  Mott insulating behavior is induced by strong electron correlation and can
lead to exotic states of matter such as unconventional superconductivity and
quantum spin liquids. Recent advances in van der Waals material synthesis
enable the exploration of novel Mott systems in the two-dimensional limit. Here
we report characterization of the local electronic properties of single- and
few-layer 1T-TaSe2 via spatial- and momentum-resolved spectroscopy involving
scanning tunneling microscopy and angle-resolved photoemission. Our combined
experimental and theoretical study indicates that electron correlation induces
a robust Mott insulator state in single-layer 1T-TaSe2 that is accompanied by
novel orbital texture. Inclusion of interlayer coupling weakens the insulating
phase in 1T-TaSe2, as seen by strong reduction of its energy gap and quenching
of its correlation-driven orbital texture in bilayer and trilayer 1T-TaSe2. Our
results establish single-layer 1T-TaSe2 as a useful new platform for
investigating strong correlation physics in two dimensions.
