Tunneling spectroscopy on the correlation effects in FeSi

We report for the first time on temperature-dependent spectroscopy of charg e excitations in FeSi single crystals probed with a low-temperature STM bet ween 4 and 300 K. Below approximate to 200 K, two peaks start to emerge in the differential conductance (dI/dV) on either side of the Fermi level, whi ch grow with decreasing temperature and are separated by a (pseudo-)gap of approximate to 50 meV. We ascribe this change in the tunneling spectra to t he formation of quasiparticle density of states caused by d-electron correl ations. We find good agreement with photoemission spectroscopy since both m ethods are sensitive to the correlated d-electron density of states (DOS). Our results are also consistent with optical reflectivity data and Raman sp ectroscopy which, in contrast, are sensitive to the conduction (c) electron DOS. (C) 1999 Elsevier Science B.V. All rights reserved.