Probing the bright exciton state in twisted bilayer graphene via resonant Raman scattering

The band structure of bilayer graphene is tunable by introducing a relative twist angle between the two layers, unlocking exotic phases, such as superconductors and Mott insulators, providing fertile ground for new physics. At intermediate angles around 10°, highly degenerate electronic transitions hybridize to form excitonic states, quite unusual phenomenon in metallic system. We probe bright exciton mode using resonant Raman scattering measurements track evolution intensity G peak, corresponding E2g phonon. By cryogenically cooling sample, we are able resolve both incoming outgoing resonances peak function excitation energy, prominent manifestation serving state process. For sample with 8.6°, report weakly temperature dependent resonance broadening γ ≈ 0.07 eV. In limit small inhomogeneous broadening, observed places lower bound lifetime at 10 fs presence charges excitons excited light pulse measurement, limited rapid exciton–exciton exciton–charge graphene.