Enhancement of the $\nu = 5/2$ Fractional Quantum Hall State in a Small In-Plane Magnetic Field

TL;DR

This study demonstrates that the fractional quantum Hall state at filling factor 5/2 is enhanced by a small in-plane magnetic field in a high-quality GaAs/AlGaAs quantum well, revealing new insights into its spin texture and phase transitions.

Contribution

It provides the first evidence that a small in-plane magnetic field can strengthen the 5/2 fractional quantum Hall state in ultra-clean quantum wells, suggesting a role for Skyrmion spin textures.

Findings

The 5/2 resistance minimum and Hall plateau strengthen with tilt angle up to 25°.

Activation gaps of 7/3 and 8/3 states increase with tilt angle.

At tilt angles above 60°, the 5/2 state becomes a compressible Fermi liquid.

Abstract

Using a 50-nm width, ultra-clean GaAs/AlGaAs quantum well, we have studied the Landau level filling factor $\nu = 5/2$ 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+$p/(2p\pm1)$], $p =$ 1, 2 can be identified. Based on our results, we discuss the relevance of a Skyrmion spin texture at $\nu = 5/2$ 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).