HIGH-MAGNETIC-FIELD STUDIES OF THE KONDO SEMICONDUCTOR CENISN

The Kondo-lattice compound CeNiSn behaves as a narrow-gap semiconducto r at low temperatures below 7 K. The effect of magnetic field on the g apped state of this compound has been studied by the measurements of m agnetization, magnetoresistance and specific heat on a single-crystall ine sample. A weak metamagnetic transition and very large negative mag netoresiostance are observed only when a magnetic field higher than 13 T is applied along the a axis of the orthorhombic structure. These re sults show that the pseudogap is suppressed anisotropically by the mag netic field. The collapse of the gap is accompanied with the evolution of a polarized heavy-fermion state.