Abstract
Significant excitonic effects were observed in graphene by measuring its optical conductivity in a broad spectral range including the two-dimensional -band saddle-point singularities in the electronic structure. The strong electron-hole interactions manifest themselves in an asymmetric resonance peaked at 4.62 eV, which is redshifted by nearly 600 meV from the value predicted by ab initio calculations for the band-to-band transitions. The observed excitonic resonance is explained within a phenomenological model as a Fano interference of a strongly coupled excitonic state and a band continuum. Our experiment also showed a weak dependence of the excitonic resonance in few-layer graphene on layer thickness. This result reflects the effective cancellation of the increasingly screened repulsive electron-electron () and attractive electron-hole () interactions.
- Received 19 October 2010
DOI:https://doi.org/10.1103/PhysRevLett.106.046401
© 2011 American Physical Society