Ground state formation in intermediate valent SmB6

Electrical resistivity measurements have been carried out on the intermediate valent small gap compound SmB6 at temperatures between 90 and 0.08 K. From the local activation energy we were able to determine directly the width of the hybridization gap which controls the conductivity between 70 and 15 K, and the distance between the bottom of the conduction band and in-gap states which are formed in this energy gap and provide extrinsic conduction in the temperature range 15-3 K. Below about 3 K the activation energy of all the samples decreases rapidly to values which are much lower than the available thermal energy. This result implies that the residual conductivity of SmB6 is of non-activated (metallic) nature. The metallic behaviour can be attributed to a many-particle ground state formed from the in-gap states of this compound. (C) 2001 Elsevier Science B.V. All rights reserved.