Full gap opening in single crystalline Fe1-xCoxSi evidenced by high-resolution photoemission

We have investigated high-quality tri-arc-Czochralski grown single crystals of Fe1-xCoxSi by high-resolution photoemission spectroscopy using synchrotron radiation. The Fermi edges of FeSi and Fe0.95Co0.05Si were measured with an energy resolution of 10meV. The spectra evidence for the first time a full band gap in FeSi. A closing of this gap by doping with 5at% Co could clearly be established. Band structure calculations with different techniques describe the measured spectra differently well. Agreement with the experiment is achieved by generalized gradient approximation (GGA) method.