Electron fluids in semiconductor quantum structures support low-energy excitation modes that manifest the remarkable quantum phases that emerge from fundamental interactions in two-dimensions. The benchmark semiconductor system is that of the ultra-high mobility 2D electron gas in GaAs-AlGaAs heterostructures.  Atomic layers of graphene with density tunable by electric field doping are of enormous current interest.

Inelastic light scattering (or electronic Raman scattering) at very low temperatures (reaching below 50 milliKelvin degrees) are experimental venues to study excitations of electron fluids hosted by semiconductor heterostructures.

This talk presents a brief introduction to applications of inelastic light scattering methods to studies of 2D electron systems. Recent results in quantum Hall regimes are the examples that demonstrate the power of light scattering experiments to study the low-lying excitations. These are the excitations that express distinct quantum phases of the electron liquids.  

Recent inelastic light scattering studies explore excitations of the quantum Hall fluids that reside in the second Landau level at filling factors such as nu=5/2 and nu=7/3. The quantum Hall fluids in higher Landau levels are of great current interest for applications in topologically protected quantum computations. The recent light scattering results will be evaluated to show how these experiments directly reveal spin properties and seek to elucidate the interplay among competing quantum phases of electrons that occur in higher Landau levels.¹  

(*) Work supported by the U.S National Science Foundation, by the U.S. Department of Energy, and by the U.S. Office of Naval Research.

¹ T.D. Rhone, X. Yang, J. Yan, Y. Gallais, A. Pinczuk, L.N. Pfeiffer, K.W. West, work in progress.

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