Evidence for a ν=5/2 fractional quantum Hall nematic state in parallel magnetic fields

We report magnetotransport measurements for the fractional quantum Hall state at filling factor ν= 5/2 as a function of applied parallel magnetic field (B_||). As B_|| is increased, the 5/2 state becomes increasingly anisotropic, with the in-plane resistance along the direction of B_|| becoming more than 30 times larger than in the perpendicular direction. Despite the very large resistance anisotropy, the anisotropy ratio remains constant over a relatively large temperature range, yielding an energy gap which is the same for both directions. Our data are qualitatively consistent with a fractional quantum Hall nematic phase.