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arXiv 2107.09090cond-mat.mes-hall
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基于位移电流响应的扭曲双层石墨烯量子几何和电子-电子相互作用研究

Shift-current response as a probe of quantum geometry and electron-electron interactions in twisted bilayer graphene

Swati Chaudhary, Cyprian Lewandowski, Gil Refael

摘要:

莫尔材料,特别是扭曲双层石墨烯(TBG),表现出一系列迷人的现象,这些现象来自能带拓扑结构和相互作用的相互作用。我们发现,非线性二阶光响应是一个有吸引力的探测这种丰富的相互作用。光响应的主要部分是漂移电流,其由电子波函数和载流子性质的几何形状决定,因此通过电子-电子相互作用而变得强烈地改变。我们分析了其依赖于扭转角和掺杂,并调查的相互作用的作用。在没有相互作用的情况下,系统的响应由两个能量尺度决定:空穴和电子平带之间直接跃迁的平均能量,以及平带和色散带之间的间隙。包括电子-电子相互作用,两者都增强了非相互作用特征频率的响应,并产生新的共振。我们将这些变化归因于TBG中的填充相关能带重整化。我们的研究结果突出了TBG的非平凡几何性质与其光学响应之间的联系,并展示了光学探针如何访问moirene材料中相互作用的作用。

英文摘要:

Moiré materials, and in particular twisted bilayer graphene (TBG), exhibit a range of fascinating phenomena, that emerge from the interplay of band topology and interactions. We show that the non-linear second-order photoresponse is an appealing probe of this rich interplay. A dominant part of the photoresponse is the shift-current, which is determined by the geometry of the electronic wavefunctions and carrier properties, and thus becomes strongly modified by electron-electron interactions. We analyze its dependence on the twist angle and doping, and investigate the role of interactions. In the absence of interactions, the response of the system is dictated by two energy scales: the mean energy of direct transitions between the hole and electron flat bands, and the gap between flat and dispersive bands. Including electron-electron interactions, both enhance the response at the non-interacting characteristic frequencies as well as produce new resonances. We attribute these changes to the filling-dependent band renormalization in TBG. Our results highlight the connection between non-trivial geometric properties of TBG and its optical response, as well as demonstrate how optical probes can access the role of interactions in moiŕe materials.

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