Many-body effects in Graphene

Isotope substitution of has been used to explore the electron-phonon interaction effects in the electronic structure [Bisti2021]. To do that, Li-doped quasi-freestanding graphene on Au/Ni(0001) surface has been investigated by means of isotope ($^{13}C$) substitution and angle-resolved photoemission spectroscopy. The well documented kink located at $169$ $meV$ from the Fermi level in the graphene made of $^{12}C$ atoms shifts to $162$ $meV$ once the carbon monolayer is composed by $^{13}C$ isotope. Such an energy shift is in excellent agreement with the expected softening of the phonon energy distribution due to the isotope substitution. Apart from providing an indisputable experimental proof of the electron-phonon coupling origin of this kink, the study demonstrates the experimental accuracy which can be achieved with a proper robust analysis framework applied to the experimental data.

For the investigation of the apparent band flattening [Jugovac2022], Li-doped quasi-freestanding graphene on Co(0001) surface has been considered, because of the absence of graphene band hybridization with the substrate, the doping contribution well represented by a rigid energy shift and the excellent electron-electron interaction screening ensured by the metallic substrate. A clear ARPES signal is detected along the $M$ point of the graphene Brillouin zone, giving rise to an apparent flattened band. By simulating the graphene spectral function from the density functional theory calculated bands, we demonstrate that the photoemission signal along the $M$ point originates from the spectral function tail of the unoccupied band above the Fermi level. Such interpretation put forward the absence of any additional strong correlation effects at the van-Hove singularity proximity, reconciling the mean field description of the graphene band structure even in the highly doped scenario.