title: Optical-phonon resonances with saddle-point excitons in twisted-bilayer graphene.
abstract: Twisted-bilayer graphene (tBLG) exhibits van Hove singularities in the density of states that can be tuned by changing the twisting angle θ. A θ-defined tBLG has been produced and characterized with optical reflectivity and resonance Raman scattering. The θ-engineered optical response is shown to be consistent with persistent saddle-point excitons. Separate resonances with Stokes and anti-Stokes Raman scattering components can be achieved due to the sharpness of the two-dimensional saddle-point excitons, similar to what has been previously observed for one-dimensional carbon nanotubes. The excitation power dependence for the Stokes and anti-Stokes emissions indicate that the two processes are correlated and that they share the same phonon.
authors.affiliation: Photonics Laboratory, ETH Zürich , 8093 Zürich, Switzerland.
authors.forename: Ado
authors.initials: A
authors.lastname: Jorio
authors.forename: Mark
authors.initials: M
authors.lastname: Kasperczyk
authors.forename: Nick
authors.initials: N
authors.lastname: Clark
authors.forename: Elke
authors.initials: E
authors.lastname: Neu
authors.forename: Patrick
authors.initials: P
authors.lastname: Maletinsky
authors.forename: Aravind
authors.initials: A
authors.lastname: Vijayaraghavan
authors.forename: Lukas
authors.initials: L
authors.lastname: Novotny
keywords: Graphene; Raman scattering; coherence; optical reflectivity