Origin of heavy quasiparticles in UPt₃

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We propose a microscopic description of heavy fermions in UPt₃. 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 f² states. Assuming a splitting of the ground-state doublet by the crystal field of similar size as in UPd₂Al₃ results in a mass enhancement factor of order 10 in agreement with experiments.