  Synchrotron-based angle-resolved photoemission spectroscopy was employed to
investigate the temperature evolution of the Yb 4f spectral for surface and
bulk in the Kondo lattice YbCu$_2$Si$_2$.Our study quantitatively distinguishes
between the surface and bulk hybridization processes, revealing that the onset
temperatures for both surface and bulk hybridization processes are
significantly higher than the Kondo temperature. Additionally, we found that
the effective surface Kondo temperature is much lower than that of the bulk.
These findings offer valuable insights into the understanding of heavy fermion
physics.
