Van Hove Singularity-Enhanced\nRaman Scattering and\nPhotocurrent Generation in Twisted Monolayer–Bilayer Graphene

Twisted monolayer–bilayer graphene (TMBG) has\nrecently emerged\nas an exciting platform for exploring correlated physics and topological\nstates with rich tunability. Strong light–matter interaction\nwas realized in twisted bilayer graphene, boosting the development\nof broadband graphene photodetectors from the visible to infrared\nspectrum with high responsivity. Extending this approach to the case\nof TMBG will help design advanced quantum nano-optoelectronic devices\nbecause of the reduced symmetry of the system. Here, we observe the\nformation of van Hove singularities (VHSs) in TMBG by monitoring the\nsignificant enhancement of the Raman intensity of the G peak and the\nintensity ratio of G and 2D peaks. The strong interlayer coupling\nalso leads to the appearance of twist-angle-dependent Raman R and\nR′ peaks in TMBG. Furthermore, the constructed graphene photodetectors\nfrom 13.5°-TMBG show significantly enhanced photoresponsivity\n(∼31 folds of monolayer graphene and ∼15 folds of trilayer\ngraphene) when the energy of incident photons matches the interval\nenergy between the two VHSs in the conduction and valence bands. Our\nfindings establish TMBG as a tunable platform for investigating the\nlight–matter interaction and designing high-performance graphene\nphotodetectors with combined high responsivity and high selectivity.