Competing quantum Hall phases in the second Landau level in low density limit

TL;DR

This study investigates quantum Hall phases in low-density GaAs quantum wells, revealing anisotropic behavior at =7/2 and strong fractional states at =8/3, 5/2, and 7/3, highlighting the role of electron interactions and Landau level mixing.

Contribution

It provides experimental evidence of competing quantum Hall phases influenced by Landau level mixing in low-density regimes.

Findings

Anisotropic transport at =7/2 in low-density samples.

Observation of strong fractional quantum Hall states at =8/3, 5/2, 7/3.

Indication that the 5/2 state may be spin unpolarized at low density.

Abstract

We present in this Letter the results from two high quality, low density GaAs quantum wells. In sample A of electron density n=5.0x10^10 cm^-2, anisotropic electronic transport behavior was observed at \nu=7/2 in the second Landau level. We believe that the anisotropy is due to the large Landau level mixing effect in this sample. In sample B of density 4.1x10^10 cm^-2, strong 8/3, 5/2, and 7/3 fractional quantum Hall states were observed. Furthermore, our energy gap data suggest that, similar to the 8/3 state, the 5/2 state may also be spin unpolarized in the low density limit. The results from both samples show that the strong electron-electron interactions and a large Landau level mixing effect play an import role in the competing ground states in the second landau level.