Influence of the wavefunction distribution on exciton dissociation in electric field

We show that the dissociation threshold of an exciton, a bound electron-hole pair, by an electric field is mainly determined by its energy: as expected, the dissociation voltage decreases with increasing exciton energy. However, within the multiplet of states belonging to a particular principal quantum number n , the dissociation voltage rises with increasing state energy, in contrast to the expectations based on energy arguments. This behavior is demonstrated for the yellow exciton states of Cu$_{2}$O and is attributed to the distribution of the wavefunction in the potential landscape, where the lower (higher) lying state in the multiplet is shifted away (towards) the tunnel barrier.