1204.4759 (U. Wurstbauer et al.)

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

U. Wurstbauer, K. W. West, L. N. Pfeiffer, A. Pinczuk

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.

View original: http://arxiv.org/abs/1204.4759