Table 1 Mean exciton diameters of the zero-momentum states \(| \varvec{0};+,+;0,m \rangle\) and \(| \varvec{0};-,-;0,-m \rangle\) as obtained with the Coulomb and Rytova–Keldysh potentials with \(\varepsilon _{s} = 6\) and \(\varepsilon _{d} = 28\). In the case of the Coulomb potential the radii must be compared to the film thickness, which is \(L_{z} = {6}\,{\hbox {nm}}\).

From: Single-particle properties of topological Wannier excitons in bismuth chalcogenide nanosheets