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# Search for composite fermions at filling factor 5/2: Role of Landau level and subband index

## Author(s): Mueed, MA; Kamburov, D; Hossain, Md Shafayat; Pfeiffer, LN; West, KW; et al

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 Abstract: The pairing of composite fermions (CFs), i.e., electron-flux quasiparticles, is commonly proposed to explain the even-denominator fractional quantum Hall state observed at ν=5/2 in the first excited (N=1) Landau level (LL) of a two-dimensional electron system (2DES). While well established to exist in the lowest (N=0) LL, much is unknown about CFs in the N=1 LL. Here we carry out geometric resonance measurements to detect CFs at ν=5/2 by subjecting the 2DES to a one-dimensional density modulation. Our data, taken at a temperature of 0.3 K, reveal no geometric resonances for CFs in the N=1 LL. In stark contrast, we observe clear signatures of such resonances when ν=5/2 is placed in the N=0 LL of the antisymmetric subband by varying the 2DES width. This finding implies that the CFs' mean free path is significantly smaller in the N=1 LL compared to the N=0 LL. Our additional data as a function of in-plane magnetic field highlight the role of subband index and establish that CFs at ν=5/2 in the N=0 LL are more anisotropic in the symmetric subband than in the antisymmetric subband. Publication Date: Apr-2017 Electronic Publication Date: 21-Apr-2017 Citation: Mueed, MA, Kamburov, D, Hossain, Md Shafayat, Pfeiffer, LN, West, KW, Baldwin, KW, Shayegan, M. (2017). Search for composite fermions at filling factor 5/2: Role of Landau level and subband index. Physical Review B, 95 (16), 10.1103/PhysRevB.95.165438 DOI: doi:10.1103/PhysRevB.95.165438 ISSN: 2469-9950 EISSN: 2469-9969 Type of Material: Journal Article Journal/Proceeding Title: Physical Review B Version: Author's manuscript

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