LOW-ENERGY EXCITATION IN KONDO SEMICONDUCTORS CENISN AND CERHSB

Low-energy excitation in Kondo semiconductors CeNiSn and CeRhSb, has been investigated by the measurement of Sn-119 and Sb-123 nuclear spin-lattice relaxation rate, 1/T1. From a T3-like temperature dependence of 1/T1 for both compounds, it has been intuitively concluded that the pseudo energy gap with the V-shaped structure is formed in the effective density of states for heavy quasi-particles. The band width of D=210 K and the pseudo energy gap of DELTA=28 K in CeRhSb are almost two times larger than those of CeNiSn (D=140 K and DELTA=14 K), respectively. Below 0.4 K and 0.8 K for CeNiSn and CeRhSb, respectively, the T1T=const. behavior has been commonly observed in the two compounds, indicative of the presence of a residual density of states at the Fermi level. Impurities and/or imperfection in the samples easily mask the intrinsic V-shaped structure of the energy gap at very low temperatures.