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 ${\mathrm{UPt}}_{3}$. The overall band structure revealed by the present ARPES measurements is compared with density-functional calculations for ${\mathrm{UPt}}_{3}$ and the non-$5f$ reference compound ${\mathrm{ThPt}}_{3}$. We showed that the calculation for ${\mathrm{ThPt}}_{3}$ gives a better description of the experimental band structure, except for the $5f$-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 (${E}_{\mathrm{F}}$), and their band structure could not be resolved by the present energy resolution. We also showed that most of the U $5f$ spectral weight exists not as the coherent heavy-fermion bands but as incoherent components that distribute over a wide energy range, spanning from near ${E}_{\mathrm{F}}$ 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.