Observation of a fractional quantum hall state at ν=1/4 in a wide GaAs quantum well

We report the observation of an even-denominator fractional quantum Hall state at ν=1/4 in a high quality, wide GaAs quantum well. The sample has a quantum well width of 50 nm and an electron density of ne=2.55×1011cm-2. We have performed transport measurements at T∼35mK in magnetic fields up to 45 T. When the sample is perpendicular to the applied magnetic field, the diagonal resistance displays a kink at ν=1/4. Upon tilting the sample to an angle of θ=20.3° a clear fractional quantum Hall state emerges at ν=1/4 with a plateau in the Hall resistance and a strong minimum in the diagonal resistance.