Counting the Number of Bound States of Two-dimensional Screened Coulomb Potentials: A Semiclassical Approach

Portnoi and Galbraith recently proposed a beautiful and intriguing relationship defining the critical screening lengths associated with the apparition of new bound states for the two-dimensional statically screened Coulomb potential. Not only does semiclassical quantum theory show that this relationship is unfortunately not strictly exact, it has also proved helpful in the search for a potential which exactly verifies Portnoi and Galbraith's formula, namely $\frac{-e^2}{r (1+r/r_s)^2}$. The analytical eigenfunctions of the corresponding Schr\"{o}dinger equation at zero energy, when localized, lead to approximate upper bounds for critical screening lengths of the two-dimensional statically screened Coulomb potential.