Valence-band electronic structure ofNiSi2andCoSi2: Evidence of the Siselectronic state at the Fermi edge

It is found that the Si ${\mathit{L}}_{2,3}$ soft-x-ray emission band of a ${\mathrm{NiSi}}_2$ single crystal has two main peaks at hν≃91 and 100 eV, where the Si ${\mathit{L}}_{2,3}$ spectrum is expected to reflect the density of states of the valence band with s and d symmetry. The sharp peaks at the top of the valence band are concluded to be due to the s band that mainly originated from the Si s state and are not due to the d band that originated from the Ni d state, which is a clear departure from the existing widely accepted explanation of the valence-band density of states. A similar result may be true for ${\mathrm{CoSi}}_2$.