Two-dimensional angular distribution of photoelectrons of single-crystal graphite

Abstract

Two-dimensional band structures of single-crystalline graphite have been directly observed by using a new version of a two-dimensional display-type spherical mirror analyser. The intensity distribution patterns at various binding energies below the Fermi level for the excitation by linearly polarized synchrotron radiation normally incident on the cleaved surface have shown crystal-symmetry-broken angular distributions. The non-sixfold symmetry can be understood as being the result of the angular dependence of the probability of the electric dipole transition from each atomic orbital with a particular symmetry or s) for the s-polarized synchrotron radiation. In order to understand the uneven intensity in different Brillouin zones, we consider a model including the tight-binding initial state and a free-electron-like final state. It is found that such unusual distribution patterns are explained by the new concept of a `photoemission structure factor' with consideration of the phase of the coefficients of the atomic orbitals of inequivalent atoms in a unit cell in the initial-state Bloch function.