[论文解读] Fractional Quantum Anomalous Hall Effect in a Graphene Moire Superlattice

Zhengguang Lu, Tonghang Han+8 more|arXiv (Cornell University)|Sep 29, 2023

Quantum and electron transport phenomena被引用 17

一句话总结

作者报告在 rhombohedral pentalayer graphene/hBN moire 超晶格中，在零磁场下观察到整数与分数量子异常霍尔效应，具有特定的霍尔电阻阶跃和通过门位移场与充填因子调控的相位 tunability。

ABSTRACT

The fractional quantum anomalous Hall effect (FQAHE), the analog of the fractional quantum Hall effect1 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 which form the basis of topological quantum computation. So far, FQAHE has been observed only in twisted MoTe2 (t-MoTe2) at moire filling factor v > 1/2. Graphene-based moire 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 moire superlattice. At zero magnetic field, we observed plateaus of quantized Hall resistance Rxy = h/(ve^2) at filling factors v = 1, 2/3, 3/5, 4/7, 4/9, 3/7 and 2/5 of the moire superlattice respectively. These features are accompanied by clear dips in the longitudinal resistance Rxx. In addition, at zero magnetic field, Rxy equals 2h/e^2 at v = 1/2 and varies linearly with the filling factor-similar to the composite Fermi liquid (CFL) 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 CFL and FQAH states to other correlated electron states. Our graphene 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.

研究动机与目标

• Motivate the search for FQAHE at zero magnetic field in graphene-based moiré systems to enable high-quality, tunable platforms for topological states and anyonic braiding.
• Demonstrate quantized Hall plateaus at zero field corresponding to fractional fillings of the moiré superlattice and explore related phase transitions.
• Identify how gate displacement field and moiré filling control transitions between CFL-like and FQAH states and other correlated states.

提出的方法

• Study rhombohedral pentalayer graphene encapsulated with hBN forming a moiré superlattice.
• Measure Hall resistance Rxy and longitudinal resistance Rxx at zero magnetic field across varying moiré filling factors v and gate displacement field D.
• Identify quantized Rxy plateaus at h/(v e^2) for v = 1, 2/3, 3/5, 4/7, 4/9, 3/7, 2/5 with dips in Rxx.
• Observe Rxy = 2h/e^2 at v = 1/2 and its linear dependence on filling factor, analogous to a composite Fermi liquid.
• Explore phase transitions by tuning D and v between CFL/FQAH states and other correlated states.

实验结果

研究问题

• RQ1 Can graphene moiré superlattices host fractional quantum anomalous Hall states at zero magnetic field?
• RQ2 What fractional filling factors exhibit quantized Hall response in rhombohedral pentalayer graphene/moiré systems?
• RQ3 How do gate displacement field and moiré filling factor influence transitions between CFL-like, FQAH, and other correlated states?

主要发现

• Observation of quantized Hall plateaus at zero field with Rxy = h/(v e^2) for v = 1, 2/3, 3/5, 4/7, 4/9, 3/7, 2/5 and concurrent dips in Rxx.
• Rxy = 2h/e^2 at v = 1/2 at zero field, with a linear dependence on filling factor similar to CFL behavior.
• Gate displacement field D and filling factor v drive phase transitions between CFL/FQAH states and other correlated states.
• Graphene moiré platform provides a high-quality system for exploring charge fractionalization and potential non-Abelian anyonic braiding at zero field.