## 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.

Original language | English (US) |
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Article number | 165438 |

Journal | Physical Review B |

Volume | 95 |

Issue number | 16 |

DOIs | |

State | Published - Apr 21 2017 |

## All Science Journal Classification (ASJC) codes

- Electronic, Optical and Magnetic Materials
- Condensed Matter Physics