Tunable interacting composite fermion phases in a half-filled bilayer-graphene Landau level
Tunable interacting composite fermion phases in a half-filled bilayer-graphene Landau level
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DOI：
10.1038/nature23893
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发表时间：
2016-11
期刊：
影响因子：
64.8
通讯作者：
A. Zibrov;C. Kometter;Haoxin Zhou;E. Spanton;T. Taniguchi;Kenji Watanabe;M. Zaletel;A. Young
中科院分区：
文献类型：
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作者：
A. Zibrov;C. Kometter;Haoxin Zhou;E. Spanton;T. Taniguchi;Kenji Watanabe;M. Zaletel;A. Young
非阿贝尔任意子是一类准粒子，具有在不退相干的拓扑量子比特中编码量子信息的潜力。预计包含非阿贝尔任意子的实验系统包括p波超流体，具有强自旋-轨道耦合的超导系统，以及在分数量子霍尔（FQH）体系中以偶数分子出现的相互作用复合费米子的成对状态。尽管偶分母FQH状态已经在几个二维系统中被观察到，但小的能量间隙和有限的可调性阻碍了对其非阿贝尔性质的明确实验探测。本文报道了在双门控、六方氮化硼封装双层石墨烯的范德华异质结构中，在半整数朗道能级填充下观察到的稳健的偶数分母FQH相。测量到的能隙比之前观察到的大三倍。在控制载流子密度、层极化和磁场的同时，我们将这些FQH相与数值和理论模型进行了比较，并找到了配对的Pfaffian相被预测为承载非阿贝尔任意子的证据。电场控制的不同朗道能级之间的能级交叉揭示了FQH相变的级联，包括偶数分子FQH态和可压缩复合费米子液体之间的连续相变。我们的研究结果建立了石墨烯作为研究拓扑和量子临界之间相互作用以及检测非阿贝尔量子比特的原始和可调实验平台。
Non-Abelian anyons are a type of quasiparticle with the potential to encode quantum information in topological qubits protected from decoherence. Experimental systems that are predicted to harbour non-Abelian anyons include p-wave superfluids, superconducting systems with strong spin–orbit coupling, and paired states of interacting composite fermions that emerge at even denominators in the fractional quantum Hall (FQH) regime. Although even-denominator FQH states have been observed in several two-dimensional systems,,, small energy gaps and limited tunability have stymied definitive experimental probes of their non-Abelian nature. Here we report the observation of robust even-denominator FQH phases at half-integer Landau-level filling in van der Waals heterostructures consisting of dual-gated, hexagonal-boron-nitride-encapsulated bilayer graphene. The measured energy gap is three times larger than observed previously,. We compare these FQH phases with numerical and theoretical models while simultaneously controlling the carrier density, layer polarization and magnetic field, and find evidence for the paired Pfaffian phase that is predicted to host non-Abelian anyons. Electric-field-controlled level crossings between states with different Landau-level indices reveal a cascade of FQH phase transitions, including a continuous phase transition between the even-denominator FQH state and a compressible composite fermion liquid. Our results establish graphene as a pristine and tunable experimental platform for studying the interplay between topology and quantum criticality, and for detecting non-Abelian qubits.