Attractive Coulomb interaction of 2D Rydberg excitons

TL;DR

This paper theoretically investigates Coulomb interactions of highly excited 2D Rydberg excitons, revealing attractive exchange interactions and long-range van der Waals forces, which could enhance optical nonlinearity in 2D materials.

Contribution

It demonstrates that excited 2D excitons exhibit attractive exchange interactions and van der Waals long-range forces, expanding understanding of excitonic interactions in 2D systems.

Findings

Exchange interaction becomes attractive for excited excitons

Long-range van der Waals interaction is present in 2D Rydberg excitons

Interaction strength scales linearly with principal quantum number

Abstract

We analyze theoretically the Coulomb scattering processes of highly excited excitons in the direct bandgap semiconductor quantum wells. We find that contrary to the interaction of ground state excitons the electron and hole exchange interaction between excited excitons has an attractive character both for $s$- and $p$-type 2D excitons. Moreover, we show that similarly to the three-dimensional (3D) highly excited excitons, the direct interaction of 2D Rydberg excitons exhibits van der Waals type long-range interaction. The results predict the linear growth of the absolute value of exchange interaction strength with an exciton principal quantum number, and point the way towards enhancement of optical nonlinearity in 2D excitonic systems.