Title: Excitonic effects in third harmonic generation: the case of carbon nanotubes and nanoribbons,
Abstract: Linear and nonlinear optical properties of low dimensional nanostructures
have attracted a large interest in the scientific community as tools to probe
the strong confinement of the electrons and for possible applications in
optoelectronic devices. In particular it has been shown that the linear optical
response of carbon nanotubes [Science 308, 838 (2005)] and graphene nanoribbons
[Nat. Comm. 5, 4253 (2014)] is dominated by bounded electron-hole pairs, the
excitons. The role of excitons in linear response has been widely studied, but
still little is known on their effect on nonlinear susceptibilities. Using a
recently developed methodology [Phys. Rev. B 88, 235113 (2013)] based on
well-established ab-initio many-body perturbation theory approaches, we find
that quasiparticle shifts and excitonic effects significantly modify the
third-harmonic generation in carbon nanotubes and graphene nanoribbons. For
both systems the net effect of many-body effects is to reduce the intensity of
the main peak in the independent particle spectrum and redistribute the
spectral weight among several excitonic resonances.