Electron momentum-space densities of Li metal: A high-resolution Compton-scattering study

Abstract

Directional Compton profiles ͑CP's͒ of Li metal were measured for 11 directions of the momentum transfer q with 0.14 a.u. ͑a.u.ϭatomic units: បϭeϭmϭ1͒ momentum-space resolution using synchrotron radiation from the DORIS ͑Doppel-Ring-Speicheranlage͒ storage ring monochromatized to 31 keV. Both the total valence-electron CP's and the directional differences of the CP's exhibit considerable deviations from the most recent density-functional calculations, performed by Sakurai et al. ͓Phys. Rev. Lett. 74, 2252 ͑1995͔͒ within the limits of the local density approximation. These discrepancies are attributed to self-energy effects connected with the excitation of so-called plasmaron modes. The three-dimensional ͑3D͒ valence-electron momentum density, ͑p͒, as well as the 3D occupation number density N͑k͒, were reconstructed using the Fourier-Bessel method. The reconstructed ͑p͒ exhibits clear evidence of higher momentum components due to 110 umklapp processes. The reconstructed N͑k͒ enables a direct experimental access to the Fermi-surface anisotropy of Li, which was found to be 3.6Ϯ1.1%. The reconstructed N͑k͒ for kʈ ͓001͔ was fitted to a model with the renormalization factor z as the only free parameter, which was found to be zϭ0.1Ϯ0.1.

High-Energy Inelastic-Scattering Beamline for Electron Momentum Density Study

“…Similar discrepancy has been observed between recent experimental Compton pro®les Schuelke et al, 1996) and LDA-based band theoretical computations for Li. Both experimental valence Compton pro®les show excellent agreement.…”

“…This feature is in accord with the earlierray Compton work (Hansen et al, 1979) and high-resolution experiments (Loupias & Petiau, 1980) on Be. This is common in studies of other materials (Shiotani et al, 1993;Sakurai et al, 1995;Bellin et al, 1995;Schuelke et al, 1996). Contrary to these results, ultra-high-resolution experiments on Be with a momentum resolution of 0.02 a.u.…”

Quantum Monte Carlo calculation of Compton profiles of solid lithium

“…These discrepancies were attributed to inadequate treatment of correlation in the Kohn-Sham single particle picture [7] and it was proposed that plasmaron (a bound hole-plasmon state) losses could explain the observed difference [8]. Two recent theoretical studies have tried to explain this discrepancy but reached opposite conclusions.…”

“…Being a low-Z material, lithium has been the subject of Compton studies since the early days of x-ray Compton scattering [6]. Recent high-resolution experiments have been conducted on lithium and Fermi surface signatures have been investigated either by analyzing first and second derivatives of the Compton profiles [7] or attempting a reconstruction of the momentum distribution [8].…”

Full-potential LAPW calculation of electron momentum density and related properties of Li

“…The advent of high intensity, high energy and well-polarized synchrotron sources and the spectrometers with high resolution (∼ 0.12a.u.) have resulted in revival of interest in this area [13][14][15] . On the theoretical side, high performance computing facilities have made it possible to perform calculations on a fine p-mesh with a better convergence criteria for the total energy and charge density self-consistency.…”