LOCALIZATION EFFECTS IN KONDO SEMIMETALS CENISN AND CERHSB

We have found that the semiconductor-like increase in resistivity prev iously reported on CeNiSn and CeRhSb below about 8 K is suppressed wit h decreasing impurity concentration in single-crystalline samples. Nev ertheless, the absolute values of the Hall coefficient strongly increa se as temperature decreases. Therefore, we interpret the metallic beha vior found in the a-axis resistivity of a purified crystal of CeNiSn a s a consequence of the significant increase of relaxation time of carr iers. Even for the purified crystal, the residual gamma value is 40 mJ /K-2 mol at 0.03 K. These results suggest that the energy gap is close d along the a-axis and that residual carriers are strongly localized i n the presence of impurities.