Towards strongly correlated semimetals: U₂Ru₂Sn and Eu₈Ga₁₆Ge₃₀

We present results of transport, magnetic, and calorimetric measurements on two f-electron based compounds: U₂Ru₂Sn and Eu₈Ga₁₆Ge₃₀. We show that U₂Ru₂Sn shares several properties with the strongly correlated semimetal CeNiSn. These analogies suggest that in U₂Ru₂Sn a narrow energy gap (or pseudogap) opens which is one order of magnitude larger than the one of CeNiSn. The two modifications of the clathrate Eu₈Ga₁₆Ge₃₀ behave as local-moment ferromagnetic metals with relatively low Curie temperatures and small charge-carrier concentrations. The thermal conductivity is low and glass-like, as expected for 'filled-cage' systems. If, by modification of the Ga-Ge cages, a 'Kondo insulating' ground state could be realized, a high thermoelectric figure of merit associated with the (pseudo)gap opening would be expected.