Magnetorotons at n =5/2 Aron Pinczuk, Columbia University, DMR 0803691

1. Magnetorotons at n=5/2Aron Pinczuk, Columbia University, DMR 0803691 The enigmatic fractional quantum Hall effect at filling factor n=5/2 is of great interest because its physics is linked to key fundamental interactions and its quasi-particle excitations may obey non-Abelian braiding statistics. We observed low-lying gapped excitations of the fractional quantum Hall fluid at n=5/2 by resonant inelastic light scattering (RILS) methods at low temperatures (less than 40mK). The lowest and strongest mode shown in the figure (at DR)is interpreted as a magnetoroton of dispersive collective excitations of the quantum fluid. For the first time in the 5/2 state the observed energies show overall agreement with calculations that incorporate realistic effects such as finite width of the 2D layer and Landau level mixing. RILS experiments could offer tests of current theories that describe physics and evaluate low-lying collective excitation spectra of quasi-particles at n=5/2, and that explore non-Abelian character of the excitations. • Color plot of resonant inelastic light scattering • intensity at n=5/2 as function of incident photon • energy. Significant spectra are shown in the inset. • (b) Empirical wave vector dispersion showing a • magnetoroton minimum in the collective excitation • spectrum of the electron quantum fluid at n=5/2. • The inset shows the scattering geometry.

2. Trevor D. Rhone Magnetorotons at n=5/2Aron Pinczuk, Columbia University, DMR 0803691 Impact: Studies of intriguing quantum phases of electrons in low-dimensional structures reveal new properties with major impact on key research areas of contemporary science Education One Columbia pos-doc (Ursula Wurstbauer), and one Columbia graduate student (Trevor D. Rhone) are the leaders in the research supported by this NSF award. In this period one graduate student (Albert Rigosi ) and one undergraduate student (Antonio Levy) actively participated in the research. The projects benefit from collaborations with other colleagues. Networking with major centers at Columbia enhances the impact of the research. Collaborations abroad are in Pisa, Italy (group of Vittorio Pellegrini), Chernogolovka, Russia (group of Igor Kukushkin) and Paris, France (Yann Gallais). The participants explore frontiers of quantum physics and materials science. Junior scientists are being trained in ultra-low temperature techniques, semiconductor physics, material processing and clean-room methods Albert Rigosi Ursula Wurstbauer