Interlayer fractional quantum Hall effect in a coupled graphene double layer

• Published in: Nature physics Vol. 15; no. 9; pp. 893 - 897
• Main Authors: Liu, Xiaomeng, Hao, Zeyu, Watanabe, Kenji, Taniguchi, Takashi, Halperin, Bertrand I., Kim, Philip
• Format: Journal Article
• Language: English
• Published: London Nature Publishing Group UK 01.09.2019; Nature Publishing Group; Nature Publishing Group (NPG)
• Subjects: 639/766; 639/766/1130; 639/766/119; 639/766/119/2792; 639/766/119/2794; Atomic; Classical and Continuum Physics; Complex Systems; Condensed Matter Physics; Conductors; Couplings; Electrons; Excitons; Fermions; Graphene; Interlayers; Letter; Magnetic fields; Mathematical and Computational Physics; Molecular; Optical and Plasma Physics; Physics; Physics and Astronomy; Quantum Hall effect; Theoretical; Thin films
• DOI: 10.1038/s41567-019-0546-0
• ISSN: 1745-2473

When a strong magnetic field is applied to a two-dimensional electron system, interactions between the electrons can cause fractional quantum Hall (FQH) effects 1 , 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 layers 3 – 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) theory 7 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. Transport data reveal interlayer composite fermion fractional quantum Hall states in double-layer graphene. The authors also show that these can pair up to form an interlayer composite fermion exciton condensate.