A Novel 2D Folding Technique for Enhancing Fermi Surface Signatures in the Momentum Density: Application to Compton Scattering Data from an Al-3at%Li Disordered Alloy

We present a novel technique for enhancing Fermi surface (FS) signatures in the 2D distribution obtained after the 3D momentum density in a crystal is projected along a specific direction in momentum space. These results are useful for investigating fermiology via high resolution Compton scattering and positron annihilation spectroscopies. We focus on the particular case of the (110) projection in an fcc crystal where the standard approach based on the use of the Lock-Crisp-West (LCW) folding theorem fails to give a clear FS image due to the strong overlap with FS images obtained through projection from higher Brillouin zones. We show how these superposed FS images can be disentangled by using a selected set of reciprocal lattice vectors in the folding process. The applicability of our partial folding scheme is illustrated by considering Compton spectra from an Al-3at%Li disordered alloy single crystal. For this purpose, high resolution Compton profiles along nine directions in the (110) plane were measured. Corresponding highly accurate theoretical profiles in Al-3at%Li were computed within the local density approximation (LDA)-based Korringa-Kohn-Rostoker coherent potential approximation (KKR-CPA) first-principles framework. A good level of overall accord between theory and experiment is obtained, some expected discrepancies reflecting electron correlation effects notwithstanding, and the partial folding scheme is shown to yield a clear FS image in the (110) plane in Al-3%Li.Comment: 24 pages, 8 figures, to appear in Phys. Rev.

IS THE EXISTENCE OF A UNIFORM MAGNETIZATION IN 3d-METALS EVIDENT FROM THE EXPERIMENTAL FORM FACTOR ?

Les méthodes différentes pour l'analyse des facteurs de forme des métaux-3d sont décrit. Les résultats de la méthode classique pour le Ni et le Fe, données dans la littérature indiquent dans ces métaux l'existence d'une densité magnétique uniforme α. Une méthode, développée récemment (Méthode d'Opérateur de Projection), donne comme conclusion que cette densité est nulle. Les deux méthodes ont été analysé et la cause de cette différence est présenté. La sensibilité à α de la dernière méthode a été déterminé comme suffisant.The different methods for the analysis of magnetic form factors of 3d-metals are described. The results of the form factor fitting method as given in the literature indicate the presence of a uniform negative spin density α in Ni and Fe. The recently developed Projection Operator Method leads to the conclusion that such a uniform density is not present. In this paper both methods are analyzed and the cause of this discrepancy is given. The sensitivity for α of the POM is tested and found to be good

Saving costs in cancer patient management through molecular imaging

Item does not contain fulltex

Electron momentum density in Cu0.9Al0.1

A reconstruction technique based on the solution of the Radon transform in terms of Jacobi polynomials is used to obtain the 3D electron momentum density rho(p) from nine high-resolution Compton profiles (CPs) for a Cu0.9Al0.1 disordered alloy single crystal. The method was also applied to theoretical CPs computed within the Korringa-Kohn-Rostoker coherent potential approximation (KKR-CPA) first-principles scheme for the same nine orientations of the crystal. The experimental density rho(p) is in satisfactory agreement with the theoretical density and shows most details of the Fermi surface (FS) and exhibits electron correlation effects. We comment on the map of the FS obtained by folding the reconstructed rho(p) into the first Brillouin zone which yields the occupation number density, rho(k). A test of the validity of data via a consistency condition (within our reconstruction algorithm) as well as the propagation of experimental noise in the reconstruction of both rho(p) and rho(k) are investigated

Fermi-surface and electron correlation in A1 studied by Compton scattering

We have studied the electron-momentum density distribution in Al using the coincidence as well as the conventional high-resolution Compton scattering technique. In order to interpret the results, corresponding band theory based computations of the electron momentum density (EMD) and the Compton profiles (CPs) have been carried out. Our focus here is on determining the size of the break ZF in the EMD at the Fermi momentum. For this purpose, differences between measurements and theoretical predictions are analyzed in terms of a simple model for describing electron correlation effects which are missing from the independent particle band theory framework; the model involves ZF as the only adjustable parameter. A good fit with the coincidence measurements is obtained for ZF of about 0.7, while the CP data yields ZF = 0.7 to 0.8. This study suggests that, in sharp contrast to the case of Li where recent high-resolution Compton work indicates ZF≈0, the standard picture of the interacting electron gas is substantially correct in Al