  We show that hexagonal boron nitride (hBN), a two-dimensional insulator, when
subjected to an external superlattice potential forms a new paradigm for
electrostatically tunable excitons in the near- and mid-ultraviolet (UV). The
imposed potential has three consequences: (i) it renormalizes the effective
mass tensor, leading to anisotropic effective masses; (ii) it renormalizes the
band gap, eventually reducing it; (iii) it reduces the exciton binding
energies. All these consequences depend on a single dimensionless parameter,
which includes the product of strength of the external potential with its
period. In addition to the excitonic energy levels, we compute the optical
conductivity along two orthogonal directions, and from it the absorption
spectrum. The results for the latter show that our system is able to mimic a
grid polarizer. These characteristics make one-dimensional hBN superlattices a
viable and unexplored platform for fine-tuned polaritonics in the UV to visible
spectral range.
