Anomalies in G and 2D Raman Modes of Twisted Bilayer Graphene Near the Magic Angle

Abstract

The role of twist angle (${\theta }_t$) in tailoring the physical properties of heterostructures is emerging as a new paradigm in two-dimensional materials. The influence of flat electronic bands near the magic angle ($\sim$1.1${}^{\circ }$) on the phononic properties of twisted bilayer graphene (t-BLG) is not well understood. In this work, we systematically investigate the G and 2D Raman modes of t-BLG samples with twist angles ranging from $\sim$0.3${}^{\circ }$ to $\sim$3${}^{\circ }$ using micro-Raman spectroscopy. A key finding of our work is the splitting of the G mode near the magic angle due to moiré potential induced phonon hybridization. The linewidth of the low-frequency component of the G mode (G${}^{-}$), as well as the main component of the 2D mode, exhibits enhanced broadening near the magic angle due to increased electron-phonon coupling, driven by the emergence of flat electronic bands. Additionally, temperature-dependent Raman measurements (6-300 K) of magic-angle twisted bilayer graphene sample (${\theta }_t\sim$ 1${}^{\circ }$) reveal an almost tenfold increase in phonon anharmonicity-induced temperature variation in both components of the split G mode, as compared to Bernal-stacked bilayer graphene sample, further emphasizing the role of phonon hybridization in this system. These studies could be important for understanding the thermal properties of the twisted bilayer graphene systems.

Phys. Rev. B - Accepted on 16th June, 2025 [https://doi.org/10.1103/9xym-n83q]; 13 pages, 12 figures

References in corpus (13)

• 2D materials and van der Waals heterostructures
• Boron nitride substrates for high-quality graphene electronics
• Unconventional quantum Hall effect and Berry's phase of 2pi in bilayer graphene
• STM Spectroscopy of ultra-flat graphene on hexagonal boron nitride
• Universal mechanical exfoliation of large-area 2D crystals
• Lattice relaxation and energy band modulation in twisted bilayer graphenes
• Phonon anharmonicities in graphite and graphene
• Quantum Hall effect and Landau level crossing of Dirac fermions in trilayer graphene
• Imaging moiré deformation and dynamics in twisted bilayer graphene
• Heterostrain rules the flat-bands in magic-angle twisted graphene layers
• Optical Phonons in Twisted Bilayer Graphene with Gate-Induced Asymmetric Doping
• Raman spectra of twisted bilayer graphene close to the magic angle
• Phonon Linewidths in Twisted Bilayer Graphene near Magic Angle