Electronic structures of ferromagnetic superconductors UGe_2 and UCoGe studied by angle-resolved photoelectron spectroscopy

摘要

The electronic structures of the ferromagnetic superconductors UGe_2 and UCoGe in the paramagnetic phase were studied by angle-resolved photoelectron spectroscopy using soft x rays (hv = 400-500 eV). The quasiparticle bands with large contributions from U 5 f states were observed in the vicinity of E_F, suggesting that the U 5 f electrons of these compounds have an itinerant character. Their overall band structures were explained by the band-structure calculations treating all the U 5 f electrons as being itinerant. Meanwhile, the states in the vicinity of E_F show considerable deviations from the results of band-structure calculations, suggesting that the shapes of Fermi surface of these compounds are qualitatively different from the calculations, possibly caused by electron correlation effect in the complicated band structures of the low-symmetry crystals. Strong hybridization between U 5 f and Co 3d states in UCoGe were found by the Co 2p - 3d resonant photoemission experiment, suggesting that Co 3d states have finite contributions to the magnetic, transport, and superconducting properties.