Scientific Highlight 07/2011
We succeeded recently to use hard X-rays with variable photon polarization to excite electrons from the bulk of Heusler compounds. The high bulk sensitivity of the new hard X-ray photoelectron spectroscopy (HAXPES) experiment combined with linearly polarized photons will have a major impact on the study of the electronic structure of bulk materials, thin films, deeply buried materials, and interfaces.
The symmetry of electronic states is of fundamental interest in many disciplines of physics. Although photoelectron spectroscopy finds many applications, particularly for the investigation of the symmetries of electronic structures of materials, its use has been limited to atoms, molecules, and surfaces because of the use of low-energy electrons. It cannot thus be used to investigate 3D bulk states. We used HAXPES in combination with the linear dichroism in the angular distribution (LDAD) of photoelectrons to investigate the symmetry of the valence states of the Heusler compounds NiTiSn and NiMnSb. In the present study, LDAD in hard-x-ray photoelectron spectroscopy was used to investigate the angular asymmetry in photoemission from the valence states of polycrystalline Heusler compounds. The polarization-dependent measurements reveal that even high energies and polycrystalline samples do not yield a one-to-one correspondence of photoemission spectra and density of states. It was shown that the change in the linear polarization allows for different states of the valence band of complex materials to be easily distinguished. Published as S. Ouardi et al.; "Study of symmetry of valence states of Heusler compounds based on linear dichroism in hard X-ray photoelectron spectroscopy" in Phys. Rev. Lett. 107 (2011) 036402.
