Quasiparticle State in 4f Localized Ferromagnet CeRu2Ge2 Studied by Soft X-ray Photoemission Spectroscopy

The electronic state of 4f localized ferromagnet CeRu2Ge2 has been investigated by angle-resolved photoemission spectroscopy (ARPES) experiments using soft x rays. The band structure and Fermi surfaces consisting of non-4f bands are almost consistent with a calculation based on the density-functional theory for LaRu2Ge2, thus confirming a localized character of the 4f electrons. On the other hand, the Ce 3d–4f resonant ARPES experiments demonstrated that the 4f spectral function is dominated by f1 components in the vicinity of the Fermi level and thus is different from that expected for a localized electron system. We also revealed that the intensities of the f1 components have almost no temperature dependence up to at least 100 K, which is two orders of magnitude larger than the Kondo temperature of CeRu2Ge2.