  Two-dimensional (2D) moire systems based on twisted bilayer graphene and
transition metal dichalcogenides provide a promising platform to investigate
emergent phenomena driven by strong electron-electron interactions in
partially-filled flat bands1-11. A natural question arises: is it possible to
expand the 2D correlated moire physics to one-dimensional (1D)? This requires
selectively doping of 1D moire chain embedded in the 2D moire systems, which is
an outstanding challenge in experiment and seems to be not within the grasp of
today's technology. Therefore, an experimental demonstration of the 1D moire
chain with partially-filled flat bands remains absent. Here we show that we can
introduce 1D boundaries, separating two regions with different twist angles, in
twisted bilayer WSe2 (tWSe2) by using scanning tunneling microscopy (STM), and
demonstrate that the flat bands of moire sites along the 1D boundaries can be
selectively filled. The charge and discharge states of correlated moire
electrons in the 1D moire chain can be directly imaged and manipulated by
combining a back-gate voltage with the STM bias. Our results open the door for
realizing new correlated electronic states of the 1D moire chain in 2D systems.
