The low-lying neutral excitation spectrum of the incompressible quantum Hall fluid at ν=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 ∣δν∣≲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.
@article{arxiv.1204.4759,
title = {Experimental evidence of low-lying gapped excitations in the quantum fluid at nu=5/2},
author = {U. Wurstbauer and K. W. West and L. N. Pfeiffer and A. Pinczuk},
journal= {arXiv preprint arXiv:1204.4759},
year = {2012}
}