Angle-resolved photoemission in the multi-keV regime: first experimental data and theory for W and GaAs

ARPES is the technique of choice for studying the electronic structure of solids and surfaces. However, the measurements are very surface sensitive, probing only about 1 nm into the material. In order to study bulk properties, the use of highenergy photons in the multi-keV regime is suggested. ARPES in the multi-keV regime is now possible via hard X-ray undulator beamlines, together with angle-resolving spectrometers. We will present first hard X-ray ARPES experiments on a tungsten(110) and a GaAs(001) crystal at energies of up to 6 keV. Data obtained at 30 K clearly show band structure effects for both materials, as well as photoelectron diffraction effects for corelevels and more localized valence-band states. The data are compared with the results of both free-electron final-state theory and one-step theory including matrix element effects. Methods for correcting low-temperature data for residual phonon effects are considered.