Resonance Raman Spectrum of Doped Epitaxial Graphene at the Lifshitz Transition.
Resonance Raman Spectrum of Doped Epitaxial Graphene at the Lifshitz Transition.
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DOI：
10.1021/acs.nanolett.8b02979
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发表时间：
2018-08
期刊：
影响因子：
10.8
通讯作者：
M. Hell;N. Ehlen;B. Senkovskiy;E. H. Hasdeo;A. Fedorov;Daniela Dombrowski;C. Busse;T. Michely
中科院分区：
文献类型：
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作者：
M. Hell;N. Ehlen;B. Senkovskiy;E. H. Hasdeo;A. Fedorov;Daniela Dombrowski;C. Busse;T. Michely
我们采用超高真空（UHV）拉曼光谱和角分辨光电子能谱（ARPES）研究了Ir（111）衬底上外延石墨烯的掺杂依赖的拉曼光谱。研究了载流子浓度为4.4 × 1014 cm-2时，从原始石墨烯到重铯掺杂石墨烯的拉曼光谱的演化。在这种掺杂下，石墨烯处于Lifshitz转变的开始，并且重整化效应降低了电子带宽。布里渊区中鞍点处的光学跃迁然后变得实验上可通过紫外（UV）光激发获得，其在联合态密度中的货车霍韦奇异性附近实现共振拉曼条件。完全掺杂的石墨烯/Ir（111）的拉曼G带的位置向下移动了1060 cm-1。Cs掺杂的外延石墨烯的G带不对称性呈现与绝缘体上的掺杂石墨烯的G带的不对称性相反的不寻常的强Fano不对称性。我们的计算可以充分解释这些观察衬底依赖的量子干涉效应的散射路径的振动和电子拉曼散射。
We employ ultra-high vacuum (UHV) Raman spectroscopy in tandem with angle-resolved photoemission (ARPES) to investigate the doping-dependent Raman spectrum of epitaxial graphene on Ir(111). The evolution of Raman spectra from pristine to heavily Cs doped graphene up to a carrier concentration of 4.4 × 1014 cm-2 is investigated. At this doping, graphene is at the onset of the Lifshitz transition and renormalization effects reduce the electronic bandwidth. The optical transition at the saddle point in the Brillouin zone then becomes experimentally accessible by ultraviolet (UV) light excitation, which achieves resonance Raman conditions in close vicinity to the van Hove singularity in the joint density of states. The position of the Raman G band of fully doped graphene/Ir(111) shifts down by ∼60 cm-1. The G band asymmetry of Cs doped epitaxial graphene assumes an unusual strong Fano asymmetry opposite to that of the G band of doped graphene on insulators. Our calculations can fully explain these observations by substrate dependent quantum interference effects in the scattering pathways for vibrational and electronic Raman scattering.