Experimental studies of the fractional quantum Hall effect in the first excited Landau level

TL;DR

This paper presents experimental data on fractional quantum Hall states in the first excited Landau level, highlighting the effects of disorder, energy gaps, and the unexpected disappearance of certain states in ultra-high mobility samples.

Contribution

It provides new experimental insights into the behavior of FQHE states in the first excited Landau level, especially regarding disorder effects and the absence of the nu=13/5 state.

Findings

Disorder significantly affects the energy gap at nu=5/2.

The nu=19/8 state has an energy gap of approximately 5mK.

The nu=13/5 state is missing in ultra-high quality samples, possibly due to spin polarization.

Abstract

We present a spectrum of experimental data on the fractional quantum Hall effect (FQHE) states in the first excited Landau level, obtained in an ultrahigh mobility two-dimensional electron system (2DES) and at very low temperatures and report the following results: For the even-denominator FQHE states, the sample dependence of the nu=5/2 state clearly shows that disorder plays an important role in determining the energy gap at nu=5/2. For the developing nu=19/8 FQHE state the temperature dependence of the Rxx minimum implies an energy gap of ~5mK.The energy gaps of the odd-denominator FQHE states at nu=7/3 and 8/3 also increase with decreasing disorder, similar to the gap at 5/2 state. Unexpectedly and contrary to earlier data on lower mobility samples, in this ultra-high quality specimen, the nu=13/5 state is missing, while its particle-hole conjugate state, the nu=12/5 state, is a fully developed FQHE state. We speculate that this disappearance might indicate a spin polarization of the nu=13/5 state. Finally, the temperature dependence is studied for the two-reentrant integer quantum Hall states around nu=5/2 and is found to show a very narrow temperature range for the transition from quantized to classical value.