Triplet excitations in graphene-based systems

TL;DR

This paper explores how Coulomb interactions induce magnon excitations within the electron-hole continuum in graphene and carbon nanotubes, revealing their dispersion, effective mass, and conditions for existence.

Contribution

It introduces a detailed analysis of magnon excitations in graphene-based systems considering long-range Coulomb interactions using the PPP model, highlighting their properties and existence conditions.

Findings

Magnons appear in the forbidden electron-hole gap due to Coulomb correlations.

The dispersion law, effective mass, and velocity of magnons are calculated.

Critical parameters for the existence of magnons are identified.

Abstract

In this article 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 new states, magnons, appear in this forbidden region. Coulomb interaction is examined in the context of Pariser-Parr-Pople (PPP) model which takes into account long range nature of interaction. The energy of new bound states depends on the strength of Coulomb forces. The calculations are performed for arbitrary electron-hole ($e-h$) momentum $\textbf{q}$ what allows to find the magnons dispersion law $\varepsilon(\textbf{q})$, effective mass $m^*$ and velocity $v_{gr}$. Finally, we determine the critical values of system parameters when this type of excitations can exist.