  The 4f-electron delocalization plays a key role in the low-temperature
properties of rare-earth metals and intermetallics, including heavy fermions
and mix-valent compounds, and is normally realized by the many-body Kondo
coupling between 4f and conduction electrons. Due to the large onsite Coulomb
repulsion of 4f electrons, the bandwidth-control Mott-type delocalization,
commonly observed in d-electron systems, is difficult in 4f-electron systems
and remains elusive in spectroscopic experiments. Here we demonstrate that the
bandwidth-control orbital-selective delocalization of 4f electrons can be
realized in epitaxial Ce films by thermal annealing, which results in a
metastable surface phase with a reduced layer spacing. The resulting
quasiparticle bands exhibit large dispersion with exclusive 4f character near
E_F and extend reasonably far below the Fermi energy, which can be explained
from the Mott physics. The experimental quasiparticle dispersion agrees
surprisingly well with density-functional theory calculation and also exhibits
unusual temperature dependence, which could be a direct consequence of the
delicate interplay between the bandwidth-control Mott physics and the
coexisting Kondo hybridization. Our work therefore opens up the opportunity to
study the interaction between two well-known localization-delocalization
mechanisms in correlation physics, i.e., Kondo vs Mott, which can be important
for a fundamental understanding of 4f-electron systems.
