High-energy excitonic effects in single-layer graphene

Using high-energy polarization-dependent reflectivity, we discover high-energy resonant excitons at room temperature in single-layer graphene. The resonant excitons occur at ~10.04 and ~12.29 eV arising from transitions between parallel σ and π* states along Γ-K as well as σ and σ* states at the M point, respectively. The observation of spectral weight transfer signifies electronic corelation and that the two-dimensional nature and low-energy properties are strongly coupled with high-energy bands. Our result shows the importance of electron-electron and electron-hole interactions in determining electronic and optical properties of graphene and two-dimensional systems.