Transport properties of strongly correlated compounds AnPd₃ (An = Pu, Np)

Actinides are characterized by the coexistence of localized and itinerant (delocalized) 5f-states near the Fermi energy. This dual nature of the 5f electrons leads to many exotic phenomena that are observed in these strongly correlated materials, spanning magnetic ordering, heavy-fermion ground state, unconventional superconductivity, and/or a "non-Fermi liquid" state. The unusual transport properties of the strongly correlated electron systems are related to the formation, near the Fermi level, of a narrow band with a large density of states. Therefore, the Seebeck coefficient in these materials, being proportional to the density of states at the Fermi level, often reaches large values and shows the characteristic temperature dependence [Phys. Rev. B 94, 195117 (2016)]. To explore the influence of electronic correlations on the transport properties in the AnPd₃ system, here we present low-temperature electrical resistivity and Seebeck coefficient measurements of NpPd₃ and PuPd₃ intermetallics. We show that the electrical resistivity shows characteristic behavior of systems with Kondo interactions. The magnitude and overall temperature dependence of the thermoelectric power of NpPd₃ and PuPd₃ are characteristic of 4f- and 5f-electron strongly correlated materials. For cubic NpPd₃ a sharp transition and change of sign in S(T) at the Néel temperature indicate a first-order nature of the magnetic transition, probably accompanied by a large change in the Fermi surface topology. We have also estimated the power factor (S²/ρ) of these materials.