At very high doping levels the van Hove singularity in the ${\pi }^{*}$ band of graphene becomes occupied and exotic ground states possibly emerge, driven by many-body interactions. Employing a combination of ytterbium intercalation and potassium adsorption, we $n$ dope epitaxial graphene on silicon carbide past the ${\pi }^{*}$ van Hove singularity, up to a charge carrier density of $5.5\times {10}^{14}{\mathrm{cm}}^{-2}$. This regime marks the unambiguous completion of a Lifshitz transition in which the Fermi surface topology has evolved from two electron pockets into a giant hole pocket. Angle-resolved photoelectron spectroscopy confirms these changes to be driven by electronic structure renormalizations rather than a rigid band shift. Our results open up the previously unreachable beyond-van-Hove regime in the phase diagram of epitaxial graphene, thereby accessing an unexplored landscape of potential exotic phases in this prototype two-dimensional material.

中文翻译：

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超出范霍夫奇异性的石墨烯掺杂

在很高的掺杂水平下，van Hove的奇异性 ${\pi }^{*}$在多体相互作用的驱动下，石墨烯带占据并且可能出现奇异的基态。结合y嵌入和钾吸附，我们$ñ$ 掺杂碳化硅外延石墨烯 ${\pi }^{*}$ van Hove奇点，电荷载流子密度为 $5.5\times {10}^{14}{\mathrm{厘米}}^{-2}$。这种状态标志着Lifshitz过渡的明确完成，其中费米表面拓扑已从两个电子腔演化为一个巨大的空穴腔。角度分辨光电子能谱证实了这些变化是由电子结构的重新归一化驱动的，而不是由刚性带位移驱动的。我们的研究结果在外延石墨烯的相图中打开了以前无法达到的超出范霍夫的范围，从而获得了该原型二维材料中潜在的奇异相的未探索景观。