Metastable nematicity at ν = 7/2 in GaAs quantum wells mediated by nuclear spin polarization

Isotropic fractional quantum Hall states at ν=5/2 and ν=7/2 in the N=1 Landau level may undergo a transition to compressible anisotropic nematic states as Hamiltonian parameters are varied. Here, we report the observation of a metastable anisotropic state at ν=7/2 that relaxes to an isotropic state depending on the degree of nuclear spin polarization in the GaAs quantum well. The two-dimensional electron gas (2DEG) resides in a 30 nm quantum well with density n = 1.05x10¹¹ cm^-2 and mobility μ = 18x10⁶ cm²/Vs. For all temperatures down to T=10 mK, transport remains isotropic at ν=7/2 when sweeping the magnetic field from ν=4 to ν=3. However transport at ν=7/2 becomes highly anisotropic when sweeping from high magnetic field to lower values. With currently flowing along the [01-1] direction a strong resistance peak is observed while a local minima is observed for current flowing along the [011] direction. The anisotropy becomes stronger as the starting magnetic field for the sweep down is increased. The resistance peak along the [01-1] is also metastable. Once the field sweep is terminated, the resistance peak at ν=7/2 begins to decay with time. The field, temperature, and temporal dependence of this behavior indicate the impact of the nuclear spin polarization state.