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首页> 外文期刊>Physical review >Van Hove singularities in doped twisted graphene bilayers studied by scanning tunneling spectroscopy
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Van Hove singularities in doped twisted graphene bilayers studied by scanning tunneling spectroscopy

机译：扫描隧道光谱研究掺杂扭曲石墨烯双层中的Van Hove奇异性

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摘要

The effect of electron doping on the van Hove singularities (vHs) which develop in twisted graphene bilayers (tBLs) is studied for a broad range of rotation angles θ (1.5° ＜ θ ＜ 15°) by means of scanning tunneling microscopy and spectroscopy. Bilayer and trilayer graphene islands were grown on the 6H-SiC(000-1) (3 × 3) surface, which results in tBLs doped in the 10~(12) cm~(-2) range by charge transfer from the substrate. For large angles, doping manifests in a strong asymmetry of the positions of the upper (in empty states) and lower (in occupied states) vHs with respect to the Fermi level. The splitting of these vHs energies is found essentially independent of doping for the whole range of 9 values, but the center of theses vHs shifts towards negative energies with increasing electron doping. Consequently, the upper vHs crosses the Fermi level for smaller angles (around 3°). The analysis of the data performed using tight-binding calculations and simple electrostatic considerations shows that the interlayer bias remains small (＜ 100 mV) for the doping level resulting from the interfacial charge transfer (approx= 5 × 10~(12) cm~(-2)).
机译：通过扫描隧道显微镜和光谱学研究了电子掺杂对扭曲石墨烯双层（tBLs）中产生的van Hove奇异性（vHs）的影响，旋转角度θ（1.5°＜θ＜15°）的范围很广。双层和三层石墨烯岛生长在6H-SiC（000-1）（3×3）表面上，通过从基板进行电荷转移，导致tBL掺杂在10〜（12）cm〜（-2）范围内。对于大角度，掺杂表现为相对于费米能级的上部（在空状态）和下部（在占据状态）vHs的位置很不对称。发现这些vHs能量的分裂基本上与9个值整个范围内的掺杂无关，但是随着电子掺杂的增加，这些vHs的中心向负能量移动。因此，较高的vHs以较小的角度（约3°）穿过费米能级。使用紧密结合计算和简单的静电考虑对数据进行的分析表明，对于由界面电荷转移引起的掺杂水平（约= 5×10〜（12）cm〜（），层间偏压仍然很小（<100 mV）。 -2））。

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