Optical conductivity renormalization of graphene on SrTiO3 due to resonant excitonic effects mediated by Ti 3d orbitals

We present evidence of a drastic renormalization of the optical conductivity of graphene on SrTiO3 resulting in almost full transparency in the ultraviolet region. These findings are attributed to resonant excitonic effects further supported by ab initio Bethe-Salpeter equation and density functional theory calculations. The (?,?*) orbitals of graphene and Ti-3d t2g orbitals of SrTiO3 are strongly hybridized and the interactions of electron-hole states residing in those orbitals play dominant role in the graphene optical conductivity. These interactions are present much below the optical band gap of bulk SrTiO3. These results open a possibility of manipulating interaction strengths in graphene via d orbitals, which could be crucial for optical applications.