Electronic states of EuCu2Ge2 and EuCu2Si2 studied by soft x-ray photoemission spectroscopy

摘要

We have carried out angle-integrated photoemission spectroscopy (AIPES) and angle-resolved photoemission spectroscopy (ARPES) experiments using soft x rays on single crystals of EuCu2Ge2 and EuCu2Si2 grown by the Bridgman method to investigate their electronic structures. The AIPES results showed that the Eu ions in EuCu2Ge2 and EuCu2Si2 are in a divalent state and a nearly trivalent state, respectively, in accordance with the previously reported magnetic properties. The three-dimensional band structures and shapes of the Fermi surfaces of EuCu2Ge2 and EuCu2Si2 were studied by ARPES measurements. We found that the band structures near the Fermi level and Fermi surfaces of EuCu2Ge2 and EuCu2Si2 are very different from each other and are well reproduced by the band structure calculations based on density-functional theory for SrCu2Ge2 and YCu2Si2. This suggests that a charge transfer from the localized 4f states into the valence bands is responsible for the difference in the electronic states between EuCu2Ge2 and EuCu2Si2.