通过扩散型高密度片上掺杂实现单层石墨烯 Lifshitz 转变处的质量反转
Mass inversion at the Lifshitz transition in monolayer graphene by diffusive, high-density, on-chip, doping
AI总结：
针对传统输运测量装置无法兼容超高真空化学掺杂、场效应掺杂密度不足的问题，开发了扩散型碱金属蒸气片上掺杂方法，实现超高载流子掺杂并观测到石墨烯Lifshitz转变的回旋质量反转。
摘要：
电荷输运测量的实验装置通常与化学掺杂所需的超高真空条件不兼容，限制了输运方法可研究的载流子密度范围。包括介电栅极和离子液体栅极在内的场效应方法，所能达到的载流子密度过低，无法诱发电电子相变。为弥补这一差距，我们开发了一种集成倒装芯片方法，在扩散区域内通过碱金属蒸气对石墨烯进行掺杂，适用于超高载流子密度下的电荷输运测量。我们向填充有惰性气体的密封腔中引入铯液滴，通过铯原子在石墨烯表面的扩散、吸附和电离过程对单层石墨烯样品进行掺杂，借助原位霍尔测量监测到掺杂电子密度超过$4.7\times10^{14}~\text{cm}^{-2}$。该密封组件具有抗氧化稳定性，可开展不同温度和磁场下的电荷输运测量。我们通过霍尔效应观测到回旋质量反转，这一现象表明单层石墨烯双曲线M点处发生的Lifshitz转变伴随费米面几何结构的变化。透明石英衬底还可作为光学窗口，支持非共振拉曼散射测量。我们的研究结果表明，此前仅限于超高真空环境的化学掺杂，可在常压惰性气体环境的扩散区域中应用，从而支持标准低温环境下的电荷输运研究。
英文摘要：
Experimental setups for charge transport measurements are typically not compatible with the ultra-high vacuum conditions for chemical doping, limiting the charge carrier density that can be investigated by transport methods. Field-effect methods, including dielectric gating and ionic liquid gating, achieve too low a carrier density to induce electronic phase transitions. To bridge this gap, we developed an integrated flip-chip method to dope graphene by alkali vapour in the diffusive regime, suitable for charge transport measurements at ultra-high charge carrier density. We introduce a cesium droplet into a sealed cavity filled with inert gas to dope a monolayer graphene sample by the process of cesium atom diffusion, adsorption and ionization at the graphene surface, with doping beyond an electron density of $4.7\times10^{14}~\mathrm{cm}^{-2}$ monitored by operando Hall measurement. The sealed assembly is stable against oxidation, enabling measurement of charge transport versus temperature and magnetic field. Cyclotron mass inversion is observed via the Hall effect, indicative of the change of Fermi surface geometry associated with the Liftshitz transition at the hyperbolic $M$ point of monolayer graphene. The transparent quartz substrate also functions as an optical window, enabling non-resonant Raman scattering. Our findings show that chemical doping, hitherto restricted to ultra-high vacuum, can be applied in a diffusive regime at ambient pressure in an inert gas environment and thus enable charge transport studies in standard cryogenic environments
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