OBSERVATION OF A GAP OPENING IN FESI WITH PHOTOELECTRON-SPECTROSCOPY

We report the results of high-resolution photoemission measurements on the narrow-gap semiconductor FeSi. Contrary to previous photoemission studies performed on polycrystalline samples, we observe an incomplet e opening of the energy gap in monocrystalline samples at low temperat ure. This gap is of similar size to that measured in optical experimen ts and, in further agreement with optical experiments, is closed at 30 0 K. A direct comparison of the spectra from single and porycrystallin e samples suggests that a well-ordered surface is crucial for the obse rvation of this pseudogap by photoemission.