  The interplay between electron-electron interactions and structural ordering
can yield exceptionally rich correlated electronic phases. We have used
scanning tunneling microscopy to investigate bulk 1T-TaSe2 and have uncovered
surprisingly diverse correlated surface states thereof. These surface states
exhibit the same in-plane charge density wave ordering but dramatically
different electronic ground states ranging from insulating to metallic. The
insulating variety of surface state shows signatures of a decoupled surface
Mott layer. The metallic surface states, on the other hand, exhibit zero-bias
peaks of varying strength that suggest Kondo phases arising from coupling
between the Mott surface layer and the metallic bulk of 1T-TaSe2. The surface
of bulk 1T-TaSe2 thus constitutes a rare realization of the periodic Anderson
model covering a wide parameter regime, thereby providing a model system for
accessing different correlated phenomena in the same crystal. Our results
highlight the central role played by strong correlations in this material
family.
