  The low in-plane symmetry in layered 1T'-ReS$_2$ results in strong band
anisotropy, while its manifestation in the electronic properties is challenging
to resolve due to the lack of effective approaches for controlling the local
current path. In this work, we reveal the giant transport anisotropy in
monolayer to four-layer ReS$_2$ by creating directional conducting paths via
nanoscale ferroelectric control. By reversing the polarization of a
ferroelectric polymer top layer, we induce conductivity switching ratio of
>1.5x10$^8$ in the ReS$_2$ channel at 300 K. Characterizing the domain-defined
conducting nanowires in an insulating background shows that the conductivity
ratio between the directions along and perpendicular to the Re-chain can exceed
7.9x10$^4$. Theoretical modeling points to the band origin of the transport
anomaly, and further reveals the emergence of a flat band in few-layer ReS$_2$.
Our work paves the path for implementing the highly anisotropic 2D materials
for designing novel collective phenomena and electron lensing applications.
