Observation of a Fractional Quantum Hall State at $��=1/4$ in a Wide GaAs Quantum Well

We report the observation of an even-denominator fractional quantum Hall (FQH) state at $��=1/4$ in a high quality, wide GaAs quantum well. The sample has a quantum well width of 50 nm and an electron density of $n_e=2.55\times10^{11}$ cm$^{-2}$. We have performed transport measurements at $T\sim35$ mK in magnetic fields up to 45 T. When the sample is perpendicular to the applied magnetic field, the diagonal resistance displays a kink at $��=1/4$. Upon tilting the sample to an angle of $��=20.3^o$ a clear FQH state at emerges at $��=1/4$ with a plateau in the Hall resistance and a strong minimum in the diagonal resistance.
Accepted for publication in Phys. Rev. Lett