Strongly renormalized quasiparticles in UPt

UPtにおける強く繰り込まれた準粒子

藤森 伸一   ; 竹田 幸治   ; 山上 浩志; 山本 悦嗣  ; 芳賀 芳範   ; 川崎 郁斗  

Fujimori, Shinichi; Takeda, Yukiharu; Yamagami, Hiroshi; Yamamoto, Etsuji; Haga, Yoshinori; Kawasaki, Ikuto

UPt shows a superconducting transition at Tc = 0.5 K, and the superconducting state has multiple phases in the magnetic-field and temperature plane, revealing the presence of multiple superconducting order parameters. The above superconducting state is formed by heavy quasiparticles. In this study, we performed angle-resolved photoemission (ARPES) experiments using soft X rays to investigate the electronic structure of the heavy-fermion superconductor UPt. The overall band structure revealed by the present ARPES measurements is compared with density-functional calculations for UPt and the non-5f reference compound ThPt. We showed that the calculation for ThPt gives a better description of ARPES results except for heavy quasiparticle bands at the Fermi level (EF). In addition, we extracted the U 5f spectral weight by utilizing photo energy dependence on the photoemission cross-section. In the soft X-ray range, the U 5f and Pt 5d orbitals have dominant contributions, and the relative photoemission cross-section ratio decreases with increasing photon energy, and therefore, we can extract the U 5f component by comparing the spectra measured at different photon energies. Figure 1 shows the ARPES spectra at the high-symmetry points measured at two different photon energies. The difference curves reflect the U 5f spectral function. The narrow peak located at EF, whose bandwidth is narrower than the present energy resolution, is the coherent heavy quasiparticle component. The difference curves in Fig. 1 revealed that most of the U 5f spectral weight exist not as the coherent heavy fermion bands but as incoherent components which distribute over a wide energy range from near EF region to 2 eV. Therefore, this result shows that the heavy quasiparticle bands are enormously renormalized by the electron correlation effect and is consistent with the reported heavy fermion behavior.