Experimental evidence of low-lying gapped excitations in the quantum fluid at nu=5/2

TL;DR

This study uses inelastic light scattering to explore the excitation spectrum of the quantum Hall fluid at filling factor 5/2, revealing gapped modes that are sensitive to filling factor variations and indicating a transition from incompressible to compressible states.

Contribution

It provides experimental evidence of low-lying gapped excitations at nu=5/2 and characterizes their behavior near the transition to a compressible state.

Findings

Gapped modes are observed only near nu=5/2.

Gapped modes disappear with small deviations in filling factor.

Spin polarization is confirmed at nu=5/2 and 2+1/3.

Abstract

The low-lying neutral excitation spectrum of the incompressible quantum Hall fluid at $\nu=5/2$ is investigated by inelastic light scattering. Gapped modes are observable only in a very narrow filling factor range centered at 5/2 at energies that overlap estimates from transport activation gaps. The modes are interpreted as critical points in the wave-vector dispersion of excitations that preserve spin orientation. For very small changes $|\delta\nu|\lesssim 0.01$ the gapped modes disappear and a continuum of low-lying excitations takes over indicating the transition from an incompressible fluid at 5/2 to a compressible state. Observations of spin wave modes indicate spin polarization of the 5/2 and 2+1/3 quantum Hall fluids.