Specific heat of SmB₆ at very low temperatures

Ground state properties of the intermediate valence narrow-gap semiconductor SmB₆ have been experimentally studied by means of specific heat C ( T ) measurements down to 0.04 K and in magnetic field up to 6 T. The most remarkable feature of the observed results are the high values of C ( T ) below 2 K with a small increase below about 0.1 K for both investigated samples. This behaviour can be attributed to the formation of a coherent state within the metallic-like in-gap states of SmB₆ and suggests growth of the electronic part of specific heat γ like in heavy fermion systems. The in-gap states seem to be influenced by impurities which, together with nuclei of boron and samarium isotopes, contribute to the magnetic part of C ( T ). Moreover, impurities play an important role in the hyperfine interaction in SmB₆.