The fractional quantum Hall state (FQHS) observed at a half-filled Landau level in an interacting two-dimensional electron system (2DES) is among the most exotic states of matter as its quasiparticles are expected to be Majoranas with non-Abelian statistics. We demonstrate here the unexpected presence of such a state in a novel 2DES with a strong band-mass anisotropy. The FQHS we observe has unusual characteristics. While its Hall resistance is well-quantized at low temperatures, it exhibits highly-anisotropic in-plane transport resembling compressible stripe/nematic charge-density-wave phases. More striking, the anisotropy sets in suddenly below a critical temperature, suggesting a finite-temperature phase transition. Our observations highlight how anisotropy modifies the many-body phases of a 2DES, and should further fuel the discussion surrounding the enigmatic even-denominator FQHS.
@article{arxiv.1811.07094,
title = {Unconventional anisotropic even-denominator fractional quantum Hall state in a system with mass anisotropy},
author = {Md. Shafayat Hossain and Meng K. Ma and Y. J. Chung and L. N. Pfeiffer and K. W. West and K. W. Baldwin and M. Shayegan},
journal= {arXiv preprint arXiv:1811.07094},
year = {2018}
}