THE OPTICAL-PROPERTIES OF RUSI - KONDO INSULATOR OR CONVENTIONAL SEMICONDUCTOR

We have investigated the electrodynamic response of single-phase RuSi in its low and high temperature phases. While the high-temperature pha se (CsCl-type) is a simple metal, the low-temperature phase (FeSi-type ) is a semiconductor which shows at room temperature a narrow gap of a pproximately 0.4 eV, while an even smaller gap of approximately 20 meV appears in the optical spectra below 100 K. Extrinsic-like inclusions , due to deviations from the ideal stoichiometry in the RuSi-matrix, l ead to a remaining low frequency spectral weight of metallic nature in the FeSi-type RuSi. (C) 1998 Published by Elsevier Science Ltd.