Neutral triplet Collective Mode as a new decay channel in Graphite

TL;DR

This paper investigates a neutral triplet collective mode in graphene and graphite, showing it influences electron decay rates and spectral properties, and can explain previously missing decay components in experiments.

Contribution

It introduces a phenomenological Hamiltonian for electron-triplet boson interactions, extending the Holstein polaron model to include dispersive triplet modes in honeycomb lattices.

Findings

The neutral triplet mode affects electron spectral properties.

It accounts for part of the missing decay rate in graphite.

The model generalizes polaron theory to triplet bosons with dispersion.

Abstract

In an earlier work we predicted the existence of a neutral triplet collective mode in undoped graphene and graphite [Phys. Rev. Lett. {\bf 89} (2002) 16402]. In this work we study a phenomenological Hamiltonian describing the interaction of tight-binding electrons on honeycomb lattice with such a dispersive neutral triplet boson. Our Hamiltonian is a generalization of the Holstein polaron problem to the case of triplet bosons with non-trivial dispersion all over the Brillouin zone. This collective mode constitutes an important excitation branch which can contribute to the decay rate of the electronic excitations. The presence of such collective mode, modifies the spectral properties of electrons in graphite and undoped graphene. In particular such collective mode, as will be shown in this paper, can account for some part of the missing decay rate in a time-domain measurement done on graphite.