Absence of Kondo resonance in high-resolution photoemission spectra of monocrystalline Fe1-xCoxSi

Fe1-xCoxSi single crystals with different Co concentrations were grown using the tri-arc Czochralski technique. Samples with 0, 5, and 20 at. % of Co were studied with photon energies of 21.2 and 40.8 eV with spectral resolutions as high as 8 meV at the Fermi level. For FeSi, a full gap of 28 meV has been found, which closes with 5% of Co. In the range between 20 and 150 eV, energy dependent angle-resolved measurements in the [111] direction were made for FeSi. Through a comparison with theoretical calculations, the states at the Fermi energy can be directly assigned to Fe 3d states. No sign of Kondo resonance is found.