V. Pavlík

Ground state formation in intermediate valent SmB6

Abstract Electrical resistivity measurements have been carried out on the intermediate valent small gap compound SmB 6 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 SmB 6 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.

Investigation of in-gap states in SmB6 ∗ )

We have investigated the low temperature properties of the narrow-gap semiconductor SmB6 by means of electrical resistivity and specific heat measurements. Results imply that the residual resistivity below about 3 K is non-activated and the corresponding state, which is formed within the in-gap states, has a metallic-like nature. Heat capacity measurements confirmed the metallic-like properties of the in-gap states and revealed, moreover, an enhancement of the specific heat below 2 K which is more expressive for the sample with a lower amount of impurities. The observed behaviour can be attributed to the formation of a coherent state within the in-gap states of this compound.

Low-temperature magnetic properties of SmB6

Abstract We have performed measurements of the magnetic susceptibility of three SmB 6 single crystals with various purities in the temperature range between 300 and 2 K. In the high-temperature region the observed data follow the Curie–Weiss-like dependence indicating a local-moment behavior. Below 10 K, where a temperature-independent behavior due to Van Vlecks theory is expected, all samples exhibit an increase of magnetization which can be accounted for by a small amount of bare Sm 3+ ions, magnetic 4f 5 5d 1 states or by magnetic rare-earth impurities.

The energy gap of SmB6 at low temperatures

Abstract We have studied the energy gap of the intermediate valent small-gap semiconductor SmB6 by means of electrical resistivity measurements. The data received from the investigation of three single-crystalline samples have shown that at lowest temperatures the resistivity exhibits an activated behaviour with an energy gap of a few mK. The structure and origin of the in-gap states are discussed.