Mohapatra A, Poudyal S, Ramachandra Rao M S, Jaiswal Manu
Graphene and 2D Systems Laboratory, Department of Physics, Indian Institute of Technology Madras, Chennai 600036, India.
Nano Functional Materials Technology Centre and Materials Science Research Centre, Department of Physics, Indian Institute of Technology Madras, Chennai 600036, India.
J Phys Condens Matter. 2024 Feb 23;36(20). doi: 10.1088/1361-648X/ad2887.
Turbostratic multilayer graphene presents a unique system with a large number of twisted interfaces with variable twist angles. In this work, we have systematically studied the laser excitation energy dependence of the Raman modes of turbostratic graphene. The combination of 4 different laser energies is shown to be important to reveal the twist angles ranging from 5to 30present at the same lateral position of the sample. Rotational or R-modes and D-like modes are observed, which directly arise from additional momentum transfer from the potential of corresponding superlattices. Trends in their dispersion and intensity are discussed. The resonant window for laser excitation indicates lowered positions of the van Hove singularities. Furthermore, an anomalous broadening factor of 0.17-0.265 eV is estimated for the resonance window when compared to the literature on isolated twisted bilayer graphene. Interestingly, a weak dependence of the R-modes on the laser wavelength is also observed. Finally, the dispersion of the 2D modes is also presented.
涡轮层状多层石墨烯呈现出一个独特的系统，具有大量扭转角可变的扭曲界面。在这项工作中，我们系统地研究了涡轮层状石墨烯拉曼模式的激光激发能量依赖性。结果表明，4种不同激光能量的组合对于揭示样品同一横向位置存在的5°至30°的扭转角很重要。观察到了旋转或R模式以及类D模式，它们直接源于相应超晶格势的额外动量转移。讨论了它们的色散和强度趋势。激光激发的共振窗口表明范霍夫奇点的位置降低。此外，与关于孤立扭曲双层石墨烯的文献相比，共振窗口的反常展宽因子估计为0.17 - 0.265电子伏特。有趣的是，还观察到R模式对激光波长的弱依赖性。最后，还给出了二维模式的色散情况。
