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Interlayer fractional quantum Hall effect in a coupled graphene double layer

Abstract

When a strong magnetic field is applied to a two-dimensional electron system, interactions between the electrons can cause fractional quantum Hall (FQH) effects1,2. Bringing two two-dimensional conductors close to each other, a new set of correlated states can emerge due to interactions between electrons in the same and opposite layers3,4,5,6. Here we report interlayer-correlated FQH states in a device consisting of two parallel graphene layers separated by a thin insulator. Current flow in one layer generates different quantized Hall signals in the two layers. This result is interpreted using composite fermion (CF) theory7 with different intralayer and interlayer Chern–Simons gauge-field couplings. We observe FQH states corresponding to integer values of CF Landau level (LL) filling in both layers, as well as ‘semiquantized’ states, where a full CF LL couples to a continuously varying partially filled CF LL. We also find a quantized state between two coupled half-filled CF LLs and attribute it to an interlayer CF exciton condensate.

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Fig. 1: Interlayer-correlated states at fractional filling factors in graphene double layer with equal densities.
Fig. 2: Interlayer correlation through quasiparticle pairing.
Fig. 3: Semiquantized fractional Hall states.

Data availability

The data that support the plots within this paper and other findings of this study are available from the corresponding author on reasonable request.

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Acknowledgements

The major experimental work is supported by DOE (DE-SC0012260). The theoretical analysis was supported by the Science and Technology Center for Integrated Quantum Materials, NSF grant no. DMR-1231319. P.K. acknowledges partial support from the Gordon and Betty Moore Foundation’s EPiQS Initiative through grant GBMF4543. K.W. and T.T. acknowledge support from the Elemental Strategy Initiative conducted by MEXT, Japan, and CREST(JPMJCR15F3), JST. A portion of this work was performed at the National High Magnetic Field Laboratory, which is supported by the National Science Foundation Cooperative Agreement no. DMR-1157490* and the State of Florida. Nanofabrication was performed at the Center for Nanoscale Systems at Harvard, supported in part by NSF NNIN award ECS-00335765. In preparation of this manuscript, we are aware of related work done by J. I. A. Li et al. We thank B. Rosenow, J. I. A. Li and C. Dean for helpful discussions.

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X.L. and P.K. conceived the experiment. X.L. and Z.H. fabricated the samples and performed the measurements. X.L. analysed the data. B.H. conducted the theoretical analysis. X.L., B.I.H. and P.K. wrote the paper. K.W. and T.T. supplied hBN crystals.

Corresponding author

Correspondence to Philip Kim.

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The authors declare no competing interests.

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Peer review information: Nature Physics thanks Timo Hyart, Emanuel Tutuc and the other, anonymous, reviewer(s) for their contribution to the peer review of this work.

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Supplementary information

Supplementary Information

Additional theoretical details, Supplementary Figs. 1–4 and Supplementary references 1–12.

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Liu, X., Hao, Z., Watanabe, K. et al. Interlayer fractional quantum Hall effect in a coupled graphene double layer. Nat. Phys. 15, 893–897 (2019). https://doi.org/10.1038/s41567-019-0546-0

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