Xenon-plasma-light low-energy ultrahigh-resolution photoemission study ofCo(S1−xSex)2(x=0.075)

Abstract

We have performed low-energy ultrahigh-resolution photoemission spectroscopy on $\mathrm{Co}{({\mathrm{S}}_{1\ensuremath{-}x}{\mathrm{Se}}_{x})}_{2}$ $(x=0.075)$ to elucidate the bulk electronic states responsible for the ferromagnetic transition. By using a newly developed plasma-driven low-energy xenon (Xe) discharge lamp $(h\ensuremath{\nu}=8.436\phantom{\rule{0.3em}{0ex}}\mathrm{eV})$, 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 $\mathrm{He}I\ensuremath{\alpha}$ resonance line $(h\ensuremath{\nu}=21.218\phantom{\rule{0.3em}{0ex}}\mathrm{eV})$ indicates that the sharp quasiparticle is of bulk origin and is produced by the Fermi-level crossing of the Co $3d$ ${e}_{g\ensuremath{\downarrow}}$ subband.