Bulk electronic structure studied by hard X-ray photoelectron spectroscopy of the valence band: The case of intermetallic compounds

Highlights: •Bulk sensitivity of HAXPES was used to explore the electronic structure of several Heusler compounds in form of bulk materials and thin films. •Strong changes of the electronic structure Heusler shape memory Mn2NiGa appear at the phase transition. •HAXPES of C1b Heusler compounds with narrow band gap showed the existence of in gap states close to the Fermi energy. •Linear dichroism in hard X-ray photoelectron spectroscopy (LDAD-HAXPES) was used to study the angular asymmetry in photoemission from the valence states of three kinds of Heusler compounds. -- Abstract: Photoelectron spectroscopy (PES) has evolved into the most relevant, powerful, and nondestructive method for investigating atoms, molecules, and solids. In particular, hard X-ray photoelectron spectroscopy (HAXPES) has emerged as a powerful tool for investigating the bulk electronic structure of materials in a variety of applied fields such as chemistry, physics, and materials science. In addition, PES was used for investigating the symmetries of various materials' electronic structures. However, thus far, such studies have been restricted to atoms, molecules, adsorbates, and surfaces because low-energy (<1 keV) electrons have limited probing depths. This is disadvantageous because three-dimensional (3D) bulk states cannot be studied. The present work demonstrates that this drawback can be eliminated by using hard X-rays with variable polarization for excitation. In the current study, this issue was investigated using several Heusler compounds, which have been attracting increasing levels of interest. There are more than 2000 Heusler compounds in total. Owing to their tunable electronic structures, Heusler compounds exhibit multifarious properties useful for spintronic, optoelectronic, shape memory, and thermoelectric applications. Herein, we report the results of bulk-sensitive, high energy photoelectron spectroscopy of the valence bands of several Heusler compounds for various applications. It is shown that the measured valence band spectra are clearly resolved and are in good agreement with the first-principles calculations of the compounds' electronic structures