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Kekulé Spiral Order at All Nonzero Integer Fillings in Twisted Bilayer Graphene
Physical Review X ( IF 12.5 ) Pub Date : 2021-12-30 , DOI: 10.1103/physrevx.11.041063
Y. H. Kwan , G. Wagner , T. Soejima , M. P. Zaletel , S. H. Simon , S. A. Parameswaran , N. Bultinck

We study magic angle graphene in the presence of both strain and particle-hole symmetry breaking due to nonlocal interlayer tunneling. We perform a self-consistent Hartree-Fock study that incorporates these effects alongside realistic interaction and substrate potentials and explore a comprehensive set of competing orders including those that break translational symmetry at arbitrary wave vectors. We find that at all nonzero integer fillings very small strains, comparable to those measured in scanning tunneling experiments, stabilize a fundamentally new type of time-reversal-symmetric and spatially nonuniform order. This order, which we dub the “incommensurate Kekulé spiral” (IKS) order, spontaneously breaks both the emergent valley-charge conservation and moiré translation symmetries but preserves a modified translation symmetry T^—which simultaneously shifts the spatial coordinates and rotates the U(1) angle which characterizes the spontaneous intervalley coherence. We discuss the phenomenological and microscopic properties of this order. We argue that our findings are consistent with all experimental observations reported so far, suggesting a unified explanation of the global phase diagram in terms of the IKS order.

中文翻译:

扭曲双层石墨烯中所有非零整数填充的 Kekulé 螺旋顺序

我们研究了由于非局部层间隧穿导致的应变和粒子-空穴对称性破坏的魔角石墨烯。我们进行了一项自洽的 Hartree-Fock 研究,将这些影响与现实相互作用和底物电位结合起来,并探索了一组全面的竞争秩序,包括那些在任意波矢量上破坏平移对称性的秩序。我们发现,在所有非零整数填充中,非常小的应变(与扫描隧道实验中测量的应变相当)稳定了一种全新的时间反转对称和空间非均匀顺序。这个顺序,我们称之为“非公度凯库勒螺旋”(IKS)顺序,自发地打破了涌现的谷电荷守恒和莫尔平移对称性,但保留了修改后的平移对称性^——同时移动空间坐标和旋转 (1)表征自发间隔相干的角度。我们讨论了这个秩序的现象学和微观特性。我们认为我们的发现与迄今为止报告的所有实验观察结果一致,表明根据 IKS 顺序对全局相图进行了统一解释。
更新日期:2021-12-31
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