Eur. Phys. J. B (2012) 85: 395
https://doi.org/10.1140/epjb/e2012-30593-0

Regular Article

Wannier excitons signalling strong Coulomb coupling in graphene

¹ Department of Physics and Material Sciences Center, Philipps University Marburg, Renthof 5, 35032 Marburg, Germany
² Department of Physics, Åbo Akademi University, 20500 Turku, Finland

^a e-mail: johagron@abo.fi

Received: 13 July 2012
Received in final form: 24 September 2012
Published online: 3 December 2012

Abstract

The Wannier equation for quasiparticles with a linear dispersion is investigated. It is shown that Coulomb bound compounds of mass less electron-hole pairs can only exist if the effective coupling strength exceeds the critical value of approximately 0.46. At the critical value, a second-order transition to a weak Coulomb regime is found. It is shown that the existence of bound excitons indicates an instability of the noninteracting ground state.