MICROWAVE COMPLEX CONDUCTIVITY OF GAPPED STATE IN CENISN

The temperature dependence of the microwave complex conductivity sigma (T) = sigma(1)(T) - i sigma(2)(T) was determined at 9.6 and 14 GHz in a single crystal of CeNiSn from the surface impedance measurements. Be low about 10 K the real part sigma(1) is suppressed in comparison with the de conductivity and the imaginary part sigma(2) increases rapidly . These results indicate a rapid decrease of scattering of quasipartic les, whose excitation spectrum is drastically changed from the heavy-f ermion to a gapped state at low temperatures.