Gapped Excitations of unconventional FQHE states in the Second Landau Level

TL;DR

This study observes and analyzes low-energy collective excitations in unconventional fractional quantum Hall states in the second Landau level, revealing insights into their neutral excitation spectra and potential nematic phases.

Contribution

It provides the first detailed experimental characterization of collective charge and spin excitations in these fragile FQHE states, highlighting their similarities to lower Landau level states.

Findings

Identification of charge and spin excitation modes at specific energies

Universal scaling of excitation energies with lower Landau level states

Evidence of polarization dependence indicating possible nematic phases

Abstract

We report the observation of low-lying collective charge and spin excitations in the second Landau level at {\nu} = 2 + 1/3 and also for the very fragile states at {\nu} = 2 + 2/5, 2 + 3/8 in inelastic light scattering experiments. These modes exhibit a clear dependence on filling factor and temperature substantiating the unique access to the characteristic neutral excitation spectra of the incompressible FQHE states. A detailed mode analysis reveals low energy modes at around 70 {\mu}eV and a sharp mode slightly below the Zeeman energy interpreted as gap and spin wave excitation, respectively. The lowest energy collective charge excitation spectrum at {\nu} = 2 + 1/3 exhibits significant similarities and a universal scaling of the energies with its cousin state in the lowest Landau level at {\nu} = 1/3 suggesting similar underlying physics. The observed excitation spectra facilitate to distinguish between theoretical descriptions of the nature of those FQHE states. A striking polarization dependence in light scattering is discussed in the framework of anisotropic electron phases that allow for the stabilization of nematic FQHE states.