ν=5/2 fractional quantum hall effect at 10 T: Implications for the Pfaffian state

We report on the magnetotransport (including tilt fields) around Landau level filling factor ν=5/2 in a high-purity modulation-doped GaAs/AlGaAs quantum well with twice the electron density of standard samples. A quantized 5/2 Hall plateau is observed at B≈10T, with an activation gap ∼125mK; the plateau can persist up to ∼25° tilt field. This finding is discussed in the context of a proposed Moore-Read Pfaffian (or anti-Pfaffian) wave function being a possible ground state at 5/2. The tilt fields induce a background resistance at 5/2 that could be either isotropic or anisotropic, depending simply on the in-plane magnetic field direction with respect to the GaAs crystalline axis. Such data indicate a substantial coupling between the 5/2 collective phases and the GaAs crystal.