for such magnetic moments to appear spontaneously; it is shown to be fulfilled in many transitional metals. With the use of general results obtained recently by the authors and by others, it is then shown that each of these magnetic moments, if produced alone, should extend over a certain region in space, and should be surrounded by “fringes” of spin polarization with an alternating sign. The size of the central region and the wavelength of the fringes are related to an average wavelength of t...

On the knight shift of alloys

Abstract The change and broadening of the Knight shift of silver produced by various solute element. are explained by the fluctuations in electronic density produced at long range by each solute atom. The change in Knight shift observed for Cd, In, Sn and Sb solutes are in satisfactory agreement with those computed using a free electrons approximation for the matrix. From the sign and the values of the changes observed for Pd and Pt solutes, it in concluded that most of the screening arises there from an emptying of their d shells especially for Pt. Finally the change and broadening of the Knight shift of the solute element. are explained in the same way.

On the Description of Covalent Bonds in Diamond Lattice Structures by a Simplified Tight‐Binding Approximation

The simplest possible tight‐binding approximation, using sp hybridized bonds and nearest neighbors overlaps, is used to describe the band structure of diamond, silicon, and germanium. This crude approximation has the great advantage of giving explicit and simple formulas for the Bloch functions and E(k) curves in the whole reciprocal space, as a function of two parameters: an overlap integral λ and an sp promotion energy e. The general band structure is discussed as a function of e/λ. The influence of sp hybridization on the band structure, covalent character of the valence electrons, optical and x‐ray spectra are discussed. It is shown how the energy gap should be related to cohesive energy and pressure. The reasonable agreement with experiment of these various predictions shows the usefulness of the method to understand in a rough and somewhat qualitative way general properties of covalent bonds in crystals.

Charge density wave Madelung constant in a system of linear chains

Abstract The dependence of the Madelung constant upon the relative phase and distance between the charge density waves, occurring on the parallel chains of the chain system, is calculated. The position of the most unstable mode for the Peierls instability is discussed and an expression for the perpendicular correlation length in KCP suggested.

Electron-Phonon Model for High-Tc Layered-Metal Oxides

A simple electron-phonon coupling model is constructed for the layered-metal oxides. The predictions of the model are the tetragonal-to-orthorhombic instability and separately from it, the bond dimerization within the layers. High Tc in those materials is associated with the soft shear phonon branch in their tetragonal state.

Organic superconductors: The (TMTSF)2X family

Abstract This review article is intended to give an elementary introduction to the basic theoretical understanding of the Quasi-One-Dimensional electron gas in organic conductors. It provides a simple theoretical picture of the electron gas instabilities arising at low temperature. Furthermore it gives a survey of the salient experimental results related on the one hand to the Peierls (insulating) instability of TTF-TCNQ and on the other hand to the superconducting instability recently discovered in the family of (TMTSF)2X conducting salts. Special emphasis is put on the consequence of One-Dimensionality for the existence of precursor regimes of the low temperature phase transitions up to temperatures much higher than the phase transition temperatures.

Surface phonon entropy of crystalline lattices at high temperatures

Abstract The phonon contribution to the surface entropy for (100), (110) and (111) planes of bcc, fcc and cubic diamond crystals is calculated at high temperatures and compared with experimental data.