We propose a microscopic description of heavy fermions in UPt_3. It is based on the assumption that two of the three 5f electrons of the U ions are localized. Band-structure calculations based on this supposition reproduce the observed de Haas-van Alphen frequencies very well. The observed enhancement of the quasiparticle mass as compared with the LDA band mass results from the local Coulomb interaction of the delocalized f electrons with the localized ones. Diagonalization of the Coulomb interaction matrix yields the level scheme of the localized f^2 states. Assuming a splitting of the ground-state doublet by the crystal field of similar size as in UPd_2Al_3 results in a mass enhancement factor of order 10 in agreement with experiments.
@article{arxiv.cond-mat/0107378,
title = {Origin of heavy quasiparticles in UPt_3},
author = {G. Zwicknagl and A. N. Yaresko and P. Fulde},
journal= {arXiv preprint arXiv:cond-mat/0107378},
year = {2007}
}