Resonant inelastic light scattering investigation of low-lying gapped excitations in the quantum fluid at ν=5/2

Phys Rev Lett. 2013 Jan 11;110(2):026801. doi: 10.1103/PhysRevLett.110.026801. Epub 2013 Jan 7.


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.