近日，美国麻省理工学院的Long Ju及其研究团队取得一项新进展。经过不懈努力，他们揭示多层石墨烯中的分数量子反常霍尔效应。相关研究成果已于2024年2月21日在国际权威学术期刊《自然》上发表。

该研究团队报道了在菱形五层石墨烯- hBN莫尔超晶格中观察到的整数和分数QAH效应。在零磁场下，研究人员分别观察到莫尔超晶格在v=1、2/3、3/5、4/7、4/9、3/7和2/5处的量子化霍尔电阻R_xy=h/ve²趋于稳定，同时纵向电阻R_xx明显下降。R_xy在v=1/2时等于2h/e²，且随v线性变化，类似于复合费米液体在高磁场下半填充的最低朗道能级。通过调节门位移场D和v，研究人员观察到从复合费米液体和FQAH态到其他关联电子态的相变。这一系统为探索零磁场下的电荷分数化和(非阿贝尔)任意子编织提供了一个理想的平台，特别是考虑到FQAHE和超导区域之间的横向结时。

据悉，分数量子反常霍尔效应(FQAHE)是零磁场下分数量子霍尔效应的类似物，预计在自发时间反演对称性破缺的拓扑平带中存在。FQAHE的证明可能会产生形成拓扑量子计算基础的非阿贝尔任意子。到目前为止，FQAHE只在扭曲的MoTe₂中被观察到，且MoTe₂填充因子为1/2。石墨烯基莫尔超晶格被认为具有优越的材料质量和更高电子迁移率的潜在优势。

附：英文原文

Title: Fractional quantum anomalous Hall effect in multilayer graphene

Author: Lu, Zhengguang, Han, Tonghang, Yao, Yuxuan, Reddy, Aidan P., Yang, Jixiang, Seo, Junseok, Watanabe, Kenji, Taniguchi, Takashi, Fu, Liang, Ju, Long

Issue&Volume: 2024-02-21

Abstract: The fractional quantum anomalous Hall effect (FQAHE), the analogue of the fractional quantum Hall effect at zero magnetic field, is predicted to exist in topological flat bands under spontaneous time-reversal-symmetry breaking. The demonstration of FQAHE could lead to non-Abelian anyons that form the basis of topological quantum computation. So far, FQAHE has been observed only in twisted MoTe₂ at a moiré filling factor v>1/2. Graphene-based moiré superlattices are believed to host FQAHE with the potential advantage of superior material quality and higher electron mobility. Here we report the observation of integer and fractional QAH effects in a rhombohedral pentalayer graphene–hBN moiré superlattice. At zero magnetic field, we observed plateaus of quantized Hall resistance R_xy=h/ve² at v=1, 2/3, 3/5, 4/7, 4/9, 3/7 and 2/5 of the moiré superlattice, respectively, accompanied by clear dips in the longitudinal resistance R_xx. R_xy equals 2h/e² at v=1/2 and varies linearly with v, similar to the composite Fermi liquid in the half-filled lowest Landau level at high magnetic fields. By tuning the gate-displacement field D and v, we observed phase transitions from composite Fermi liquid and FQAH states to other correlated electron states. Our system provides an ideal platform for exploring charge fractionalization and (non-Abelian) anyonic braiding at zero magnetic field, especially considering a lateral junction between FQAHE and superconducting regions in the same device.

DOI: 10.1038/s41586-023-07010-7

Source: https://www.nature.com/articles/s41586-023-07010-7