Electron-hybridization phenomena in ${\mathrm{YbRh}}_2{\mathrm{Si}}_2$ were probed by angle-resolved photoemission. It was shown that the Yb $4f$–Rh $4d$ hybridization strength in the surface region of this heavy-fermion material can be varied by deposition of Ag. Site-specific charge transfer from adatoms leads to change of the energy overlap of the interacting states close to the Fermi energy. Our study demonstrates a new way to tune the hybridization between $4f$ and valence electrons as well as the induced strong correlation effects at the surface of heavy-fermion systems.

• Received 18 April 2009

DOI:https://doi.org/10.1103/PhysRevLett.103.137601