Microwave resonance of the reentrant insulating quantum Hall phases in the 1st excited Landau Level

TL;DR

This study measures microwave conductivity in the first excited Landau level, revealing resonances indicative of bubble phase crystal formation at very low temperatures.

Contribution

It provides the first microwave conductivity measurements of reentrant insulating quantum Hall phases in the first excited Landau level, supporting the bubble phase crystal hypothesis.

Findings

Resonance detected around filling factor ν=2.58

Weaker frequency dependence at ν=2.42 and 2.28

Results consistent with bubble phase crystal formation

Abstract

We present measurements of the real diagonal microwave conductivity of the reentrant insulating quantum Hall phases in the first excited Landau level at temperatures below 50 mK. A resonance is detected around filling factor $\nu=2.58$ and weaker frequency dependence is seen at $\nu=2.42$ and 2.28. These measurements are consistent with the formation of a bubble phase crystal centered around these $\nu$ at very low temperatures.