Strongly renormalized quasiparticles in UPt3

We performed angle-resolved photoemission spectroscopy (ARPES) experiments using soft x rays to investigate the electronic structure of the heavy-fermion superconductor UPt3. The overall band structure revealed by the present ARPES measurements is compared with density-functional calculations for UPt3 and the non -5 f reference compound ThPt3. We showed that the calculation for ThPt3 gives a better description of the experimental band structure, except for the 5 f-derived heavy quasiparticle bands. This situation is reminiscent of Ce-based heavy-fermion systems, whose band structures are often very similar to those of non-4f La-based compounds. The narrow heavy quasiparticle bands are located just below the Fermi level (EF), and their band structure could not be resolved by the present energy resolution. We also showed that most of the U 5 f spectral weight exists not as the coherent heavy-fermion bands but as incoherent components that distribute over a wide energy range, spanning from near EF to approximately 2 eV. This result indicates that the heavy quasiparticle bands are enormously renormalized by the electron correlation effect. Additionally, we showed that the spectral intensity of the heavy-fermion bands is almost temperature independent, at least up to 100 K, where the magnetic susceptibility follows a Curie-Weiss behavior.