  The paradigm of electrons interacting with a periodic lattice potential is
central to solid-state physics. Semiconductor heterostructures and ultracold
neutral atomic lattices capture many of the essential properties of 1D
electronic systems. However, fully one-dimensional superlattices are highly
challenging to fabricate in the solid state due to the inherently small length
scales involved. Conductive atomic-force microscope (c-AFM) lithography has
recently been demonstrated to create ballistic few-mode electron waveguides
with highly quantized conductance and strongly attractive electron-electron
interactions. Here we show that artificial Kronig-Penney-like superlattice
potentials can be imposed on such waveguides, introducing a new superlattice
spacing that can be made comparable to the mean separation between electrons.
The imposed superlattice potential "fractures" the electronic subbands into a
manifold of new subbands with magnetically-tunable fractional conductance (in
units of $e^2/h$). The lowest $G=2e^2/h$ plateau, associated with ballistic
transport of spin-singlet electron pairs, is stable against de-pairing up to
the highest magnetic fields explored ($|B|=16$ T). A 1D model of the system
suggests that an engineered spin-orbit interaction in the superlattice
contributes to the enhanced pairing observed in the devices. These findings
represent an important advance in the ability to design new families of quantum
materials with emergent properties, and mark a milestone in the development of
a solid-state 1D quantum simulation platform.
