1. Excitations in Landau Levels of 2D Quantum Fluids Aron Pinczuk, Columbia University, DMR 1306976 This new award will support studies of intriguing emergent quantum phases in two-dimensional electron systems. The striking quantum fluids occur in highest quality semiconductor hetero-structures in large magnetic fields. Partially populated higher Landau levels are hosts to remarkable competing phases (see figure). We study these phases by measurements of low-lying excitations in charge and/or spin degrees of freedom by means of unique resonant inelastic light scattering methods that are developed in the group of the PI [1-4]. The experiments are at the low temperatures below 50 milliKelvin degrees that are achieved in dilution refrigerators. [1] T.D. Rhone et al, Phys. Rev. Lett., 106, 096803 (2011). [2] T.D. Rhone et al, Phys. Rev. Lett., 106, 196805 (2011). [3] U. Wurstbauer et al, Phys. Rev. Lett. 107, 066804 (2011). [4] U. Wurstbauer et al. Phys. Rev. Lett., 110, 026801 (2013). laser Paired CFs Stripe Phase Bubble Phase Top panel. Illustration of different quantum phases that are expected in states of the 2D electron gas in the second Landau level. The laser used in optical experiment is shown in red. Bottom panel. Left side is a schematic rendition of optical experiments at very low temperature in a total magnetic field B T. A diagram for inelastic light scattering by an excitation of the 2D electron gas of momentum q is shown in the right side.

2. Education One part-time Columbia post-doc and one full-time Columbia graduate student will be leading these studies.. Collaborations with the Peiffer group (Princeton) and the Manfra group (Purdue) offer access to world-class semiconductor hetero-structures. The projects will benefit from the theoretical support of the Jain group (Penn State). Collaborations abroad are with the Pellegrini group at the Scuola Normale Superiore (Pisa, Italy) and with Prof. Ursula Wurstbauer at the Technical University of Munich (Garching, Germany). The projects explore frontiers of quantum physics and materials science. Junior scientists are being trained in very-low temperature techniques, semiconductor physics and advanced materials processing. Probing Spin in Topological Phases of Electrons Aron Pinczuk, Columbia University, DMR 0803691 Impact When embedded in high magnetic fields electron systems in artificial high quality semiconductor hetero-structures display intriguing phases that manifest the striking weirdness of quantum mechanics. Of primary interest are the intriguing even- and odd-denominator fractional quantum Hall effect states in the second Landau level. This project is a quest in which measurements of low-lying excitation modes, by advanced light scattering methods at very low temperatures, uncover exciting new electron physics that emanates from quantum interactions in reduced dimensionality semiconductors. Progress in understanding such fundamental physics and materials science advance the state-of- the-art in technologies of contemporary and future electronics and optoelectronics.