Electronic structure of EuAl₄ studied by photoelectron spectroscopy

The electronic structure of the divalent Eu compound EuAl₄, which shows a charge density wave transition at T_CDW = 140 K, was studied by hard X-ray angle-integrated photoelectron spectroscopy (HAXPES) and soft X-ray angle-resolved photoelectron spectroscopy (ARPES). The valence band and core-level spectra obtained by HAXPES are consistent with the divalent nature of Eu atoms in EuAl₄. From the ARPES results, the Fermi surface as well as band structure in the vicinity of the Fermi energy (E_F) of EuAl₄ are very similar to those of its isostructural divalent Sr compound SrAl₄, which has no 4f electrons. This suggests that the Eu atoms are divalent in EuAl₄, and the 4f electrons are localized below 1.8 eV with the Eu 4f⁷ electronic configuration in the ground state. The ARPES spectra measured along the Γ-(Σ)-Z high-symmetry line did not show significant temperature dependences above and below T_CDW within the energy resolution of 80-90 meV. Moreover, the Fermi surface mapping along the k_z direction showed that both EuAl₄ and SrAl₄ have mostly three-dimensional electronic structures, suggesting that the nesting of the Fermi surface is not simple. The Fermi surface and the band structure of EuAl₄ were well explained by the band-structure calculation of SrAl₄ based on the local density approximation.