High-resolution photoemission spectroscopy of CeNiGe₂ and CeCoGe₂

We have performed the high-resolution photoemission spectroscopy on the isostructural heavy fermion compounds, CeCoGe₂ and CeNiGe₂, as the representative samples of CeNi_{1 - x} Co_x Ge₂ to investigate the origin of the wide Ce 4f characters from the magnetic ( x = 0) to non-magnetic regime ( x = 1) via the quantum critical point ( x = 0.3). We directly observed a Kondo peak, whose width corresponds to the Kondo temperature, in both materials but the crystal field splitting only in CeNiGe₂. Both the Kondo temperature and the crystal field splitting are concluded to be affected by the hybridization between Ce 4f and Ni/Co 3d states.