Paper AC+AS+SA-WeA10
Exotic Electronic Properties of Strongly Correlated Compounds NpPd₃ and PuPd₃

Wednesday, October 24, 2018, 5:20 pm, Room 202C

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 complex phenomena that are observed in these strongly correlated materials, spanning magnetic ordering, heavy-fermion ground state, unconventional superconductivity, and/or "non-Fermi liquid" state. The electronic properties of the strongly correlated electron systems are related to the formation, near the Fermi level, of a narrow band with large density of states and in spite of intensive theoretical and experimental efforts their nature is still not well understood. This behavior is well emphasized in AnPd₃ (An-U, Np, Pu) system. UPd₃ crystalizes in the hexagonal crystal structure and shows four phase transitions below 7.8 K, attributed to a succession of antiferroquadrupolar orderings of the uranium ions localized on the quasi-cubic sites of the dhcp structure. Depending on a heat treatment, NpPd₃ crystalizes in hexagonal and cubic crystal structures. The hexagonal NpPd₃ (h-NpPd₃) exhibits two transitions at 30 and 10 K. It has been suggested that the low temperature transition might be due to ordinary antiferromagnetic ordering while the high temperature one might be caused by a quadrupolar order. The cubic NpPd₃ (c-NpPd₃) orders antiferromagnetically below 52 K and the magnetic and transport measurements suggests that the transition is first order. PuPd₃ crystalizes in the cubic structure and shows an antiferromagnetic order below 24 K. To explore the influence of electronic correlations on the physical properties in the AnPd₃ system, here we present our detailed magnetic, thermodynamic, and transport studies of NpPd₃ and PuPd₃.We show that all results obtained present characteristic behaviors of 4f- and 5f-electron strongly correlated materials. The magnitude and overall temperature dependence of the electrical resistivity, magnetostesitivity, Hall and Seebeck effect, and heat capacity of NpPd₃ and PuPd₃ are archetypal of materials with Kondo interactions. Our measurements also reveal an unusual magnetic ordering in c-NpPd₃. At T_N, the specific heat exhibits an extremely large peak [as large as 1000 J/(mol K)] and the magnetic susceptibility shows a clear jump. The transport properties of c-NpPd₃ indicate a dramatic reconstruction of the electronic structure at the Néel temperature, probably accompanied by a large change in the Fermi surface topology, which shows up as pronounced anomalies at this temperature in the electrical resistivity, the magnetoresistivity, and the Seebeck and the Hall coefficient. We will discuss implications of these results.