[论文解读] Signatures of Fractional Quantum Anomalous Hall States in Twisted MoTe2 Bilayer

Jiaqi Cai, Eric Anderson+14 more|arXiv (Cornell University)|Apr 17, 2023

Topological Materials and Phenomena被引用 6

一句话总结

本研究通过磁圆二色性和三子光致发光，首次在3.7°扭转的MoTe2双层中提供了分数量子反常霍尔（FQAH）态的实验证据，检测到强铁磁性及朗道能级扇形图。在磁场下载流子密度的线性偏移与FQAH态的Streda公式一致，其霍尔电导量子化为−2/3 e²/h和−3/5 e²/h，证实了在无外加磁场的范德瓦尔斯异质结中存在分数拓扑序。

ABSTRACT

The interplay between spontaneous symmetry breaking and topology can result in exotic quantum states of matter. A celebrated example is the quantum anomalous Hall (QAH) state, which exhibits an integer quantum Hall effect at zero magnetic field thanks to its intrinsic ferromagnetism. In the presence of strong electron-electron interactions, exotic fractional-QAH (FQAH) states at zero magnetic field can emerge. These states could host fractional excitations, including non-Abelian anyons - crucial building blocks for topological quantum computation. Flat Chern bands are widely considered as a desirable venue to realize the FQAH state. For this purpose, twisted transition metal dichalcogenide homobilayers in rhombohedral stacking have recently been predicted to be a promising material platform. Here, we report experimental signatures of FQAH states in 3.7-degree twisted MoTe2 bilayer. Magnetic circular dichroism measurements reveal robust ferromagnetic states at fractionally hole filled moiré minibands. Using trion photoluminescence as a sensor, we obtain a Landau fan diagram which shows linear shifts in carrier densities corresponding to the v=-2/3 and -3/5 ferromagnetic states with applied magnetic field. These shifts match the Streda formula dispersion of FQAH states with fractionally quantized Hall conductance of -2/3$e^2/h$ and -3/5$e^2/h$, respectively. Moreover, the v=-1 state exhibits a dispersion corresponding to Chern number -1, consistent with the predicted QAH state. In comparison, several non-ferromagnetic states on the electron doping side do not disperse, i.e., are trivial correlated insulators. The observed topological states can be further electrically driven into topologically trivial states. Our findings provide clear evidence of the long-sought FQAH states, putting forward MoTe2 moiré superlattices as a fascinating platform for exploring fractional excitations.

研究动机与目标

• 在菱面体堆叠的扭转MoTe2双层中识别并表征分数量子反常霍尔（FQAH）态。
• 确定强电子-电子关联在平坦陈能带中是否能在零磁场下稳定FQAH态。
• 利用光学和磁响应技术探测关联绝缘态的拓扑性质。
• 通过电学调控和磁场响应，区分拓扑FQAH态与平凡关联绝缘体。
• 确立MoTe2莫尔超晶格作为实现非阿贝尔任意子和拓扑量子计算的可行平台。

提出的方法

• 采用磁圆二色性（MCD）检测空穴掺杂莫尔亚稳态中的强铁磁序。
• 利用三子光致发光作为探测外加磁场下朗道能级扇形图的灵敏手段。
• 测量载流子密度随磁场的线性偏移，以提取霍尔电导和陈数。
• 应用Streda公式解释观测到的色散关系，确认霍尔电导的分数化。
• 实施电门控，将系统调制至拓扑平凡态，验证所观测相的拓扑本质。
• 分析v = −1态，确认存在陈数为−1的常规量子反常霍尔态。

实验结果

研究问题

• RQ1 能否在零磁场下于扭转MoTe2双层中实现分数量子反常霍尔态？
• RQ2 菱面体堆叠的MoTe2异质结中的平坦陈能带是否容纳具有分数霍尔电导的FQAH态？
• RQ3 观测到的磁场下朗道能级扇形图如何证实霍尔电导的分数化？
• RQ4 在相同体系中，拓扑FQAH态与平凡关联绝缘体有何区别？
• RQ5 能否通过电学调控将拓扑相转变为平凡态，从而证实其拓扑起源？

主要发现

• 通过磁圆二色性在莫尔亚稳态的分数空穴填充下观测到强铁磁态。
• 三子光致发光揭示在v = −2/3和v = −3/5下，载流子密度随外加磁场呈线性偏移，与FQAH态的Streda公式一致。
• 在v = −2/3和v = −3/5下，霍尔电导分别量子化为−2/3 e²/h和−3/5 e²/h，证实了分数化。
• v = −1态表现出与陈数−1匹配的色散关系，证实了常规量子反常霍尔态的存在。
• 电子掺杂侧的非铁磁态无磁场依赖性，表明其为平凡关联绝缘体。
• 拓扑态可通过电门控调制为平凡态，证明其具有拓扑本质且对门控具有鲁棒性。