Localized 5 states in UPdAl and valence crossover in the Vicinity of Heavy-Fermion superconductivity

Metoki, Naoto   ; Haga, Yoshinori   ; Yamamoto, Etsuji  ; Matsuda, Masaaki*

The localized 5 states with 5 () configuration of U ion have been revealed in UPdAl. We found that the low-lying states are the same as PrPdAl flat orbitals with large are stabilized by a two-dimensional CEF potential in the unique crystal structure. The present study involves the valence crossover from tetravalent to trivalent in a series of AnPdAl, demonstrated by lattice and/or transport anomaly as well as many body effects in the vicinity of the boundary. The valence instability plays important role for the unusual heavy fermion superconductivity in NpPdAl.