Chiral Spin Density Wave and d plus id Superconductivity in the Magic-Angle-Twisted Bilayer Graphene
Chiral Spin Density Wave and d plus id Superconductivity in the Magic-Angle-Twisted Bilayer Graphene
复制标题
魔角扭曲双层石墨烯中的手性自旋密度波和 d 加 id 超导性
DOI：
10.1103/physrevlett.121.217001
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发表时间：
2018-11-21
影响因子：
8.6
通讯作者：
Yang, Fan
中科院分区：
文献类型：
--
作者：
Liu, Cheng-Cheng;Zhang, Li-Da;Yang, Fan
我们将新合成的魔角扭曲双层石墨烯超导体建模为超结构蜂窝晶格上的两个p（x，y）（-）类Wannier轨道，其中跳跃积分通过对称性分析的Slater-Koster公式构造。这个简单的模型所表现出的特性与严格的计算和实验观察都很好地一致。在实验中发现了与相关绝缘体和非常规超导性相关的掺杂能级中存在货车霍韦奇异性和费米面嵌套，据此我们确定这两个相为弱耦合的费米面不稳定性。然后，与排斥哈伯德相互作用打开，我们进行了基于随机相位近似的计算，以确定电子不稳定性。结果发现，在半填充附近，在相关绝缘态附近存在手征d + id拓扑超导，确定为非共面手征自旋密度波有序态，具有量子反常霍尔效应。在我们的方法得到的相图是定性与实验一致。
We model the newly synthesized magic-angle-twisted bilayer graphene superconductor with two p(x,y)(-) like Wannier orbitals on the superstructure honeycomb lattice, where the hopping integrals are constructed via the Slater-Koster formulism by symmetry analysis. The characteristics exhibited in this simple model are well consistent with both the rigorous calculations and experiment observations. A van Hove singularity and Fermi-surface (FS) nesting are found in the doping levels relevant to the correlated insulator and unconventional superconductivity revealed experimentally, based on which we identify the two phases as weak-coupling FS instabilities. Then, with repulsive Hubbard interactions turned on, we performed random-phase-approximation based calculations to identify the electron instabilities. As a result, we find chiral d + id topological superconductivity bordering the correlated insulating state near half-filling, identified as noncoplanar chiral spin-density wave ordered state, featuring the quantum anomalous Hall effect. The phase diagram obtained in our approach is qualitatively consistent with experiments.