  Angle-resolved photoelectron spectroscopy in the Ce 3d-4f excitation region
was measured for the paramagnetic state of CeRu2Si2, CeRu2(Si0.82Ge0.18)2, and
LaRu2Si2 to investigate the changes of the 4$f$ electron Fermi surfaces around
the quantum critical point. While the difference of the Fermi surfaces between
CeRu2Si2 and LaRu2Si2 was experimentally confirmed, a strong 4f-electron
character was observed in the band structures and the Fermi surfaces of
CeRu2Si2 and CeRu2(Si0.82Ge0.18)2, consequently indicating a delocalized nature
of the 4$f$ electrons in both compounds. The absence of Fermi surface
reconstruction across the critical composition suggests that SDW quantum
criticality is more appropriate than local quantum criticality in
CeRu2(Si[1-x]Ge[x])2.
