  The state-of-the-art defect engineering techniques have paved the way to
realize novel quantum phases out of pristine materials. Here, through
density-functional calculations and model studies, we show that the chain-doped
monolayer transition metal dichalcogenides (TMDs), where M atoms on a single
the zigzag chains are replaced by a higher-valence transition-metal element
M$^\prime$ (MX$_2$/M$^\prime$), exhibit one-dimensional (1D) bands. These 1D
bands, occurring in the fundamental gap of the pristine material, are
dispersive along the doped chain but are strongly confined along the lateral
direction. This confinement occurs as the bare potential of the dopant chain
formed by the positively charged M$^\prime$ ions resembles the potential well
of a uniformly charged wire. These bands could show novel 1D physics, including
a new type of Tomonaga-Luttinger liquid behavior, multi-orbital Mott insulator
physics, and an unusual optical absorption, due to the simultaneous presence of
the spin-orbit coupling, strong correlation, multiple orbitals, Rashba spin
splitting, and broken symmetry. For the half-filled 1D bands, we find, quite
surprisingly, a broadening of the 1D bands due to correlation, as opposed to
the expected band narrowing. This is interpreted to be due to multiple orbitals
forming the single Hubbard band at different points of the Brillouin zone.
Furthermore, due to the presence of an intrinsic electric field along the
lateral direction, the 1D bands are Rashba spin-split and provide a new
mechanism for tuning the valley dependent optical transitions.
