Attractive electron-electron interactions from internal screening in magic-angle twisted bilayer graphene
Attractive electron-electron interactions from internal screening in magic-angle twisted bilayer graphene
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DOI：
10.1103/physrevb.100.235424
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发表时间：
2019-12-12
影响因子：
3.7
通讯作者：
Lischner, Johannes
中科院分区：
文献类型：
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作者：
Goodwin, Zachary A. H.;Corsetti, Fabiano;Lischner, Johannes
扭曲双层石墨烯（tBLG）最近成为研究电子相关性的新平台，其强度可以通过扭曲角控制。在这里，我们研究了内部屏蔽对未掺杂 tBLG 中电子-电子相互作用的影响。使用随机相位近似，我们发现 tBLG 的介电响应在魔角附近急剧增加，并且高度依赖于扭转角。由于费米速度作为波矢量函数的突然变化，真实空间中的屏蔽相互作用对于魔角附近的某些扭转角表现出有吸引力的区域。吸引相互作用可以诱发电荷密度波和超导性，因此我们的发现可能有助于理解最近在未掺杂 tBLG 中观察到的强相关现象的微观起源。由此产生的筛选哈伯德参数大大减少，并表现出对扭转角的非线性依赖性。我们还使用约束随机相位近似进行计算，并对扭转角相关的 Keldysh 模型进行参数化，以获得有效的相互作用。
Twisted bilayer graphene (tBLG) has recently emerged as a new platform for studying electron correlations, the strength of which can be controlled via the twist angle. Here, we study the effect of internal screening on electron-electron interactions in undoped tBLG. Using the random-phase approximation, we find that the dielectric response of tBLG drastically increases near the magic angle and is highly twist-angle dependent. As a consequence of the abrupt change of the Fermi velocity as a function of wave vectors, the screened interaction in real space exhibits attractive regions for certain twist angles near the magic angle. Attractive interactions can induce charge-density waves and superconductivity and therefore our findings could be relevant to understand the microscopic origins of the recently observed strong correlation phenomena in undoped tBLG. The resulting screened Hubbard parameters are strongly reduced and exhibit a nonlinear dependence on the twist angle. We also carry out calculations with the constrained random-phase approximation and parametrize a twist-angle dependent Keldysh model for the resulting effective interaction.