Direct observation of dispersive Kondo resonance peaks in a heavy-fermion system

Im, H. J.*; Ito, Takahiro*; Kim, H.-D.*; Kimura, Shinichi*; Lee, K. E.*; Hong, J. B.*; Kwon, Y. S.*; Yasui, Akira; Yamagami, Hiroshi

Ce 4-4 resonant angle-resolved photoemission spectroscopy was carried out to study the electronic structure of strongly correlated Ce 4 electrons in a quasi-two-dimensional nonmagnetic heavy-fermion system CeCoGeSi. For the first time, dispersive coherent peaks of an state crossing the Fermi level, the so-called Kondo resonance, are directly observed together with the hybridized conduction band. Moreover, the experimental band dispersion is quantitatively in good agreement with a simple hybridization-band picture based on the periodic Anderson model. The obtained physical quantities, i.e., coherent temperature, Kondo temperature, and mass enhancement, are comparable to the results of thermodynamic measurements. These results manifest an itinerant nature of Ce 4 electrons in heavy-fermion systems and clarify their microscopic hybridization mechanism.