Electron transport and magnetic properties of the filled skutterudite compound ThFe4As12

Single crystals of the filled skutterudite compound ThFe4As12 were examined down to T = 0.4 K and in magnetic fields up to B = 9 T. Electron transport properties combined with results of Hall-effect measurements indicate semimetallic properties with a charge carrier density of the order of 2 × 1020 cm−3. In terms of a two-band model, the effective mass of the electrons is nearly a factor of 5 larger than the hole effective mass. A small carrier density is in line with the lack of magnetic ordering in this Fe-based filled skutterudite. Therefore, a Sommerfeld coefficient of the electronic specific heat of 45 mJ/mJ K2 for semimetallic ThFe4As12 is an unexpected observation whose origin remains to be explained.