Xenon-plasma-light low-energy ultrahigh-resolution photoemission study of Co (S1-x Sex) 2 (x=0.075)

We have performed low-energy ultrahigh-resolution photoemission spectroscopy on Co (S1-x Sex) 2 (x=0.075) to elucidate the bulk electronic states responsible for the ferromagnetic transition. By using a newly developed plasma-driven low-energy xenon (Xe) discharge lamp (hν=8.436 eV), we clearly observed a sharp quasiparticle peak at the Fermi level together with the remarkable temperature dependence of the electron density of states across the transition temperature. Comparison with the experimental result by the HeIα resonance line (hν=21.218 eV) indicates that the sharp quasiparticle is of bulk origin and is produced by the Fermi-level crossing of the Co 3d eg subband.