No abstract

No abstract

Rapid Communications are intended for the accelerated publication of important new results and are therefore given priority treatment both in the editorial office and in production AR. apid Communication in Physical Review B should be no longer than four printed pages and must be accompanied by an abstract Pag. e proofs are sent to authorsWe report the observation of strong amplitude variations with k in the 4f photoelectron spectra of a nearly trivalent heavy-fermion compound (CePt2+"). The amplitude of the 4f feature, previously identified as the Kondo resonance, displays the full symmetry of the lattice, suggesting some band character already at T= 10' . Kondo lattice-derived bands are expected to exist only at T(& Tz, so that this would seem to favor conventional bands at high T. The single-impurity model by contrast demands purely localized behavior at these temperatures.

We present high-resolution, angle-resolved photoemission spectra for Ce-based and U-based strongly correlated electron systems. The experimental results are irreconcilable with the long-accepted single-impurity model, which predicts a narrow singlet state, in close proximity to the Fermi energy, whose linewidth and binding energy are a constant determined by a characteristic temperature T K for the material. We report that both 4 f and 5 f photoemission features disperse with crystal momentum at temperatures both above and below T K ; these are characteristics consistent with narrow bands but not with the single-impurity model. Inclusion of the lattice must be considered at all temperatures. Variants of the periodic Anderson model are consistent with this approach. ͓S0163-1829͑97͒51536-0͔