  Motivated by recent experiments demonstrating intricate quantum Hall physics
on the surface of elemental bismuth, we consider proximity coupling an $s$-wave
superconductor to a two-dimensional electron gas with strong Rashba spin-orbit
interactions in the presence of a strong perpendicular magnetic field. We focus
on the high-field limit so that the superconductivity can be treated as a
perturbation to the low-lying Landau levels. In the clean case, wherein the
superconducting order parameter takes the form of an Abrikosov vortex lattice,
we show that a lattice of hybridized Majorana modes emerges near the plateau
transition of the lowest Landau level. However, unless
magnetic-symmetry-violating perturbations are present, the system always has an
even number of chiral Majorana edge modes and thus is strictly speaking Abelian
in nature, in agreement with previous work on related setups. Interestingly,
however, a weak topological superconducting phase can very naturally be
stabilized near the plateau transition for the square vortex lattice. The
relevance of our findings to potential near-term experiments on proximitized
materials such as bismuth will be discussed.
