${\mathrm{Fe}}_{1-x}{\mathrm{Co}}_x\mathrm{Si}$ single crystals with different Co concentrations were grown using the tri-arc Czochralski technique. Samples with 0, 5, and $20\mathrm{at.}\%$ of Co were studied with photon energies of 21.2 and $40.8\mathrm{eV}$ with spectral resolutions as high as $8\mathrm{meV}$ at the Fermi level. For FeSi, a full gap of $28\mathrm{meV}$ has been found, which closes with 5% of Co. In the range between 20 and $150\mathrm{eV}$, 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 $\mathrm{Fe}3d$ states. No sign of Kondo resonance is found.

• Received 21 February 2007

DOI:https://doi.org/10.1103/PhysRevB.75.165103