Using a 50-nm width, ultra-clean GaAs/AlGaAs quantum well, we have studied the Landau level filling factor $ u = 5/2$ fractional quantum Hall effect in a perpendicular magnetic field $B sim$ 1.7 T and determined its dependence on tilted magnetic fields. Contrary to all previous results, the 5/2 resistance minimum and the Hall plateau are found to strengthen continuously under an increasing tilt angle $0 < theta < 25^circ$ (corresponding to an in-plane magnetic field 0 $<$ $B_parallel$ $< 0.8$ T). In the same range of $theta$ the activation gaps of both the 7/3 and the 8/3 states are found to increase with tilt. The 5/2 state transforms into a compressible Fermi liquid upon tilt angle $theta > 60^circ$, and the composite fermion series [2+$p/(2ppm1)$], $p =$ 1, 2 can be identified. Based on our results, we discuss the relevance of a Skyrmion spin texture at $ u = 5/2$ associated with small Zeeman energy in wide quantum wells, as proposed by W$acute{text o}$js $et$ $al$., Phys. Rev. Lett. 104, 086801 (2010).
Download