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Updated: Jun 23, 2025

Resonance Raman Spectroscopy of Extreme Nanowires and Other 1D Systems
Published on: April 28, 2016
A Resonance-Sensitive Ultralow-Frequency Raman Mode in Twisted Bilayer Graphene
Shuowen Yan1, Jianqi Huang2,3,4, He Hao1
1Center for Nanochemistry, Beijing Science and Engineering Center for Nanocarbons, Beijing National Laboratory for Molecular Sciences, College of Chemistry and Molecular Engineering, Peking University, 100871 Beijing, China.
Abstract:
Twisted bilayer graphene (tBLG) possesses intriguing physical properties including unconventional superconductivity, enhanced light-matter interaction due to the formation of van Hove singularities (vHS), and a divergence of density of states in the electronic band structures. The vHS energy band gap provides optical resonant transition channels that can be tuned by the twist angle and interlayer coupling. Raman spectroscopy provides rich information on the vHS structure of tBLG. Here, we report the discovery of an ultralow-frequency Raman mode at ∼49 cm-1 in tBLG. This mode is assigned to the combination of ZA (an out-of-plane acoustic phonon) and TA (a transverse acoustic phonon) phonons, and the Raman scattering is proposed to occur at the so-called mini-valley. This mode is found to be particularly sensitive to the change in vHS in tBLG. Our findings may deepen the understanding of Raman scattering in tBLG and help to reveal vHS-related electron-phonon interactions in tBLG.
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