Electronic structure of correlated electron materials from photoemission in high-quality single crystals

Much of our understanding of heavy fermion systems over the past two decade s has been based on the single impurity model and its approximate solutions . We show with numerous examples of photoelectron spectra, especially with YbInCu4, that this model is not applicable to stoichiometric heavy fermion compounds. There is overwhelming evidence that the correct description of h eavy fermions must include very narrow, hybridized bands which exist alread y at temperatures far above the thermodynamically determined Kondo temperat ure, and that these bands are relatively temperature independent. Some form of the periodic Anderson model (PAM) is needed, one which results in very narrow renormalized LDA bands. We compare our data to one form of the PAM. (C) 2001 Elsevier Science B.V. All rights reserved.