Possible correlated insulating states in magic-angle twisted bilayer graphene under strongly competing interactions
Possible correlated insulating states in magic-angle twisted bilayer graphene under strongly competing interactions
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DOI：
10.1103/physrevb.98.081102
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发表时间：
2018-05
影响因子：
3.7
通讯作者：
M. Ochi;M. Koshino;K. Kuroki
中科院分区：
文献类型：
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作者：
M. Ochi;M. Koshino;K. Kuroki
我们通过应用于扩展Hubbard模型的精确对角化方法研究了魔角扭曲双层石墨烯（TBG）中的相关绝缘态，其中最近在现实有效模型中评估了相互作用参数。我们的模型可以处理Wannier轨道之间的竞争相互作用，因为它们有显著的重叠，这是魔角TBG的一个重要但被忽视的方面。我们提出了两个候选人的相关绝缘状态：自旋和谷铁磁带绝缘体和狄拉克半金属态的两种口味与特殊的重整化，其中口味表示一个结合的自由度与自旋和谷。后一种候选方案的重要后果之一是，它允许在整个能带结构的半填充附近出现货车霍韦奇异性（即，在狄拉克点附近）在超导性中发挥一定作用。狄拉克半金属态的两个味自由度和实验中观察到的朗道能级的双重简并度之间的一致性也是值得注意的。
We investigate correlated insulating states in magic-angle twisted bilayer graphene (TBG) by the exact diagonalization method applied to the extended Hubbard model with interaction parameters recently evaluated in the realistic effective model. Our model can handle the competing interactions among Wannier orbitals owing to their significant overlap, which is a crucial but overlooked aspect of the magic-angle TBG. We propose two candidates for the correlated insulating states: spin- and valley-ferromagnetic band insulator and the Dirac semimetallic state for two flavors with peculiar renormalization, where a flavor denotes a combined degree of freedom with spin and valley. One of the important consequences for the latter candidate is that it allows van Hove singularity near half-filling of the whole band structure (i.e., near the Dirac points) to play some role in superconductivity. The consistency between the two flavor degrees of freedom for the Dirac semimetallic state and the twofold degeneracy of the Landau level observed in the experiment is also noteworthy.