Tilt-induced anisotropic to isotropic phase transition at ν = 5/2.

A modest in-plane magnetic field B(∥) is sufficient to destroy the fractional quantized Hall states at ν = 5/2 and 7/2 and replace them with anisotropic compressible phases. Remarkably, we find that at larger B(∥) these anisotropic phases can themselves be replaced by isotropic compressible phases reminiscent of the composite fermion fluid at ν = 1/2. We present strong evidence that this transition is a consequence of the mixing of Landau levels from different electric subbands. We also report surprising dependences of the energy gaps at ν = 5/2 and 7/3 on the width of the confinement potential.