Microwave spectroscopic studies of the bilayer electron solid states at low Landau filling in a wide quantum well

TL;DR

This study uses microwave spectroscopy to investigate the transition to insulating bilayer electron solid states in a wide quantum well, revealing internal transitions and phase behavior not accessible by traditional transport methods.

Contribution

It provides new insights into the internal structure and phase transitions of bilayer electron solids using microwave spectroscopy.

Findings

Resonance characteristic of bilayer solid observed

Internal transitions within the insulator detected

Resonance intensity varies with carrier density

Abstract

At the low Landau filling factor $(\nu)$ termination of the fractional quantum Hall effect (FQHE) series, two-dimensional electron systems (2DESs) exhibit an insulating phase that is understood as a form of pinned Wigner solid. Here we use microwave spectroscopy to probe the transition to the insulator for a wide quantum well (WQW) sample that can support single-layer or bilayer states depending on its overall carrier density, $n$. We find the insulator exhibits a resonance, which is characteristic of a bilayer solid. The resonance also reveals a pair of transitions within the solid, which are not accessible to dc transport measurements. As $n$ is biased deeper into the bilayer solid regime, the resonance grows in specific intensity, and the transitions within the insulator disappear. These behaviors are suggestive of a picture of the insulating phase as an emulsion of liquid and solid components.