Unoccupied Band Structure of NbSe2 by Very-Low-Energy Electron Diffraction: Experiment and Theory

TL;DR

This study combines experimental electron diffraction and ab initio calculations to analyze the unoccupied band structure of NbSe2, revealing energy-dependent quasiparticle lifetimes and plasmon-related features.

Contribution

It provides new insights into the unoccupied electronic states and quasiparticle lifetimes of NbSe2 through combined experimental and theoretical approaches.

Findings

Identification of a sharp increase in optical potential at 20 eV

Correlation of spectral broadening with quasiparticle lifetimes

Ab initio calculation of electron energy loss spectrum and reflectivity

Abstract

A combined experimental and theoretical study of very-low-energy electron diffraction at the (0001) surface of 2H-NbSe2 is presented. Electron transmission spectra have been measured for energies up to 50 eV above the Fermi level with k|| varying along the GammaK line of the Brillouin zone. Ab initio calculations of the spectra have been performed with the extended linear augmented plane wave k-p method. The experimental spectra are interpreted in terms of three-dimensional one-electron band structure. Special attention is paid to the quasi-particle lifetimes: by comparing the broadening of the spectral structures in the experimental and calculated spectra the energy dependence of the optical potential Vi is determined. A sharp increase of Vi at 20 eV is detected, which is associated with a plasmon peak in the Im(-1/epsilon) function. Furthermore, the electron energy loss spectrum and the reflectivity of NbSe2 are calculated ab initio and compared with optical experiments. The obtained information on the dispersions and lifetimes of the unoccupied states is important for photoemission studies of the 3D band structure of the valence band.