arXivDaily arXiv每日学术速递 周一至周五更新
arXiv周末暂无论文更新,休息一下吧,周末愉快~~
arXiv 2104.01178cond-mat.str-elcond-mat.mes-hall
收藏

莫尔超晶格半整数填充时的拓扑电荷密度波

Topological charge density waves at half-integer filling of a moiré superlattice

Hryhoriy Polshyn, Yuxuan Zhang, Manish A. Kumar, Tomohiro Soejima, Patrick Ledwith, Kenji Watanabe, Takashi Taniguchi, Ashvin Vishwanath, Michael P. Zaletel, Andrea F. Young

摘要:

在部分填充的平带,强的电子相互作用可能有利于间隙状态窝藏紧急拓扑与量子化霍尔电导率。在部分填充的朗道能级和霍夫施塔特能带中已经发现了涌现的拓扑态;在这两种情况下,都需要一个大的磁场来设计下面的平带。最近在窄带莫尔系统中观察到量子反常霍尔效应(QAH),理论预言这种相位甚至可以在零磁场下实现。在这里,我们报告的实验观察的绝缘体陈数$C=1$在零磁场极限在$ν=3/2$和$7/2$填充的莫尔超晶格单胞在扭曲的单层-双层石墨烯(tMBG)。我们在$ν$的半整数值处对陈氏绝缘体的观察表明,除了自旋和谷铁磁性之外,超晶格晶胞还具有自发加倍。Hartree-Fock计算证实了这一点,该计算在底层$C=2$能带的半填充处发现了拓扑电荷密度波基态,其中Berry曲率在占据态和未占据态之间均匀分配。我们发现平移对称破缺序参量均匀分布在整个折叠超晶格布里渊区,表明系统处于平带、强关联极限。我们的研究结果表明,量子几何和库仑相互作用的相互作用在莫尔带允许拓扑相位在分数超晶格填充自发地打破时间反演对称性,在追求零磁场相位窝藏分数统计作为元激发或绑定到晶格位错的先决条件。

英文摘要:

At partial filling of a flat band, strong electronic interactions may favor gapped states harboring emergent topology with quantized Hall conductivity. Emergent topological states have been found in partially filled Landau levels and Hofstadter bands; in both cases, a large magnetic field is required to engineer the underlying flat band. The recent observation of quantum anomalous Hall effects (QAH) in narrow band moiré systems has led to the theoretical prediction that such phases may be realized even at zero magnetic field. Here we report the experimental observation of insulators with Chern number $C=1$ in the zero magnetic field limit at $ν=3/2$ and $7/2$ filling of the moiré superlattice unit cell in twisted monolayer-bilayer graphene (tMBG). Our observation of Chern insulators at half-integer values of $ν$ suggests spontaneous doubling of the superlattice unit cell, in addition to spin- and valley-ferromagnetism. This is confirmed by Hartree-Fock calculations, which find a topological charge density wave ground state at half filling of the underlying $C=2$ band, in which the Berry curvature is evenly partitioned between occupied and unoccupied states. We find the translation symmetry breaking order parameter is evenly distributed across the entire folded superlattice Brillouin zone, suggesting that the system is in the flat band, strongly correlated limit. Our findings show that the interplay of quantum geometry and Coulomb interactions in moiré bands allows for topological phases at fractional superlattice filling that spontaneously break time-reversal symmetry, a prerequisite in pursuit of zero magnetic field phases harboring fractional statistics as elementary excitations or bound to lattice dislocations.

机构、总结、中文摘要均由AI分析而来,可能存在错误,请以论文正文为准。

↑