Simulating critical anion chemistry with indirect excitons

We study the effect of geometric constraints on the formation of indirect excitonic complexes with excess charge by considering the problem of two identical electrons moving in half-space subject to mutual Coulomb repulsion and the Coulomb attraction to a heavy hole of charge $Z$ residing on a flat impenetrable surface. We find that $Z=1$ is the critical charge necessary for binding, as compared to $Z_c\approx0.911$ in the unconstrained system. This suggests that interlayer electron--hole systems may serve as a flexible and experimentally accessible platform to study electronic behavior close to the critical nuclear charge necessary for binding.