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

We report magnetotransport measurements for the fractional quantum Hall state at filling factor $\ensuremath{\nu}=$ 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.