Microwave spectroscopy of the low-filling-factor bilayer electron solid in a wide quantum well.

A T Hatke,K W West,M Shayegan,K W Baldwin,Y Liu,L N Pfeiffer,L W Engel

doi:10.1038/ncomms8071

A T Hatke, K W West + Show 5 more

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https://doi.org/10.1038/ncomms8071

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Abstract

At the low Landau filling factor termination of the fractional quantum Hall effect series, two-dimensional electron systems 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 sample that can support single-layer or bilayer states depending on its overall carrier density. We find that 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 density is biased deeper into the bilayer solid regime, the resonance grows in specific intensity, and the transitions within the insulator disappear. These behaviours are suggestive of a picture of the insulating phase as an emulsion of liquid and solid components.

Highlights

At the low Landau filling factor termination of the fractional quantum Hall effect series, two-dimensional electron systems exhibit an insulating phase that is understood as a form of pinned Wigner solid
Earlier studies of bilayer pinning modes[16,20,21] used double quantum wells, for which the layers are defined by a barrier, and 1C–2C transitions were considered in refs 20,21
In this paper we use microwave pinning-mode spectroscopy on a Wide quantum wells (WQWs) to probe the low-n bilayer insulator, which is understood as a bilayer electron solid

Summary

Introduction

At the low Landau filling factor termination of the fractional quantum Hall effect series, two-dimensional electron systems exhibit an insulating phase that is understood as a form of pinned Wigner solid. We use microwave spectroscopy to probe the transition to the insulator for a wide quantum well sample that can support single-layer or bilayer states depending on its overall carrier density. At small g the two-dimensional (2D) electron system (2DES) behaves like a single layer, exhibiting a one-component (1C) Wigner solid for n below the 1/5 fractional quantum Hall effect (FQHE), and for a narrow re-entrant range[7] above it. Microwave spectroscopy is ideal for studies of electron solids since these exhibit pinning mode resonances[8,9,10,11,12,13,14,15,16,17,18,19,20,21,22,23], in which pieces of the solid oscillate within the potential of the residual disorder. Our observations are interpreted in terms of intermediate phases, possibly involving bilayer solid and nonresonant liquid components

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