Triplet excitations in graphene-based systems

Niels Bohr Institute, University of Copenhagen - Universitetsparken 5, 2100 Copenhagen, Denmark

^(a) posvyanskij@gmail.com

Received: 8 January 2015
Accepted: 9 February 2015

Abstract

In this paper we investigate the excitations in a single graphene layer and in a single-walled carbon nanotube, i.e. the spectrum of magnetic excitations is calculated. In the absence of interactions in these systems there is a unique gap in the electron-hole continuum. We show that in the presence of Coulomb correlations bound states, magnons, appear in this forbidden region. The Coulomb interaction is examined in the context of the Pariser-Parr-Pople (PPP) model which takes into account the long-range nature of the interaction. The energy of the new bound states depends on the strength of the Coulomb forces. The calculations are performed for arbitrary electron-hole momentum q. In the end, this work finally settles the discussion sabout the existence of triplet excitations in graphene which has been lasting for a decade in the literature.