Electron confinement in chain-doped transition metal dichalcogenides: A platform for spin-orbit coupled one-dimensional physics

State-of-the-art defect engineering techniques have paved the way to realize unique quantum phases out of pristine materials. Here, through density-functional calculations and model studies, we show that the chain-doped monolayer transition metal dichalcogenides, where $M$ atoms on a single zigzag chain are replaced by a higher-valence transition-metal element ${M}^{\ensuremath{'}}$ ($M{X}_{2}/{M}^{\ensuremath{'}}$), 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 ${M}^{\ensuremath{'}}$ ions resembles the potential well of a uniformly charged wire. These bands could show unique 1D physics, including another type of Tomonaga-Luttinger liquid behavior, multiorbital 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. We find the broadening of the half-filled 1D bands with correlation. It is surprising since correlation reduces the effective hopping interactions and in turn reduces the bandwidth. 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 mechanism for tuning the valley-dependent optical transitions.