Large excitonic effect on van der Waals interaction between two-dimensional semiconductors

An exceptionally large excitonic effect on the van der Waals (vdW) interaction between two-dimensional semiconductors is unraveled using the Lifshitz theory in conjunction with the ab initio GW plus Bethe-Salpeter equation formalism. Upon consideration of the electron-hole interaction, the vdW energy between two atomistic layers separated by 10 000 angstroms can be larger by a ratio of ∼30%, which is an order of magnitude greater than that seen for semi-infinite silicon surfaces. The large influence of the short-range electron-hole interaction on the long-range effect of quantum fluctuations is rooted in the ultra-thin nature of two-dimensional semiconductors which results in not only large exciton binding energy but also amplified roles of low-frequency dielectric responses.