Excitons in Graphene and the Influence of the Dielectric Environment

TL;DR

This paper investigates how the dielectric environment affects exciton properties in graphene, revealing a transition from strong to weak Coulomb effects and the disappearance of bound states on high-permittivity substrates.

Contribution

It provides a detailed analysis of exciton behavior in graphene under varying dielectric conditions, identifying a critical transition point and the impact of substrates.

Findings

Freestanding graphene has exciton binding energies over 3 eV.

A second-order transition occurs at a critical dielectric constant.

Bound exciton states vanish on high-permittivity substrates like SiC.

Abstract

The exciton Wannier equation for graphene is solved for different background dielectric constants. It is shown that freestanding graphene features strong Coulomb effects with a very large exciton binding energy exceeding $3\,$eV. A second-order transition to a weak Coulomb regime is found if the effective background dielectric constant exceeds a critical value. All bound-state solutions vanish for epitaxial graphene on a substrate with large background permittivity, such as SiC.