Fractional Quantum Hall Effect in the Second Landau Level

TL;DR

This paper reports activation gap measurements of fractional quantum Hall states in the second Landau level, revealing large gaps for certain states and suggesting the emergence of exotic correlations different from those in the lowest Landau level.

Contribution

It provides the first detailed activation gap measurements of FQHE states in the second Landau level, highlighting the potential for novel quantum correlations.

Findings

Large activation gap (~600 mK) for the 5/2 FQHE state.

Observation of signatures for 14 and 5 FQHE states in high and low mobility samples.

Measured gaps align with theoretical predictions after corrections.

Abstract

We present activation gap measurements of the fractional quantum Hall effect (FQHE) in the second Landau level. Signatures for 14 (5) distinct incompressible FQHE states are seen in a high (low) mobility sample with the enigmatic 5/2 even denominator FQHE having a large activation gap of $\sim$600 ($\sim$300mK) in the high (low) mobility sample. Our measured large relative gaps for 5/2, 7/3, and 8/3 FQHE indicate emergence of exotic FQHE correlations in the second Ladau level, possibly quite different from the well-known lowest Landau level Laughlin correlations. Our measured 5/2 gap is found to be in reasonable agreement with the theoretical gap once finite width and disorder broadening corrections are taken into account.