Photoemission Study of the Itinerant Helimagnetic MnSi

We have studied the electronic structure of MnSi, which shows a helical spin ordering below 30 K, by ultraviolet photoemission spectroscopy. We have attempted to separate the spectra into surface and bulk components by considering the electron mean-free path and the thickness of the outermost atomic layer. The `bulk' spectra thus obtained are compared with the density of states given by band-structure calculation corrected for model self-energies and reasonable agreement was obtained. This indicates that both band structure and electron correlation effects are important to understand the physical properties of MnSi. The spectra in the entire valence-band region do not show appreciable temperature dependence, but the spectral weight in the vicinity of the Fermi level is slightly decreased with decreasing temperature, which we tentatively attribute to the exchange splitting of the Mn 3 d bands.